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Probiotic microorganisms have been shown to provide specific health benefits when consumed as food supplements or as food components. The main problem of such products is the poor survival of the probiotic bacteria in the low pH of gastric fluid. However the use of synthetic excipients for enteric coating to prevent the exposure of microorganisms to gastric fluid is limited in food supplementary industry. Therefore the aim of this study was to develop an enteric coating formulation containing shellac as a natural polymer. Shellac possesses good resistance to gastric juice; the major disadvantage of this polymer is its low solubility in the intestinal fluid [1, 2]. Thus films containing different ratios of shellac and water-soluble polymers (sodium alginate, hydroxypropyl methylcellulose (HPMC) and polyvinylpyrrolidon (PVP)) or plasticizers (glycerol and glyceryl triacetate (GTA)) were prepared in order to analyse the films’ melting temperatures (Tm), the changes in enthalpy (ΔH), their capability of taking up water, and their solubility in different media. The release characteristics of the films were studied by loading pellets with Enterococcus faecium M74 and coating them with formulations containing different amounts of shellac and polymer or plasticized shellac. Using dissolution tests, performed according to USP XXXI paddle method, the resistance of the coatings to simulated gastric fluid (SGF, pH 1.2) and the release of cells in simulated intestinal fluid (SIF, pH 6.8) was investigated.
The trials showed that an increasing amount of plasticizer results in a decrease of Tm and ΔH of the films whereat glycerol had a superior plasticization effect to GTA. The compatibility of films made of water-soluble polymers and shellac was also concentration dependent. HPMC and PVP showed superior compatibility with shellac compared to sodium alginate, since films containing shellac and more than 10% [w/w] sodium alginate tended to separate into two phases. In the end five formulations containing shellac and either 5% [w/w] glycerol, 10% [w/w] PVP, 20% [w/w] PVP, 10% [w/w] HPMC, or 5% [w/w] sodium alginate emerged as feasible for enteric coating purposes.
It was the purpose of this study to develop an oral oligonucleotide delivery system based on thiolated polymer/ reduced glutathione (GSH) system providing protective effect towards nucleases, permeation enhancement and controlled drug release. Polycarbophil-cysteine conjugate (PCP-Cys) was synthesized by the covalent attachment of cysteine to polycarbophil via amide bond formation. Incubation of 30-mer phosphorothioate oligonucleotide with DNase I and freshly collected intestinal fluid were performed in order to evaluate the protective effect of the polymer. Based on PCP-Cys conjugate together with GSH, permeation studies were performed on Caco-2 monolayer cell culture and on freshly excised intestinal rat mucosa in Ussing chambers. Additional drug release studies of tablets containing PCP–Cys, reduced GSH, and the oligonucleotide were performed in 100 mM phosphate buffer pH 6.8.
PCP-Cys displayed 223±13.8 μmol thiol groups per gram polymer. After 4 h the unprotected ODNs, which were incubated with DNase I and intestinal fluid, were significantly degraded by 61 % and 80 %, respectively. In contrast, less than 41 % (in DNase I) and 60 % (in intestinal fluid) of the ODNs were degraded in the presence of 0.02 % (m/v) of PCP-Cys. Permeation studies demonstrated due to the addition of PCP-Cys/GSH an 8-fold and 10-fold increase in the apparent permeability coefficient (Papp) on Caco-2 monolayer and on intestinal rat mucosa in comparison to the buffer only, respectively. Tablets containing PCP– Cys, GSH, and oligonucleotide showed a sustained drug release over 2 h. According to these results the PCP-Cys/GSH system might be a promising tool for the oral administration of oligonucleotide.
This work was supported by a scholarship from the Austrian Federal Ministry for Education, Science, and Culture to RM.
Mupirocin-loaded microparticles (MP) were designed to control drug release at the skin surface assuring that drug remains localized at the application site and does not unnecessarily enter into the systemic circulation . These reservoirs release active ingredient over an extended period of time maintaining effective drug concentration on the skin, at the same time reducing undesired side effects.
The goal of this research was to design controlled release MP with acrylic polymer using spray-drying technique and assess influence of feed composition (in terms of native drug/polymer physical form and solvent used) and preselected drug loadings (1:5 and 2:1 (w/w) drug:polymer proportion) on MP performance under the same processing conditions. Physicochemical properties of MP were evaluated using thermal (MDSC, TGA), spectroscopic (FT-IR) and X-ray analyses and correlated with encapsulation efficacy and in vitro drug release achieved. Morphology and particle size were determined using low angle laser light scattering (LALLS) and scanning electron microscopy (SEM).
Spray-drying of feed dispersion has formed partially coated crystalline MP with reduced encapsulation efficacy, irregular morphology and poor ability to control drug release irrespective of drug loading. Conversely, solid dispersions prepared from spray-drying feed solution have shown that drug/polymer miscibility, morphology and in vitro drug release were dependent on drug loading and solvent used . The superior control of drug release from MP was achieved for the higher drug loading (2:1 (w/w) drug:polymer proportion) using solvents in the following order: methanol ≈ methanol+ethanol(50:50) > isopropyl alcohol+acetone (40:60). MP were amorphous, with smooth and spherical morphology. The higher polymer loading (1:5 (w/w) drug:polymer proportion) yielded less control over drug release regardless of solvents used, with MP exhibiting significantly different morphologies.
Acrylic-based solid dispersions were confirmed as suitable microcarriers for controlled drug release using simple and scaleable spray-drying technique.
Monoglycerides, Phytantriol and a few other lipophilic molecules self-assemble in bulk in presence of water to form well defined liquid crystalline phases. Their structure can be tuned by temperature variation and/or by addition of oils. This leads to gel-like or fluid systems with a large internal interface between water and oil domains with different bulk viscosities. These nanostructured phases can be dispersed in the excess water phase by addition of an external stabilizer and energy input leading to internally self-assembled particles, so-called ISAsomes [1–4]. These ISAsomes are potential carrier systems for hydrophilic, amphiphilic and lipophilic functional molecules.
The hierarchical structure can be extended to a next level by gellifying the continuous aqueous phase by the addition of polymers like κ–Carrageenan or Methylcellulose. This leads to a new type of hydrogel, loaded with ISAsomes [5, 6]. Differently to the original oil-continuous bulk phase, the viscosity of this, now water-continuous, system can be varied in a wide range by composition. These gels can even be dried into foils and re-dispersed on demand.
Finally, we can use the oil-continuous nanostructured bulk phase to create concentrated, stable water in oil emulsions having a paste-like consistency and water content from 50% up to 90% by volume. No additional stabilizer is needed to create these systems. They have a great potential as delivery systems for functional molecules in very different fields like pharmaceutical and cosmetic applications, as well as in food science and agro-chemistry.
