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26.  Permeability classification of representative fluoroquinolones by a cell culture method 
AAPS PharmSci  2004;6(2):1-6.
This study was undertaken to categorize representative fluoroquinolone drug substance permeability based on the methods outlined in the Food and Drug Administration's biopharmaceutic classification system (BCS) Guidance for Industry. The permeability of ciprofloxacin, levofloxacin, lomefloxacin, and ofloxacin was measured in an in vitro Caco-2 assay with previously demonstrated method suitability. The permeability class and efflux potential were ascertained by comparing test drug results with standard compounds (metoprolol, atenolol, labetalol, and rhodamine-123). All 4 quinolones drugs demonstrated concentration-dependent permeability, indicating active drug transport. In comparing absorptive versus secretive in vitro transport, the tested fluoroquinolones were found to be subject to efflux in varying degrees (ciprofloxacin > lomefloxacin > rhodamine 123 > levofloxacin > ofloxacin). Based on comparison to labetalol, the high permeability internal standard, ciprofloxacin was classified as a low permeability drug, whereas lomefloxacin, levofloxacin, and ofloxacin were classified as high permeability drugs. The in vitro permeability results matched human in vivo data based on absolute bioavailabilities. This laboratory exercise demonstrated the applicability of an in vitro permeability method for classifying drugs as outlined in the BCS Guidance.
PMCID: PMC2751005  PMID: 18465265
permeability; Caco-2; biopharmaceutics classification system; fluoroquinolones
27.  Encapsulation of water-insoluble drug by a cross-linking technique: Effect of process and formulation variables on encapsulation efficiency, particle size, and in vitro dissolution rate 
AAPS PharmSci  2004;6(1):112-119.
Ibuprofen-gelatin micropellets were prepared by the cross-linking technique using formaldehyde. Spherical micropellets having an entrapment efficiency of 65% to 85% were obtained. The effect of core to coat ratio, speed of agitation, temperature, and volume of oil phase was studied with respect to entrapment efficiency, micropellet size, and surface characteristics. Fourier transform infrared spectroscopy and differential scanning calorimetric analysis confirmed the absence of any drug-polymer interaction. X-ray diffraction patterns showed that there is a decrease in crystallinity of the drug. The micromeritic properties of micropellets were found to be slightly changed by changing various processing parameters to give micropellets of good flow property. The in vitro release profile could be altered significantly by changing various processing parameters to give a controlled release of drug from the micropellets. The stability studies of the drug-loaded micropellets showed that the drug was stable at storage conditions of room temperature, 37°C, 25°/60% relative humidity (RH) and 45°/60% RH, for 12 weeks.
PMCID: PMC2750947  PMID: 18465264
ibuprofen; micropellets; gelatin micropellets
28.  β-cyclodextrin complexes of celecoxib: Molecular-modeling, characterization, and dissolution studies 
AAPS PharmSci  2004;6(1):68-76.
Celecoxib, a specific inhibitor of cycloxygenase-2 (COX-2) is a poorly water-soluble nonsteroidal anti-inflammatory drug with relatively low bioavailability. The effect of β-cyclodextrin on the aqueous solubility and dissolution rate of celecoxib was investigated. The possibility of molecular arrangement of inclusion complexes of celecoxib and β-cyclodextrin were studied using molecular modeling and structural designing. The results offer a better correlation in terms of orientation of celecoxib inside the cyclodextrin cavity. Phase-solubility profile indicated that the solubility of celecoxib was significantly increased in the presence of β-cyclodextrin and was classified as AL-type, indicating the 1∶1 stoichiometric inclusion complexes. Solid complexes prepared by freeze drying, evaporation, and kneading methods were characterized using differential scanning calorimetry, powder x-ray diffractometry, and scanning electron microscopy. In vitro studies showed that the solubility and dissolution rate of celecoxib were significantly improved by complexation with β-cyclodextrin with respect to the drug alone. In contrast, freeze-dried complexes showed higher dissolution rate than the other complexes.
PMCID: PMC2750942  PMID: 15198508
celecoxib; β-cyclodextrin; complexation; molecular-modeling; phase solubility; characterization; dissolution rate
29.  Pharmacokinetics of the time-dependent elimination of all-trans-retinoic acid in rats 
AAPS PharmSci  2004;6(1):1-9.
The time-dependent elimination kinetics of all-transretinoic acid (ATRA) has been associated with autoinduction of its metabolism and has led to the hypothesis that rapid development of acquired clinical resistance to ATRA may be prevented by coadministration of metabolic inhibitors. This study in rats was performed to investigate the pharmacokinetics and onset of timedependent elimination of ATRA, with the purpose of establishing an animal model suitable for in vivo preclinical studies of compounds capable of inhibiting ATRA metabolism. After the intravenous (IV) bolus administration of single doses of ATRA (1.60 mg kg−1 and 0.40 mg kg−1), the plasma concentration-time curves showed an accelerated decline at 180 minutes after dosing. The plasma clearance (Cl) of ATRA, determined after IV administration of a second dose (1.60 mg kg−1), at 180 minutes was greater than Cl after a single dose, thus indicating the existence of a time-dependent elimination process detectable 180 minutes after administration of the first dose. Such time-dependent elimination was confirmed by means of an IV constant-rate infusion of 0.48 mg h−1 kg−1 of ATRA during 10 hours. Peak plasma ATRA concentration was achieved at 180 minutes, after which the plasma concentration decreased to reach a much lower apparent steady-state drug concentration at 420 minutes. The area under the plasma concentration-time curve (AUC) obtained after oral administration of a second ATRA dose (1.60 mg kg−1) was ∼8% of the AUC obtained after a single oral dose; consistent with a time-dependent increase in the elimination of ATRA, as was observed after IV administration.
PMCID: PMC2750936  PMID: 18465253
all-trans-retinoic acid; time-dependent elimination; pharmacokinetic model; rat; intravenous administration; oral administration
30.  Hydroxyzine from topical phospholipid liposomal formulations: Evaluation of peripheral antihistaminic activity and systemic absorption in a rabbit model 
AAPS PharmSci  2003;5(4):41-48.
Hydroxyzine, an effective but sedating H1-antihistamine is given orally to treat allergic skin disorders. This study was performed to assess the peripheral H1-antihistaminic activity and extent of systemic absorption of hydroxyzine from liposomes applied to the skin. Using L-α-phosphatidylcholine (PC), small unilamellar vesicles (SUVs) and multilamellar vesicles (MLVs) containing hydroxyzine were prepared. Hydroxyzine in Glaxal Base (GB) was used as the control. Using a randomized, crossover design, each formulation, containing 10 mg of hydroxyzine, was applied to the shaved backs of 6 rabbits (3.08±0.05 kg). Histamine-induced wheal tests and blood sampling were performed at designated time intervals up to 24 hours. Compared with baseline, hydroxyzine from all formulations significantly suppressed histamine-induced wheal formation by 75% to 95% for up to 24 hours. Mean maximum suppression, 85% to 94%, occurred from 2 to 6 hours, with no differences among the formulations. The areas of plasma hydroxyzine concentration versus time area under the curve (AUCs) from PC-SUV and PC-MLV, 80.1±20.8 and 78.4±33.9 ng/mL/h, respectively, were lower than that from GB, 492±141 ng/mL/h (P<.05) over 24 hours. Plasma concentrations of cetirizine arising in-vivo as the active metabolite of hydroxyzine, from PC-SUV, PC-MLV, and GB, were similar with AUCs of 765±50, 1035±202, and 957±227 ng/mL/h, respectively (P<.05). Only 0.02% to 0.06% of the initial hydroxyzine dose remained on the skin after 24 hours. In this model, hydroxyzine from SUV and MLV had excellent topical H1-antihistaminic activity, and minimal systemic exposure occurred. Cetirizine formed in-vivo contributed to some of H1-antihistaminic activity.