Lactose intolerance is the inability to metabolize lactose because of the absence of the enzyme lactase. It is estimated that 75–90% of birth lactase levels are lost by most people after weaning. The prevalence of lactase deficiency ranges widely with the ethnic background from 2–15% among Northern Europeans to 95–100% among Asians . Nowadays, lactose intolerance is usually controlled by strict adherence to a loactose-free or lactose-reduced diet. Moreover, as an alternative, capsules or tablets containing microbial-derived ß-galactosidase are available. However, this treatment is inconvenient for patients since these formulations have to be administered immediately before or together with lactose-containing diet because of their short-acting effect.
Therefore, the present work is aimed to develop an innovative long-acting peroral formulation for the treatment of lactose intolerance.
Biodegradable and biocompatibale polymeric microcarriers (2.78±1.05μm in diameter) were manufactured from poly(D,L-lactide-coglycolide) (PLGA) using spray-drying. They were functionalized with β-galactosidase from Kluyveromyces lactis and targeted with wheat germ agglutinin (WGA), which might prolong the residence time of particles in the small intestine. The particle-bound enzyme activity, the mucoadhesive as well as the cytoadhesive properties were assessed.
The highest particle-bound enzyme activity (1470 U ß-galactosidase per gram PLGA) was obtained with hexamethylene diamine as a spacer using carbodiimide method representing a 6-fold increase as compared to particles without spacer. Surface immobilisation of WGA enhanced considerably the particle binding to porcine mucin layer (mucoadhesion) and Caco-2 cell monolayers (cytoadhesion).
PLGA-microparticles, surface-modified with active ß-galactosidase as enzyme substitute and WGA as a targeter, are able to bind to enterocytes and thereby to prolong the intestinal residence time. It is a promising approach towards a promising approach towards a more convenient therapy of lactose deficiency and intolerance.
Skin is main target for UV-oxidative stress and their antioxidant defenses can be quickly overcome. The consequences are reflected at the molecular and cellular level. Here, most important organelle included in survival pathway are mitochondria. Recently significant activation of mitochondria-mediated signaling cascades by resveratrol (RSV) has been discovered .
RSV is a naturally occurring polyphenolic phytoalexin, which has many beneficial biological effects but on the other hand possess some limitations. Few of these are: poor water solubility, high metabolic rate and frequent dosage–dependent effect in the cellular environment . One of recent progresses that can satisfy all these obstacles of RSV is design of nanosized drug delivery system .
The protective effects of RSV in solution or loaded into SLN (SLN-RSV) on radiated keratinocytes were studied comparing with the effects on non-radiated cells.
Cosequences of damaged effect of UV-radiation was slightly changed cell morphology, as some fragments of actin fibers appeared and mitochondria activity was weakened and they were dispersed over whole cytoplasm. However, only SLN with incorporated RSV at 100 μM preserved normal cell morphology and improved mitochondria activity, while the other samples (RSV at 10 or 100 μM and also SLN-RSV at 10 μM) showed any significant difference regarding radiated control cells. These effects are ascribed to the transfer of RSV by nanoparticles intracellularly – integrating among mitochondria, where RSV can best realize its “anti-stress” potential.
To conclude, the results clearly revealed the hypothesis that loading of RSV into SLN significantly improve bioavailability and diminish UV-related damage of keratinocytes, and thus providing better photoprotection of cells compared to the application of RSV in solution.
Cationic SLN formulations were developed and optimized in terms of cationic lipid/surfactant ratio and production parameters. 5wt% of Compritol 888 ATO (COM, Gattefosse) or Imwitor 900(IMW,BASF) were used, 0.4–1.0wt% of cetyltrimethylammonium bromide (CTAB, Sigma) and 0.1–1.0 wt% of Lutrol F68 (BASF) were tested. Formulations were produced in triplicate. SLN were prepared by modified microemulsion method , which was further optimized in terms of velocity and time of high shear homogenization step. Freeze-drying was performed on DuraDry MP at −45°C/184 mT during 6 days. Samples were freeze-dryed with 5.0% or 10.0% of Glucose (Sigma) or Sucrose (BDH Chemicals) or without cryoprotectants. Reconsitution was performed by rehydratation, vortexing during 3min and applying ultrasound during 30s. A Zetasizer NanoSeries (Malvern) was used to determine average hydrodynamic diameter (z-ave), polydispersity (PdI) and zeta potential (ZP)
Optimized formulation consisted of 5.0% solid lipid, 0.5% CTAB and 0.25% Lutrol F68, yielding particles with z-ave=159nm, PdI=0.34 and ZP=54.8 mV (IMW) and z-ave=180nm, PdI=0.272 and ZP=56.2 mV (COM). These parameters remained unchanged during 8 days of storage at 8°C. Samples dried without cryoprotectants yielded light powdery product which could be redispersed easily; freeze-dried samples with saccharides tested yielded solid products.
Cationic SLN formulations intended for gene delivery were designed and optimized. Particles with z-ave below 200nm and low PdI were produced. These SLN showed good stability of 15 days .Suitability of cationic SLN for freeze-drying without cryoprotectants was confirmed .
The authors whish to thank Dr. Fernando Nunes for cooperation in freeze-drying experiments. This work was supported by grant SFRH/BD/60552/2009 from FCT and by Nadacia Slovenskeho Plynarenskeho Priemyslu.
Pharmaceutical secondary manufacturing has long stood in stark contrast to the drug discovery end of the business, as well as to other sectors, when it comes to innovation such as continuous manufacturing. Is that about to change? The traditional business model is breaking down with consequent pressures on all parts of the pharma value chain. Manufacturing’s contribution to improving yield, reducing time, cost and waste is increasingly critical. Regulation which previously had insisted on batch testing is now moving to be much more supportive of real time product release and process analysis, heralding a future where the validation and establishment of continuous manufacturing will be easier.
Integration of each process stage is crucial for continuous manufacturing. However, pharma companies tend to work with ‘islands of automation’ where every unit of operation is more or less an independent from an integration point of view.
Another key barrier is that these changes require companies to work in a more multi-disciplinary way, crossing system worlds. For the first time, if you are in analytics you have to speak to people in process control and so on. Multi-disciplinary teams are an absolute must but not everyone is ready for that. The relatively slow uptake of process analytical technology (PAT), crucial for continuous manufacturing, following the FDA’s 2004 PAT initiative, highlights the challenge facing companies.
Mindset changes and internal culture changes will be key to the successful introduction of PAT as a first step towards continuous manufacturing. The companies that are first to overcome the barriers will not just reap the reward of increased competitiveness. Because of the stage of its introduction, they have the opportunity to implement the technology to a higher level than in industries where it is already established. From being a laggard, secondary manufacturing has the potential to become a trendsetter.
Granular flows are of paramount importance in industry and nature. To understand, e.g., the effect of various process parameters on the final product performance is critical. In industry, the flow in agitated mixing equipment basically consists of granular flow over a blade. While previous experimental and numerical work [1, 2] could reveal some features of this flow situation, information like single-blade mixing efficiency or the principal parameters that influence this flow are still scarce.
We performed excessive high-speed video imaging of dry and wet granular flow under a controlled atmosphere in a 3D mixer as well as in a novel 2D flow setup. We use particle image velocimetry (PIV) to measure the velocity of the granular bed from the top (3D system) as well as in a cross section of the blade. Discrete-Element-Method (DEM) simulations are used to help interpreting our experimental results. The ultimate goal was to quantify the mixing in bladed mixers (e. g., high-shear granulators).
We show results for the instantaneous, time-averaged as well as fluctuating velocity fields for the flow over a single blade. Our results indicate that the bed height in front of the blade has a significant effect on the flow pattern. Also, the flow situation changes when multiple blades are used and the blade-to-blade distance is changed. Finally, we quantify the mixing efficiency of a single-blade passage using image analysis.
Porous particles are present in various technical applications as well as in the field of medical treatment. The latter involves amongst others the production of highly porous and respirable particles to serve as solid inhalants and substitute intestinal medication. One promising way of manufacturing such biotechnological therapeutic agents is the lyophilisation of single drops or sprays – a complex technological approach that still requires research and process layout. Besides experiments, numerical flow simulations are capable of providing insight into the physics that influence the transport and mass and heat transfer related to porous particles. Predicting the corresponding multiphase flows requires knowledge of the behaviour of porous particles in comparison to solid ones. By performing fully-resolved direct numerical simulations (DNS) of single complex particles correlations between particle properties and their fluid dynamic behaviour are to be established.
In this work, the Lattice-Boltzmann method (LBM) is used to simulate the flow around virtual lyophilisates and to calculate drag, lift and torque coefficients . A future aim is to perform simulations of the sublimation process of frozen spray droplets which are numerically realized in form of heterogeneous particles. In a first approach, the highly-porous lyophilisates are modelled by creation of simplified aggregates consisting of spherical primary particles (Fig. 1, left). This base structure is covered by a mutable hull-shaped matrix to represent the second phase of the frozen solution of the medical agent which is shrinking due to sublimation (Fig. 1).
This work was supported by Deutsche Forschungsgemeinschaft (DFG grant SO 204/36-1, SPP 1423).
Numerical methods such as Finite Element Analysis (FEA) or Computational Fluid Dynamics (CFD) are considered to be well established technologies in industrial design and engineering. While the methodology of numerical simulation is fully recognized in conventional industry (e.g. automotive, aviation, construction, machinery) even (especially) for critical application, pharma-industry and biotechnology have just started to carefully consider numerical simulation methods as valueable tool to create a sound understanding of their processes. The high level of regulation in this specific industry as well as the strong drive for evidence based validation (verfication) may have contributed to the fact that numerical simulation methods are hardly applied in pharma industry and biotech.
The paper in hand shall demonstrate on typical applications how the CFD approach can be applied to design and optimize processes, to create additional knowledge about specific process interactions, to provide better understanding about correlations between process parameters and product quality, to supply a sound data base for process validation and thus to increase process flexibility. In four different references various aspects of the CFD methodology are discussed. The operational performance of a fermenter is presented with specific focus on gas distribution (oxygen) depending on mixer and vessel design and on shear stress exposure of the cell culture. Also, a stirred and heated storage vessel for thermal sensitive emulsions is investigated. Especially the temperature distribution within the products related to the temperature of the heating jacket and stirrer parameters shall be analysed. A third application considers a very specific freeze technology for protein-buffer-solutions. The freeze and thaw process is analysed by CFD under specific consideration of temperature induced concentration shifts in the protein-buffer. Finally a standard vessel-agitator set-up is discussed and strategies for process optimizations are presented based on CFD. Based on this specific problem it shall be demonstrated how CFD can support process-upscaling from lab to industrial size.
This contribution describes the dynamic optimization of a pharmaceuticals batch dryer. The optimal control problem is based on the control vector discretization or single shooting method, thus a non-linear programming (NLP) problem is obtained. The target of the open loop optimization problem is the batch time minimization and the control variables are the On/Off intervals of the mixer and the mixer rotation speed. In order to implement a relevant scenario from practical point of view the following constraints are applied: the on and off intervals have same duration, the stirrer speed is constant during the entire batch drying process and the final moisture specification must be met. Finally, an upper limit on the fines fraction in the particle size distribution is set. The dryer model  consists of a system of partial differential equations coupled to a population balance model which describes the breakage process. The optimization problem presents several local minima and low gradient regions, thus a gradient based method fails to converge to the minimum. Therefore, a genetic algorithm-pattern search (simplex) method is used to ensure convergence of the optimization problem. The relevance of the work is highlighted by recent contributions which deal with the operation optimization of this unit operation [2–5].
In the pharmaceutical industry spray coating is a frequently used method to apply a film layer on the surface of tablets or pellets. The function of coating ranges from the controlled release of active pharmaceutical ingredients (APIs) to taste masking and coloring. A widely used technique is drum coating, where tablets are placed in a rotating drum and the coating liquid is sprayed onto the moving tablet bed surface. One of the most central quality attributes is the uniformity of coating, both inter-tablet and intra-tablet. Besides experimental work , numerical simulations have become an extremely important tool in process design and development.
Coater performance depends on a range of different parameters, which could be essential for the quality of the final product. In order to quantify the impact of different CPPs (critical process parameters) on the related CQAs (critical quality attributes), the combination of advanced numerical methods on different scales is necessary. In this work we present an innovative approach to analyze, understand and optimize important steps of the pharmaceutical tablet coating process by means of numerical simulations. The final outcome is the application of the developed methods to industry-scale processes.
Concerning our numerical multi-scale approach, the Discrete Element Method (DEM) is used for the simulation of the tablet bed mixing. Furthermore, a detailed numerical analysis of the interaction between spray droplets and tablet surface is performed with multiphase Computational Fluid Dynamics (CFD) methods . On a larger scale, the CFD approach is also adapted to investigate the coater internal flow in terms of drying air and liquid spray efficiency.
Summarizing, the presented combination of simulation methods helps to gain a deeper understanding of the spray coating process, providing a further step away from trial-and-error towards Quality-by-Design approach.