PMCID: PMC2750990  PMID: 15198516
hydroxyzine; L-α-phosphatidylcholine; liposomes; antihistamine; skin; rabbit
31.  Amphiphilic star-like macromolecules as novel carriers for topical delivery of nonsteroidal anti-inflammatory drugs 
AAPS PharmSci  2003;5(4):1-12.
The objective of this study was to evaluate amphiphilic star-like macromolecules (ASMs) as a topical drug delivery system. Indomethacin, piroxicam, and ketoprofen were individually encapsulated into the ASMs using coprecipitation. The effects of the ASMs on percutaneous permeation of nonsteroidal anti-inflammatory drugs (NSAIDs) across full thickness, hairless mouse skin were evaluated in vitro using modified Franz diffusion cells. In addition, solubility and in vitro release experiments were performed to characterize ASMs behavior in aqueous media. Poly(ethylene glycol) (PEG) and Pluronic P-85 were used as polymer controls to compare the role of PEG and amphiphilic behavior in the ASMs. In vitro release experiments indicated that ASMs can delay drug release (P⋖05), whereas solubility measurements showed that ASMs can increase NSAIDs aqueous solubility (P⋖05). Percutaneous permeation studies revealed that ASMs decreased both flux and Q24 of drugs compared with the control (P⋖10). Skin pretreatment studies with ASM-containing solution before drug application demonstrated that pretreatment similarly influenced NSAID percutaneous permeation. In conclusion, ASMs likely slow drug permeation through 2 mechanisms, delayed drug diffusion from its core and skin dehydration by its shell. Thus, ASMs may be useful for delayed dermal delivery or prevention of compound permeation through the skin (eg, sunscreens, N,N-diethyl-m-toluamide [DEET]) from aqueous formulations.
PMCID: PMC2750988  PMID: 15198514
topical drug delivery; NSAIDs; polymeric micelle; permeation; drug release
32.  Wet granulation fine particle ethylcellulose tablets: Effect of production variables and mathematical modeling of drug release 
AAPS PharmSci  2003;5(2):48-60.
In the present study, the applicability of fine particle ethylcellulose (FPEC) to produce matrix tablets by a wet granulation technique was evaluated. The effect of various formulation and process variables, such as FPEC content, hardness of the tablet, and solubility of the drug, on the release of drug from these tablets was examined. Tablets were prepared by wet granulation of drug and FPEC in an appropriate mass ratio. Theophylline, caffeine, and dyphylline were selected as nonionizable model drugs with solubilities from 8.3 to 330 mg/mL at 25°C. Ibuprofen, phenylpropanolamine hydrochloride, and pseudoephedrine hydrochloride were selected as ionizable drugs with solubilities from 0.1 to 2000 mg/mL at 25°C. Drug release studies were conducted in 37°C water with UV detection. As the FPEC content and the hardness of the tablets increased, the release rate of the drug decreased. The drug release rate increased with an increase in the solubility of the drug. Model equations, intended to elucidate the drug release mechanism, were fitted to the release data. Parameters were generated and data presented by SAS software. The Akaike Information Criterion was also considered to ascertain the best-fit equation. Fickian diffusion and polymer relaxation were the release mechanisms for nonionizable and ionizable drugs.
PMCID: PMC2751521  PMID: 12866940
fine particle ethylcellulose; wet granulation; ionizable drugs; nonionizable drugs; Fickian diffusion; polymer relaxation
33.  Evaluation of novel particles as pulmonary delivery systems for insulin in rats 
AAPS PharmSci  2003;5(2):10-20.
The purpose of the study was to evaluate the influence of calcium phosphate (CAP) and polyethylene glycol (PEG) particles on the systemic delivery of insulin administered by the pulmonary route. Two methods of pulmonary delivery were employed: intratracheal instillation and spray instillation. Insulin-CAP-PEG particles in suspension (1.2 U/kg, 110–140 μL) were administered to the lungs of fasted rats by intratracheal instillation (INCAPEG) or spray instillation (SINCAPEG). Control treatments consisted of insulin solution (1.2 U/kg) by intratracheal instillation, spray instillation, and subcutaneous administration (SC). Plasma concentrations of insulin and glucose were determined by chemiluminescence and colorimetric methods, respectively. Data were analyzed by compartmental and non-compartmental methods, and pharmacokinetic (PK) and pharmacodynamic (PD) parameters of insulin disposition were determined. PK analysis suggested that insulin administered in particles had a longer half-life, a longer mean residence time, and a smaller rate of elimination than insulin in solution. In addition, insulin bioavailability after SINCAPEG was 1.8-fold that of insulin solution administered SC. PD analysis showed that smaller areas under the effect curve and, conversely, larger areas above the effect curve were obtained after INCAPEG in comparison to insulin solution. The magnitude of this effect was increased after SINCAPEG. The presence of CAP-PEG particles appears to positively influence the disposition of insulin administered to the lungs of Sprague-Dawley rats. Spray instillation appears to be a more efficient method of delivering insulin to the lungs of rats than intratracheal instillation.
PMCID: PMC2751517  PMID: 12866936
pulmonary delivery; insulin; CAP-PEG particles; pharmacokinetics; pharmacodynamics
34.  Development of a multidose formulation for a humanized monoclonal antibody using experimental design techniques 
AAPS PharmSci  2003;5(2):1-9.
The purpose of this study was to identify optimal preservatives for a multidose formulation of a humanized monoclonal antibody using experimental design techniques. The effect of antimicrobial parenteral preservatives (benzyl alcohol, chlorobutanol, methyl paraben, propylparaben, phenol, and m-cresol) on protein stability was assessed using size-exclusion chromatography, differential scanning calorimetry, right-angle light scattering, UV spectroscopy, and potency testing using a cell-based fluorescence-activated cell sorting method. A quick, cost-effective preservative screening test was designed. Combinations of preservatives were examined using an I-optimal experimental design. The protein was most stable in the presence of methylparaben and propylparaben, and was compatible with benzyl alcohol and chlorobutanol at low concentrations. Phenol and m-cresol were not compatible with the protein. The I-optimal experimental design indicated that as an individual preservative, benzyl alcohol was promising. The model also indicated several effective combinations of preservatives that satisfied the antimicrobial efficacy and physical stability constraints. The preservative screening test and the experimental design approach were effective in identifying optimal concentrations of antimicrobial preservatives for a multidose protein formulation; (1) benzyl alcohol, and (2) the combination of methylparaben and chlorobutanol were screened as potential candidates to satisfy the regulatory requirements of various preservative efficacy tests.
PMCID: PMC2751516  PMID: 12866935
multidose formulation; preservative; experimental design; monoclonal antibody; protein
35.  A mucoadhesive, cyclodextrin-based vaginal cream formulation of itraconazole 
AAPS PharmSci  2003;5(1):50-54.
The development of vaginal medications, especially antifungal medications, requires that the drug is solubilized as well as retained at or near the mucosa for sufficient periods of time to ensure adequate bioavailability. Itraconazole is a broad-spectrum antifungal agent, which has been used for some time orally and intravenously but for which a vaginal formulation has not yet been developed. We present here a novel itraconazole formulation intended for vaginal use based on hydroxypropyl-β-cyclodextrin (HPβCD), a functional excipient that increases drug solubility and generates a mucoadhesive system in the presence of other ingredients. An aqueous phase was prepared by solubilizing itraconazole with HCl in the presence of propylene glycol and then adding an aqueous solution of HPβCD. After pH adjustment, the itraconazole/HPβCD solution was added to the oil phase (paraffin oil, trihydroxystearate, and cetyl dimethicon copolyol) and the desired cream containing 1%, 2%, and 2.5% drug obtained by homogenization. Primary irritation studies and subchronic toxicity studies using a rabbit vaginal model indicated that the formulation was safe, well tolerated, and retained in the vaginal space. Clinical investigations indicated that application of 5 g of a 2% cream was very well tolerated and itraconazole was not systemically absorbed. Additional studies in women found that the itraconazole cream was highly effective in reducing or eliminating fungal cultures with few adverse effects. These studies suggested that an HPβCD-based, emulsified wax cream formulation was a useful and effective dosage form for treating vaginal candidiasis.