The impact of liquid drops on wetted and dry surfaces is a complex two-phase flow phenomenon with high technical relevance especially in surface coating. It is also of increasing interest in the development of novel drug dosage forms in pharmaceutical engineering. The complex physics after the impact, which is still not understood in full detail, has been investigated in numerous experimental and analytical studies. Based on dimensional analysis and/or simplifying assumptions various semi-empirical correlations and analytical solutions have been derived to describe the individual stages of the motion of the liquid (see, e. g. [1, 2]). The present work numerically investigates the whole process of the liquid spreading after the impact using the CFD software FLUENT. Impact velocities and surface wettabilities were varied in the considered cases. It is shown that the Volume of Fluid based approach, which has become a standard numerical method for two-phase flow simulations, generally captures the typical flow features, like splashing (see Fig. 1), qualitatively and quantitatively very well. As such the computational results agree very well with the experimental data and analytical asymptotic solutions obtained for the individual regimes in literature. Notable discrepancies were however observed at the late stages of the liquid spreading on dry surfaces, where the outer rim of the liquid lamella eventually starts to recede. This deficiency points at the great numerical challenge to capture accurately the dynamics at the contact line between the liquid, gas, and the solid surface. The strong sensitivity of the incipience of liquid receding to the contact physics becomes very evident here.
Magnetoliposomes (MLs) are phospholipid vesicles encapsulating magnetic nanoparticles utilised as contrast agents for targeted molecular Magnetic Resonance Imaging (MRI). There are different methods of preparation and characterization of liposomes containing ultra small paramagnetic iron oxide ions (USPIOs) i. e. lipid film hydration method  or reverse phase evaporation . In this work as magnetic core we have used commercially available dextran coated iron particles (Molday-ION, purchased by Bio-Pal, USA), with a colloidal size of 30 nm. Liposomes were prepared by thin lipid film hydration method: a predetermined mixture of lipids made of phosphatidylcholine, with or without cholesterol and small amounts of PEG-ylated lipids (which sterically stabilize the liposome reducing their usual rapid uptake from the immune system) was dissolved in organic solvent and evaporated to dryness. Then the dry lipid film was hydrated with a buffered aqueous solution of different concentration of dextran magnetite. The resulting MLs, which were heterogeneous in their size, were centrifuged suddenly after the hydration step to remove excess dextran magnetite; some MLs were sonicated before centrifugation with an Ultra Sonicator (50 min, 130 Watt) to obtain a homogeneous particle size. Physical characterization was performed by dynamic light scattering (DLS) to determine the mean particles diameter and the size distribution. These data were compared to morphological images obtained by transmission electron microscopy (TEM). Chemically, the absolute amount of Fe in MLs was determined by a colometric test using potassium thiocyanate (KSCN) as reagent. MRI measurements were performed in vitro in agarose gel phantoms to evaluate the intensity of the contrast agent on T1 and T2 relaxation time. In vivo, the biodistribution and the cleareance of the particles over time were studied in mice. MLs have shown a high negative and positive enhancement in MRI and due to this strong contrast effect they will be modified for non invasive diagnosis of atherosclerotic plaques by targeted molecular imaging.
Ultrasound active liposomes currently have gained a lot of interest as therapeutic agents for targeted drug delivery. A well known problem is their fast clearance from the circulation and thus the short time frame for drug release. The use of ultrasound as external trigger for drug release is attractive because it can be easily focused and only few adverse effects on the healthy tissue can be observed.
To prolong the blood circulation kinetics the liposome surface can be modified with poly(ethylene glycol) (PEG) derivatives to prepare so called ‘Stealth’ liposomes. Lin and Thomas described that the PEG content in the liposome membrane influences the drug release during ultrasound application .
A new ultrasound contrast agent composed of dipalmitoylphosphatidylcholine or distearoylphosphatidylcholine and varying concentrations of polyethyleneglycol-40stearate was prepared using the thin-film hydration method. It was demonstrated that concentrations of 1 mol% and 10mol% polyethyleneglycol-40stearate show very good ultrasound activity. This result was unexpected due to the small size of only 100–200nm.
The aim of this study was to determine the physico-chemical properties and the structural behavior of these contrast agents. Therefore 31P-NMR measurements, AFM investigations and TEM images were correlated. A combination of these methods should enable us to distinguish between organisations such as micelles, SLN and liposomes.
The authors would like to thank the DFG “Forschergruppe Nanohale 695” for support.
Specially engineered drug particles can solve solubility and formulation problems, which are major challenges for the pharmaceutical industry. Particle size reduction of poorly water soluble drugs results in increased dissolution rate and higher bioavailability or better processability as demonstrated in previous studies [1, 2]. High-pressure homogenization can be used to decrease particle size, since it induces cavitation forces and causes highly localized increase in temperature and pressure within the fluid, resulting in decrease of particle size and inhibition of agglomeration. The current study is focused on properties inherent to particle engineering as well as methods for production and characterization of micro- and nanocrystals. The meloxicam, a low molecular weight analgetic for oral administration, exhibits a slow dissolution, therefore, it was formulated as micro- or nanosized particles by high-pressure homogenization. The samples were freeze-dried and characterized regarding particle size, morphology, structural analyses (DSC, XRPD) and in vitro dissolution rate. The final formulations were free of organic solvent and contained micro- (4–8 μm) or nano-sized (400–1000 nm) meloxicam crystals. Meloxicam in vitro dissolution rate was significantly improved and its particle size was found to be dependant on stabilizers used. To conclude, the new meloxicam formulations can potentially expand its application also to alternative administration routes (e. g. pulmonary and intranasal).
This work was supported by TÁMOP-Hungary research project: Development of teranostics in cardiovascular, metabolics, and inflammatory diseases (TÁMOP-4.2.2-08/1-2008-0013).
The availability and use of appropriate Process Analytical Technology (PAT) is fundamental to achieving the transformed style of pharmaceutical manufacture that is envisaged by the regulators. Implementing the knowledge-driven, risk-based approach to development and manufacture described in ICH Q8, Q9 and Q10 Guides, and adopting more efficient, modern operating practices, depends on being able to reliably identify, analyze and control those parameters that dictate pharmaceutical performance. This paper examines the potential contribution of laser diffraction particle sizing technology within this context, focusing on the use of industrially proven on-line solutions for real-time measurement and automated process control.
Particle size has a controlling effect on the behaviour of many pharmaceutical products, often influencing critical to quality parameters such as dissolution rate, bioavailability and product stability. Where this is the case, the robust and proven technique of particle sizing by laser diffraction has for many become the method of choice. Non-destructive, with measurement rates sufficiently rapid for real-time monitoring, laser diffraction transitions easily, from the laboratory through to on-line measurement within the pilot plant, or in a manufacturing environment. With on-line analysis in place, the design, optimization and control of unit operations such as granulation, spray drying and, perhaps most importantly, milling becomes simpler and much more effective. Case studies illustrate this, the most compelling describing the use of on-line laser diffraction technology to fully automate control of a mill such that the particle size of the exiting active is maintained within specification despite variations in feed quality.