PMCID: PMC2751473  PMID: 12713277
Itraconazole; vaginal; cyclodextrin; mucoadhesive; toxicity; clinical investigation; candidiasis
36.  Pharmacodynamic modeling of chemotherapeutic effects: Application of a transit compartment model to characterize methotrexate effects in vitro 
AAPS PharmSci  2002;4(4):212-222.
The time course of chemotherapeutic effect is often delayed relative to the time course of chemotherapeutic exposure. In many cases, this delay is difficult to characterize mathematically through the use of standard pharmacodynamic models. In the present work, we investigated the relationship between methotrexate (MTX) exposure and the time course of MTX effects on tumor cell growth in culture. Two cancer cell lines, Ehrlich ascites cells and sarcoma 180 cells, were exposed for 24 hours to MTX concentrations that varied more than 700-fold (0.19–140 μg/mL). Viable cells were counted on days 1, 3, 5, 7, 9, 11, 13, 15, 17, 20, 22, and 24 for Ehrlich ascites cells and on days 1, 2, 3, 5, 7, 9, 11, 13, 14, 15, 17, 19, and 21 for sarcoma 180 cells, through the use of a tetrazolium assay. Although MTX was removed 24 hours after application, cell numbers reached nadir values more than 100 hours after MTX exposure. Data from each cell line were fitted to 3 pharmacodynamic models of chemotherapeutic cell killing: a cell cycle phase-specific model, a phase-nonspecific model, and a transit compartment model (based on the general model recently reported by Mager and Jusko, Clin Pharmacol Ther. 70:210–216, 2001). The transit compartment model captured the data much more accurately than the standard pharmacodynamic models, with correlation coefficients ranging from 0.86 to 0.999. This report shows the successful application of a transit compartment model for characterization of the complex time course of chemotherapeutic effects; such models may be very useful in the development of optimization strategies for cancer chemotherapy.
PMCID: PMC2751331  PMID: 12646013
methotrexate; cell growth inhibition; modeling; chemotherapeutic effect; transit compartment model
37.  Role of plasma lipoproteins in modifying the toxic effects of water-insoluble drugs: Studies with cyclosporine A 
AAPS PharmSci  2002;4(4):95-101.
Lipoproteins are a heterogeneous population of macromolecular aggregates of lipids and proteins that are responsible for the transport of lipids through the vascular and extravascular fluids from their site of synthesis or absorption to peripheral tissues. Lipoproteins are involved in other biological processes as well, including coagulation and tissue repair, and serve as carriers of a number of hydrophobic compounds within the systemic circulation. It has been well documented that disease states (eg, AIDS, diabetes, cancer) significantly influence circulating lipoprotein content and composition. Therefore, it appears possible that changes in the lipoprotein profile would affect not only the ability of a compound to associate with lipoproteins but also the distribution of the compound within the lipoprotein subclasses. Such an effect could alter the pharmacokinetics and pharmacological action of the drug. This paper reviews the factors that influence the interaction of one model hydrophobic compound, cyclosporine A, with lipoproteins and the implications of altered plasma lipoprotein concentrations on the pharmacological behavior of this compound.
PMCID: PMC2751319  PMID: 12646002
38.  Novel system to investigate the effects of inhaled volume and rates of rise in simulated inspiratory air flow on fine particle output from a dry powder inhaler 
AAPS PharmSci  2002;4(2):7-12.
This study evaluated the effect of inhaled volume and simulated inspiratory flow rate ramps on fine particle output from dry powder inhalers (DPIs). A simple, robust system was developed to account for “rate of rise” (ramp) effects while maintaining a constant air flow through a multi-stage liquid impinger (MSLI), used for sizing the emitted particles. Ramps were programmed to reach 30 and 60 L/min over 100 milliseconds; 500 milliseconds; and 1, 2, and 3 seconds. Rotahaler was chosen as the test DPI. Testing was done with simulated inhalation volumes of 2 L and 4 L. Testing was also carried out using the USP apparatus 4. At 30 L/min, for a 2 L volume, the amount of drug exiting the device in fine particle fraction (FPF) increased from 2.33 μg to 6.04 μg from the 3-second ramp to the 100-millisecond ramp, with 11.64 μg in FPF for the USP (no ramp) method. At the same flow rate, for a 4 L volume, FPF increased from 2.23 μg to 8.45 μg, with 10.25 μg for the USP method. At 60 L/min, similar trends were observed. In general, at both flow rates, an increase in FPF was noted going from the shallowest to the steepest ramp. However, there were no significant differences in FPF when a 2 L inhaled volume was compared with a 4 L volume at each flow rate. Overall, these data suggest that the existing USP apparatus may overestimate FPF at flow rates lower than those recommended by the USP.
PMCID: PMC2751291  PMID: 12102620
Dry Powder Inhalers; Ramps In Vitro Testing; Fine Particle Output; Inhaled Volume
39.  Influence of drug release properties of conventional solid dosage forms on the systemic exposure of highly soluble drugs 
AAPS PharmSci  2001;3(3):86-92.
This study was designed to theoretically investigate the influence of drug release properties, characterized by the disintegration of a solid dosage form and dissolution of drug particles, on the systemic exposure of highly soluble drugs in immediate release products. An absorption model was developed by considering disintegration of a solid dosage form, dissolution of drug particles, gastrointestinal transit flow, and intestinal absorption processes. The absorption model was linked to a conventional pharmacokinetic model to evaluate the effect of disintegration and dissolution on the peak exposure (Cmax) and total exposure of area under the curve (AUC). Numerical methods were used to solve the model equations. The simulations show that the effect of disintegration of a dosage form and dissolution of drug particles depend on the permeability of a drug, with a low-permeability drug having a greater effect. To provide similar exposure to an oral solution formulation, a solid dosage form containing a low-permeability drug would need to dissolve more rapidly than a solid dosage form containing a high-permeability drug. It was shown theoretically for poorly permeable drugs that the disintegration rate constant has to be greater than 9 hour−1 (equivalent to approximately 90% in 30 minutes) to make both AUC and Cmax ratios higher than .9, ensuring the confidence interval of .80 to 1.25. The rapid in vitro release requirement of at least 85% dissolved in 30 minutes is sufficient for highly soluble and highly permeable drugs. However, for highly soluble and poorly permeable drugs, the appropriate in vitro release requirement seems to be 90% dissolved in 30 minutes.
PMCID: PMC2751019  PMID: 11741275
Small intestinal transit; dissolution; disintegration; absorption modeling; bioequivalence
40.  Low molecular weight protamine as nontoxic heparin/low molecular weight heparin antidote (III): Preliminary in vivo evaluation of efficacy and toxicity using a canine model 
AAPS PharmSci  2001;3(3):24-31.
Heparin employed in cardiovascular surgeries often leads to a high incidence of bleeding complications. Protamine employed in heparin reversal, however, can cause severe adverse reactions. In an attempt to address this clinical problem, we developed low molecular weight protamine (LMWP) as a potentially effective and less toxic heparin antagonist. A homogeneous 1880-d peptide fragment, termed LMWP-TDSP5 and containing the amino acid sequence of VSRRRRRRGGRRRR was derived directly from protamine by enzymatic digestion of protamine with thermolysin. In vitro studies demonstrated that TDSP5 was capable of neutralizing various anticoagulant functions of both heparin and commercial low molecular weight heparin preparations. In addition, TDSP5 exhibited significantly reduced crossreactivity toward mouse sera containing antiprotamine antibodies. TDSP5 showed a decrease in its potential in activating the complement system. All of these findings suggested the possibility of markedly reduced protamine toxicity for TDSP5.