The aim of Process Analytical Technology (PAT) is to gain deeper insight in pharmaceutical manufacturing processes, replacing empirical approaches by knowledge-based procedures. A detailed understanding of the key parameters of a process and their impact on the product quality allows companies to “build in quality” instead of “testing it into the final product”. From this point of view, PAT has to be tailored for a direct implementation to manufacturing lines to measure in real-time the key parameters of the process.
Here, we present results on real-time quantitative in-line monitoring of powder mixing processes by near-infrared (NIR) spectroscopy [1, 2]. Spectral data collection and data analysis was performed in real-time based on partial least squares models developed via dynamic calibration. Different strategies are followed: I) Application of a single reflection probe to determine the mixing endpoint. II) A novel multiple reflectance probe measurement system for a spatially resolved monitoring of the powder flow kinetics within a blender. The parameters from the mixing process are linked to keyparameters of powders, obtained from rheometric investigations based on experimental design.
Beside the batch processes monitored here with NIR spectroscopy, we also introduce hyper spectral imaging for monitoring fast continuous processes and non-invasive product quality analysis of solid dosage forms.
Near-infrared spectroscopy (NIRS) is a rapid and nondestructive analytical method. The use of near-infrared spectroscopy in the pharmaceutical industry has been rapidly increasing over the past decade, with particular interest in the analysis of solid dosage forms, such as tablets and capsules . This article describes use of NIR spectroscopy to determine of content the active pharmaceutical ingredient (metformin hydrochloride) in tablets, as well as strength tablets. Our goal is to create a necessary basis of spectral data and develop an optimal chemometric models that will later be transferred and used for monitoring the process. The calibration set was made up of 100 laboratory and 180 production samples in which the content of the active ingredient varied from 90 % to 110% of the declared value. The set of calibration samples, used for determination of the tablet hardness, included 70 laboratory and 70 production samples, which were compressed using four levels of compression force. The API content is determined by the validated HPLC method, while Erweka hardness tester was used to determine tablet hardness. NIR spectra analysis by using method of partial least squares . The best result for drug content determination was obtained for the raw spectrum, where the coefficient of correlation for calibration model was 0.99945, RMSEC 0.552, and RMSEP 0.570, with seven factors used. The model which gave the best results for the tablet hardness determination was obtained by second-derivative spectra (coefficient of correlation: 0.99616, RMSEC: 0.506 and RMSEP: 0.841).
According to the obtained results, it was concluded that both models ensured a high coefficient of correlation as well as low level of error of the calibration model and prediction. It can be concluded that NIR spectroscopy, a rapid and nondestructive technique, is a powerful tool that can be easily implemented, with appropriate technical solutions, in the production process, thus ensuring its on-line or in-line monitoring.
The use of nano-sized materials (NMs) offers exciting new options in technical and medical applications. Adverse effects on cells and organs, however, have also been reported. It is known that NMs may interfere with conventional assays. It may be suspected that inter-cell line differences in the sensitivity to NMs also exist. NMs may also interact physicochemically with plasma membranes. Cells in suspension, where a relatively large area is exposed, may therefore react different from adherent cells. As NMs by interaction with the replicative machinery may inhibit proliferation, also the proliferation rate (length of the doubling time) may be an important parameter.
To assess the effect of the medium 20–1000 nm large carboxyl polystyrene particles (CPS) were tested in the presence of different amounts of fetal bovine serum. Potential interference was evaluated by testing in the cytotoxicity screening assays WST-1, MTT, MTS, Neutral Red, Sulforhodamin B, leucine incorporation and ATP content. IC50 concentrations were compared between 20 different cell lines.
The size of small (20–60 nm) CPS increased markedly from medium with 0% to 10% FBS; for larger CPS only minimal differences were seen. 20 nm CPS in medium with 0% FBS acted cytotoxic in all cell lines. 20 nm CPS in 5% and 10% FBS and larger CPS in all media were only minimally cytotoxic to nonphagocytic cells. In phagocytic cells also CPS of ≥ 500 nm acted cytotoxic. Half maximal inhibition concentrations (IC50) in a given cell line did not differ markedly between the screening assays but varied more than 10 times between the cell lines. IC50 values were significantly lower in suspension cells. Large cells and human cell lines with long doubling times were more resistant to the cytotoxic action of 20 nm CPS.
In addition to medium composition, growth characteristics, proliferation and cell size of the cell line used for testing may influence the IC50 values of NMs. Cells in suspension are especially sensitive to the cytotoxic action of small carboxyl polystyrene nanoparticles.
This work was supported by the FP6 European integrated project “NanoBioPharmaceutics”, NMP4-CT-2006-026723 and by the RPC project ‘Nano-structured Materials for Drug Targeting, Release and Imaging’.
Praziquantel (PZQ) is a drug active against all species of Schistosoma and it is the drug of choice for the treatment of schistosomiasis . Due to its low water solubility and risk of parasite resistance or tolerance to PZQ, it would be useful to develop a novel pharmaceutical product that could increase its therapeutic efficacy and improve the bioavailability. Solid lipid nanoparticles (SLN) combine the advantages of different colloidal carriers and also avoid some of their disadvantages in relation to the stability and possibility of large scale production. Thus, the aim of this work was to develop SLN containing PZQ (SLN-PZQ) and evaluate the cytotoxicity in the HepG2 cell line. The SLN were produced by a modified of the oil-in-water microemulsion method  using stearic acid as lipid core and poloxamer 188 as surfactant. The PZQ was incorporated in lipid core for the production of SLN-PZQ. Particle size was measured by dymamic light scattering (DLS) and the electrophoretic mobility was measured by laser Doppler anemometry. The cytotoxicity of PZQ (dissolved in ethanol) and SLN-PZQ was examinated in the HepG2 cell line using AlamarBlue assay . The prepared SLN-PZQ had a mean particle size of 480.4nm with a zeta potential of −36.5mV. In HepG2 cell cultures, the tested SLN-PZQ suggested a decreased toxicity of the drug when delivered by SLN, in comparison to a conventional PZQ solution of similar concentration. The degree of toxicity was shown to be dose-dependent.
This work was supported by CAPES.
Many current dermatological preparations, sunscreens and other cosmetics, contain nanosized particles (NPs), which were observed to be rapidly internalized by keratinocytes . Besides their ability to enter into cells, NPs can be responsible for higher toxicity compared to bigger particles, mainly due to their larger surface area and enhanced chemical reactivity. Application of NPs increase the risk of cell damage and consequently cause alterations in mitochondria, actin filaments, cell membranes, etc., usually resulting in diminished cell functions or even cell death . Despite the fact that ZnO and/or TiO2 NPs are frequently used, only few long-term toxicological studies are available. Our research was focused on long-term investigations, where the effects of repeated application of ZnO and TiO2 NPs on keratinocytes were evaluated. The preliminary short-term experiments showed no adverse effects of ZnO and TiO2 NPs on viability and morphology of keratinocytes in concentrations up to 15 μg/ml. Furthermore, TiO2 NPs did not significantly affect cell viability as well as cell growth in concentrations up to 100 μg/ml. Oppositely, ZnO NPs decreased cell viability in concentrations above 20 μg/ml sharply, and caused detachment of keratinocytes. Thus, the keratinocytes can survive short-term exposure to low concentrations of ZnO and TiO2 NPs, however, question regarding cell ability to maintain essential functions during their life span arises. Therefore, the concentration that did not show any cytotoxicity in short-term experiments was used for long-term investigations.The results after 3 months continuous treatment with 10 μg/ml NPs showed no significant changes in generation of reactive oxygen species (ROS) compared to untreated cells. Microscopical observation of cells continuously exposed to TiO2 indicated unchanged cell surface and presence of endosomes filled with TiO2 NPs, which were enlarged compared to endosomes of untreated control cells. Contrary, exposure to ZnO caused significant decrease in cell number as well as appearance of dense nuclei and disappearance of visible actin filaments, elevated ROS levels and decreased mitochondrial activity, indicating oxidative stress as a main cause for cytotoxicity of ZnO NPs. To sum up, the results indicate that the right selection of NPs is crucial for formulation of safe dermal products.
The oral cavity acts as a complex barrier and displays the first main hindrance against uncontrolled uptake of a variety of substances. The oral mucosa represents 60% of the total surface area within the oral cavity, offers a good opportunity for drugs to be absorbed and shows a 4 to 4.000 times greater permeability than the skin.The barrier function of this tissue is mainly guaranteed by i) the saliva, ii) the mucus layer, iii) the cell junctions in the epithelium and iv) the membrane coating granules. However, as the permeability of drugs through the oral mucosa is limited, new delivery carriers have to be developed. Nanostructured materials (NMs) are small enough to overcome this tissue. Within the development of such nano-carriers, the efficacy as well as the safety are important factors that cannot be neglected. Currently, no standardized physiological in vitro models, evaluating the permeability, transport route and toxic effects of NMs are available.
NMs (polystyrene particles (PS), silver particles Ag)) were primarily characterized in terms of size and surface charge in physiological media. The penetration of the particles was investigated through excised buccal mucosa from pig. The in vitro permeability studies were carried out with Franz diffusion cells. It is a fact that the diffusion barriers in the buccal mucosa are only functional within living cell layers. Therefore, the viability (MTT) and the structural integrity of the membrane (methylene blue/PBS with and without EDTA) were investigated. The transport studies were carried out with Transwells® and the Trans-Epithelial Electric Resistance (TEER) was measured. The particle uptake into the cells was recorded with fluorescence/electron microscopy and the cell damage was evaluated. Results: The results demonstrate that the permeability of the particles depends on the size, surface charge, hydrophobicity and particle concentration. Particles in sizes of 20 nm (PS) and 35 nm (Ag) permeated the mucus layer and penetrated in the stratum superficiale of the top third region of the epithelium. They did not affect the tight junctions and were taken up by the cells. The cellular uptake correlated with the cell damage. Particles in sizes of 150 nm (Ag) and 200 nm (PS) aggregated in the saliva, were entrapped in the mucus layer and could not enter the top third region of the epithelium. Additionally, they also did not affect the tight junctions and no cellular uptake could be recorded.
Independent from the material small (20–35 nm) NMs showed a much higher penetration than larger (150–200 nm) NMs.
Studies on nasal epithelial models are important to develop vehicles for systemic nasal drug delivery, and also for targeting drugs to brain via the nasal route. RPMI 2650 human nasal septum carcinoma cell line was used in our experiments as an in vitro cell culture model for toxicity and permeability assays.
For toxicity tests cells were cultured in 96-well plates, and MTT dye conversion and lactate dehydrogenase release were determined after treatments. For permeability tests RPMI 2650 cells were cultured on collagen-coated Millipore CM inserts (hydrophilic PTFE membranes, pore size: 0.4 μm, surface 4.2 cm2) in 6-well plates. Fluorescein was selected as a marker of paracellular permeability, and TEER and Papp were measured.
RPMI 2650 cells passaged at high cell density grew as confluent multilayers on inserts. To induce barrier properties several treatments and culture conditions were tested. The effects of serum, hydrocortisone, cAMP and air-liquid interface on RPMI 2650 cell layers were examined. Hydrocortisone and cAMP increased the tightness of the nasal epithelial barrier, and induced the expression and junctional localization of claudin-1, claudin-4, ZO-1, and β-cathenin visualized by immunohistochemistry and confocal microscopy. The changes in cell and junctional morphology were confirmed by electron microscopy. The resistance of the monolayers reached 240 ± 13 Ωcm2, and Papp of 2.7 ± 0.2 10−6 for fluorescein indicating a barrier typical for nasal epithelium. The model was used to test the non-toxic nasal doses of absorption enhancers Tween 80, Cremophor RH40, Transcutol P, and water soluble sucrose esters and to determine their effects on paracellular permeability. Tween 80 and Cremophor RH40 decreased TEER by 50 % and significantly increased Papp values of RPMI 2650 layers.
We have successfully established a human in vitro nasal epithelial model that can be used to study the effects of absorption enhancers and their mode of action.
This work was supported by TÁMOP-Hungary research project: Development of teranostics in cardiovascular, metabolic, and inflammatory diseases (TÁMOP-4.2.2-08/1-2008-0013).
Nanotechnologies and Nanomedicine are promising fields of scientific research. Experts expect a huge economic and social impact from Nanotechnologies and Nanomedicine in the next decades. New properties associated with size smaller than 100 nm opens a new world of applications. At the same time, possible toxicological aspects associated with nanotechnologies are being discussed in the scientific community. Nanotoxicity, possibly resulting from altered chemical and physical behaviour of nanoparticles compared to bulk material, is a major concern nowadays. These phenomena are believed to be related to the extreme high specific surface area and altered electrochemical properties of nanoparticles. The investigation of nanomaterials in terms of their toxicological behaviour is an extremely multidisciplinary challenge. Toxicology of non-nano chemicals is a well established procedure. Unfortunately, Nanotoxicology is quite more complicated and standard protocols in Toxicology can not be used. Nanomaterials have to be investigated in detail for different parameters like size, size distribution, shape, charge, etc. Furthermore, interaction with different matrices like blood, interstitial fluid, buffers, etc. influences significantly nanomaterials like, agglomeration, size distribution, charge, etc. In consequence, nanotoxicology needs new standardised protocols which are able to deal with the extreme complexity of nanomaterials and their toxicological behaviour!