In this article, we conducted preliminary in vivo studies to further demonstrate the feasibility and utility of using LMWP as a nontoxic clinical protamine substitute. Dogs were chosen as test animals because they were known to magnify the typical human response to protamine. By using a full spectra of biological and clinical assays for heparin, including the anti-IIa and anti-Xa chromogenic assays and the activated partial, thromboplastin time and TCT clotting assays, TDSP5 showed that it could completely neutralize all these different anticoagulant functions of heparin in dogs. Although administration of protamine in dogs produced a significant reduction in mean arterial blood pressure (−14.9 mm Hg) and elevation in pulmonary artery systolic pressure (+5.0 mm Hg), the use of TDSP5 in dogs did not elicit any statistically significant change in any of the variables measured. Furthermore, the use of LMWP also significantly reduced the protamine-induced transient thrombocytopenic and granulocytopenic responses. The white blood cell counts and platelet counts decreased to 82.1% and 60.0% of baseline, respectively, in dogs given intravenous protamine compared to 97.8% and 88.6% of baseline in dogs receiving TDSP5. These preliminary findings indicated that LMWP could potentially provide an effective and safe means to control both heparin- and protamine-induced complications.
PMCID: PMC2751014  PMID: 11741270
Heparin Neutralization; Protamine Toxicity; aPTT/TCT Heparin Clotting Assays; Anti-IIa Anti-Xa Chromogenic Assays; Hemodynamic/Hematologic Responses
41.  Application of confocal laser scanning microscopy in characterization of chemical enhancers in drug-in-adhesive transdermal patches 
AAPS PharmSci  2001;4(1):11-18.
The purpose of this study was to evaluate the application of confocal laser scanning microscopy (CLSM) in the examination of the embedment and the release characteristics of chemical permeation enhancers from transdermal drug delivery systems (TDDSs) of the “drug-in-adhesive” type. The enhancer lauric acid and a lauric acid fluorescing probe of the Bodipy type were incorporated into TDDSs consisting of an acrylic, a polyisobutylene, or a silicone polymer adhesive. Three-dimensional confocal images of the distribution were obtained before and during release into an aqueous medium. The images showed that the lauric acid fluorescing probe was homogeneously embedded in all the adhesives except for 1 polyisobutylene. The release profiles and release rate constants of the lauric acid fluorescing probe were consistent with data from a release study of lauric acid performed using conventional measurements of the released amounts. This indicated that lauric acid was distributed in a homogeneous manner. Furthermore, it was possible to illustrate the mechanics of the diffusion process inside the TDDS and compare these patterns with theoretically drawn profiles, based on Ficks law of diffusion. CLSM was demonstrated to be an excellent tool to study how enhancers are incorporated and diffuse into a TDDS.
PMCID: PMC2751288  PMID: 12049487
confocal laser scanning; microscopy; chemical enhancers; diffusion; drug-in-adhesive patches; release mechanism
42.  Maltodextrin-based proniosomes 
AAPS PharmSci  2001;3(1):1-8.
Niosomes are nonionic surfactant vesicles that have potential applications in the delivery of hydrophobic or amphiphilic drugs. Our lab developed proniosomes, a dry formulation using a sorbitol carrier coated with nonionic surfactant, which can be used to produce niosomes within minutes by the addition of hot water followed by agitation. The sorbitol carrier in the original proniosomes was soluble in the solvent used to deposit surfactant, so preparation was tedious and the dissolved sorbitol interfered with the encapsulation of one model drug. A novel method is reported here for rapid preparation of proniosomes with a wide range of surfactant loading. A slurry method has been developed to produce proniosomes using maltodextrin as the carrier. The time required to produce proniosomes by this simple method is independent of the ratio of surfactant solution to carrier material and appears to be scalable. The flexibility of the proniosome preparation method would allow for the optimization of drug encapsulation in the final formulation based on the type and amount of maltodextrin. This formulation of proniosomes is a practical and simple method of producing niosomes at the point of use for drug delivery.