To build a national contact point for nanotoxicology, the BioNanoNet as a network company, has initiated the build up of the European Center of Nanotoxicology (www.euro-nanotox.at). This virtual center unites all Austrian Experts in the field of Nanotoxicology and helps to develop standardized methods. EURO-NanoTox initiates research projects together with its members and is links Austrian activities in the field of nanotoxicology to European activities. Within this contribution the European Center for Nanotoxicology will be presented. The general strategy of a stepwise approach to investigate nanomaterials in respect of their potential toxic properties will be shown. Furthermore, some details for the investigation of skin penetration of quantum dots will be addressed.
Powder mixing is crucial for many processing stages within the pharmaceutical, catalysis, food, cement, and mineral industries, to name a few. A significant problem hindering process design is the paucity of information about the effects of changing process parameters on mixing efficiency, especially in the case of continuous mixing.
The main target of this talk is to highlight continuous mixing and to examin the effects of different process and design parameters. Interestingly, continuous processing has been utilized extensively by petrochemical, food, and chemical manufacturing but has yet to reach the pharmaceutical industry to a meaningful extent. Recent research efforts indicate that a well-controlled continuous mixing process illustrates the capability of scale-up and ability to integrate on-line control ultimately enhancing productivity.
In this talk we will decribe the use of engineering methodologies to design continuous pharmaceutical manufacturing systems for solid dose products. We will examine the performance of gravimetric feeders and continuous mixers, and their integrated dynamics, and develop guidelies for the optimal design and operation of the integrated system. Variance components will be characterized, and the monitoring of performance using PAT tools will be discussed.
Xanthan (XAN) is a well known negatively charged biopolymer that adopts different conformations in media, which are still poorly understood. XAN tablets in contact with water hydrate, forming a gel layer that regulates the drug release rate . The hypothesis was that XAN molecular structure influences the drug release from matrix tablets. Thus, detailed studies on molecular as well as on macro-scale level were performed.
To determine XAN molecular conformations, its solution in water at pH 7.0 or 1.2 was deposited on freshly cleaved mica, dried and images were taken in air using tapping mode AFM. In order to determine Young’s modulus and investigate properties of single XAN molecule, nanoindentation as well as nanofishing were performed. Ingress of media into XAN tablet, gel structures and drug release were studied by NMR and MRI, oscillatory rheometer and dissolution USP Apparatus II.
Our results reveal that XAN adopts single chain conformation in water at pH 7.0, whereas at 1.2 double stranded structures are formed. This was confirmed by AFM images as well as by calculated parameters: persistence length of XAN in water was 210.37 compared to 116.83 in pH 1.2. Young modulus of XAN film in water was lower (1.52 GPa) compared to pH 1.2 (1.94 GPa). Higher rigidity of XAN films at pH 1.2 was further confirmed by formation of XAN gels, where elastic G’ and loss G” moduli were higher in the whole deformation range. Double stranded molecules form more cohesive gels, while single stranded are more flexible, due to the higher hydration of negatively charged polymer. MRI results proved much higher hydration and consequently the swelling of XAN tablets at pH 7.0 than at 1.2 and the thicker gel layer as well. Surprisingly, drug release in pH 1.2 media was faster regardless to firmer gel structure.
High rigidity and low hydration of XAN matrix in pH 1.2 are the consequence of XAN molecular structure regulating drug diffusion in tablets.
Dry powder coating is a relatively new technique to coat substrates without the use of any organic solvent or water. The film forming polymer is applied as a powder to the cores to be coated leading to reduced process times . Additionally, excipients like plasticizers, preferably in liquid form, are often needed to soften the polymer in order to get a functional film. A curing step is sometimes necessary to achieve film formation depending on the characteristics of the polymer used. One critical parameter in dry powder coating is the coating efficiency which describes how much of the applied coating material actually adheres to the cores. Therefore, another main task of the excipients used is to enhance the adhesion of polymer powder. The aim of this work was to evaluate excipients, like plasticizers and polymers, regarding their suitability for dry powder coating.
Dry powder coating was performed in a rotary fluid bed (GPCG1.1, Glatt, Binzen, Germany). Polymer powder and liquid were fed simultaneously via a three-way nozzle to the fluid bed. Coating efficiency was calculated by dividing the mass of adherent coating material by the mass of applied coating material. Theophylline pellets were used as cores and ethylcellulose, hydroxypropylmethylcellulose acetate succinate (HPMCAS) or Eudragit RS® as coating polymer. Various liquids were characterized with respect to several properties, like viscosity, spreading behavior and droplet size. Coated pellets were investigated via dissolution testing and scanning electron microscopy before and after curing steps to evaluate whether film formation was achieved.
The spreading behavior of the liquids seems to be one key factor affecting the coating efficiency. It can be investigated by measuring contact angles of liquids on the polymer or predicted by calculating surface energies. However, there are still other parameters impacting the coating efficiency of the process like viscosity of the liquid, which influences on the one hand the kinetic of spreading as well as the droplet size generated by the spraying nozzle. The film forming properties of the polymers used were very different. Using ethylcellulose a curing step was required to obtain dense films whereas Eudragit RS® formed films without any curing.
Coated pellets offer several advantages related to safety and effectiveness of the medicinal product such as reproducibility of gastric emptying and of absorption, and predictable plasma levels with lower probability of dose dumping due to modified release [1,2]. Layered pelletizing involves a process in which drug in solution, dispersion or powdered form is loaded onto inert starting cores. Starter inert cores have several benefits, such as they serve as nuclei with standardized shape, therefore the product shows more exactly defined surface for functional coating .
The objective of this study was to investigate the effects of formulation and manufacturing parameters on the pellet quality after the layering and coating process applying 3 types of inert core materials (sugar, microcrystalline cellulose, and isomalt). An additional objective was to investigate and compare the effect of the core material on the in vitro drug release of water soluble and poorly water-soluble drugs when they were coated with a permeable polymer membrane.
The drug layering and coating process were followed by non-destructive tests such as image analysis and NIR spectroscopy. Flowability, hardness, friability, wettability and morphology of starting cores as well as of finished products were investigated.
According to the non-destructive analysis and physical tests, all pellets manufactured from different core materials demonstrated satisfactory quality attributes. Since the type of inert core material may significantly influence the dissolution profile, the solubility characteristics of both the drug and core material should be considered.
Hot Melt Extrusion, proven state-of-the-art technology in the field of plastics, is becoming increasingly important in the pharmaceutical industry. In the Hot Melt Extrusion process, the polymer is processed above the glass transition temperature to mix the active component with the thermoplastic binder and / or the polymer on a molecular level.
The most significant benefits of HME processing are the absence of water and solvents, which leads to fewer processing steps and lower manufacturing costs. In addition the short residence time is beneficial for many heat- and shear sensitive drugs and the free volume in the twin screw gives the processor the opportunity to devolatilise the compound in a controlled and reproducible environment.
Because of their excellent mixing behaviour and the degassing possibilities, co-rotating twin-screws are particularly suitable for Hot Melt Extrusion. The modular concept of the Twin Screw Extruder enables the individual adaptation of the processing section to the different requirements. Individual steps such as dispersive mixing, degassing and pressure build-up take place very effectively in this way.
The closely intermeshing screws with their tight, self-wiping profiles eliminate dead zones over the whole length of the process section. The effect: consistently higher degree of process reliability and optimal self-cleaning. Coperion has references in the pharmaceutical field for twin screw extruders in sizes from 18 to 70 mm screw diameter.
Typical applications for Coperion’s twin screw extruders ZSK:
The control of particulate processes and their understanding can be improved by modern measuring techniques. The paper describes the optical probe system Parsum IPP 70 as an example of the modern measuring techniques which is based on the spatial filtering technique (SFT). Measuring principles are the fibre-optical spatial filtering velocimetry and the fibre-optical spot scanning in order to determine simultaneously the size and the velocity of particles. Therefore the measured particle size distributions are chord length distributions which can be recalculated. A calibration is not necessary.
The Parsum IPP 70 is a compact and highly robust measuring system for application as an in-line particle size analyzer for processes involving larger particulate sizes up to 6000 μm. It allows a data rate up to 20,000 particles per second and the system can track continuously a large variety of process parameters. Different options of the measuring system are available: tube length up to 4 m, air supply system for dispersion and cleaning, comprehensive software support, Ex-Zones and pharma solutions.
The application is given for grinding/dosing, agglomeration, fluidized bed processes, mixing and coating, sieving, wet and dry granulation, spray drying. The Parsum IPP 70 is a powerful tool for process control of fluid bed granulation in pharmaceutical industry. The advantages are: increase of process transparency, short response time in the event of process disturbances, continuous control of product quality, full feedback control for automated solutions, no need of samples and laboratory analysis. Results are given by Petrak et al. . Examples show also the ability to prove the model goodness of a fluid bed process by using IPP 70 in-line-SFT [2–4].
To establish a micro fluidic system that covers the whole production process of drug-loaded solid lipid nanoparticles especially high pressure emulsification and dispersion processes must be taken into account. The advantages of micro fluidic systems in a continuous production imply a high surface-to-volume ratio (material and energy transfer) and a narrow residence time distribution (homogeneously defined stresses). Detailed investigation is needed for process understanding and to improve micro channel geometries.
The micro fluidic geometries were designed to selectively expose product flows to different main break-up mechanisms (shear stress, elongational stress, turbulent stress, particle-particle and particle-wall impacts). Within these groups structural modifications were carried out to evaluate their influence on emulsification and dispersion efficiency.
Two formulations (to simulate the dispersion and emulsification process, respectively) were exposed to the specified micro channel geometries (including channel height variation) at different pressures, optionally using multiple homogenisation cycles in addition.
The emulsification process in general shows a decrease in particle size by elevated pressure and higher number of cycles, as expected. Regarding the pressure drop, straight or bent channel geometries show a much lower breakup efficiency compared to either orifice-like or Y-shaped geometries. The latter two types over all show comparable efficiencies. Applying minor structural modifications to several geometries results in significant differences in particle size. As an example, a cascading quadruple orifice geometry shows significantly smaller particle sizes when the flow first interacts with the smallest orifice in comparison to passing the smallest orifice at the end.
The dispersion of solid particles (hydrophilic alumina Alu C) shows similar results although the drop in particle size is less pronounced in these experiments. This is due to the high binding forces between primary particles.
The authors gratefully acknowledge the DFG for financial support of the DFG research group 856 “Mikrosysteme für partikuläre Life-Science-Produkte“ ().
A pharmacokinetic (PK) model describes the absorption, distribution, metabolism and excretion of a pharmaceutical, thus providing, once properly validated, quantitative predictions of the consequences of various dosing regimens. Pharmacological activity might be linked to properties of a time course for a particular compartment (such as half-life or area-under-curve, AUC), or directly modelled by coupling the PK model with a pharmacodynamic (PD) model of the physiological effect of the agent.
Due to the high replication and mutation rates of the human immunodeficiency virus (HIV), which ultimately results in strains resistant to any single agent, a multiple-agent strategy has to be adopted. Highly active anti-retroviral therapy (HAART) uses two or more agents that target different components of the HIV replication cycle, but these agents typically produce adverse side effects in patients. A number of authors have applied techniques from nonlinear control to this problem, but in general the explicit link between the drug dose and the physiological effect, via the PK, is neglected so that the controls derived are continuous in time. In  the control problem is addressed via feedback linearization applied to a PD model of HIV dynamics. A single-compartment PK model is then used to estimate a dosing regime that gives rise to the required continuous control law.
In  a fixed-point approach was taken to determine the doses required to obtain a particular AUC or target profile. Although a constructive method is shown for determining the required dosing scheme, full solution trajectories and their integrals are required. An iterative method for constructing the dosing regime is proposed here that provides the fixed-point solution from  but is computationally easier to implement, being based on the underlying system equations. After each iteration the current dosing scheme is updated based on a linear operator applied to the difference between achieved and desired target vectors.
The iterative method is applied to the coupled PK-PD model from  in order to directly construct a dosing regime, rather than indirectly via a continuous efficacy profile.
The pharmaceutical industry uses million of animals for in-vivo studies to discover or to develop novel pharmaceutics. Time and costs involved and the extrapolation to human physiology of the data obtained are the main difficulties of these studies. The alternative to laboratory animals is the development of invitro and in-silico models (which are physical and mathematical models respectively).
In literature, different in-vitro models are proposed to reproduce the gastrointestinal tract taking in account both the mixing and the biochemical features. However, these models are not able to reproduce closely the real physiology. To describe the drug release in the human body, different kinds of mathematical models (in-silico models) are proposed. Among these, physiologically-based pharmacokinetic models are more complex and complete: the body is divided into compartiments, corresponding to real structures of the body, each with a specific function. Despite their reliability, these models require the fitting of a lot of parameters.
The aims of this work are to realize an in-vitro model reproducing the mechanical and biochemical features of the gastrointestinal tract and to develope (and validate) a novel physiologically-based model incorporating the pharmacokinetic and physiological parameters.
The proposed in-silico model is simple and is characterized by a limited number of parameters. Haematic drug levels after different kind of administrations have been successfully simulated.