PMCID: PMC2751233  PMID: 11741252
Niosomes; Proniosomes; Maltodextrin; Slurry method
43.  No evidence for the involvement of the multidrug resistance-associated protein and/or the monocarboxylic acid transporter in the intestinal transport of fluvastatin in rats 
AAPS PharmSci  2000;2(3):62-68.
Fluvastatin, an amphiphilic anion, shows a nonlinear increase in effective intestinal permeability (Peff) with increasing lumenal concentrations in rats. The main objective of this study was to investigate whether or not this observation could be attributed to an efflux-mediated transport by the multidrug resistance-associated protein (MRP). In parallel, we investigated the possible involvement of the monocarboxylic acid transporter (MCT) in the rapid intestinal absorption of fluvastatin. Single-pass perfusions were performed in the ileum and colon of the rat, with and without the presence of well-established inhibitors/substrates for the MRP (probenecid) and the MCT (nicotinic acid). The results suggest that neither the MRP nor the MCT are involved to any significant extent in the absorption process of fluvastatin in the rat intestine. Thus, the previously reported concentration-dependent Peff of fluvastatin in these intestinal regions of the rat is probably not attributable to saturation of any efflux mediated by MRP.
PMCID: PMC2761137  PMID: 11741242
Fluvastatin; Drug Absorption; Intestinal Efflux; Multidrug Resistance-Associated Protein; Monocarboxylic Acid Transporter
44.  Recovery of human skin impedance in vivo after lontophoresis: Effect of metal ions 
AAPS PharmSci  2000;2(3):38-44.
The objective of this study was to investigate the effect of the counter-ion (cation) on the recovery of human skin impedance after iontophoresis in vivo. A series of metal chloride aqueous solutions (NaCl, KCl, CaCl2, and MgCl2) was investigated: first at the same concentration (133 mmol/L) and then at the same ionic strength as a NaCl solution at 133 mmol/L. The influence of hydration alone was also examined as a control. The recovery of human skin impedance was followed in the frequency range 1–1,000 Hz, over a 30-minute period after iontophoresis during which 3 impedance spectra were recorded. The results revealed that at t=30 minutes post-iontophoresis, skin impedance was approximately 3 times greater than the value immediately after the cessation of current passage. However, the results showed that the nature of the cation had no effect on recovery, regardless of whether the ions were at the same concentration or at an equivalent ionic strength. A simple parallel RC-equivalent circuit model for skin was used to determine the resistive (R) and capacitive (C) contributions to skin impedance. An analysis of variance on the calculated R and C values did not show any differences between the electrolytes used at the 2 different ionic strengths.
PMCID: PMC2761134  PMID: 11741239
45.  Targeted prodrug design to optimize drug delivery 
AAPS PharmSci  2000;2(1):48-58.
Classical prodrug design often represents a nonspecific chemical approach to mask undesirable drug properties such as limited bioavailability, lack of site specificity, and chemical instability. On the other hand, targeted prodrug design represents a new strategy for directed and efficient drug delivery. Particularly, targeting the prodrugs to a specific enzyme or a specific membrane transporter, or both, has potential as a selective drug delivery system in cancer chemotherapy or as an efficient oral drug delivery system. Site-selective targeting with prodrugs can be further enhanced by the simultaneous use of gene delivery to express the requisite enzymes or transporters. This review highlights evolving strategies in targeted prodrug design, including antibody-directed enzyme prodrug therapy, genedirected enzyme prodrug therapy, and peptide transporter-associated prodrug therapy.
PMCID: PMC2751001  PMID: 11741222
46.  Comparison of the rates of deamidation, diketopiperazine formation, and oxidation in recombinant human vascular endothelial growth factor and model peptides 
AAPS PharmSci  2000;2(1):42-47.
In this work, we examine the way in which stability information obtained from studies on small model peptides correlates with similar information acquired from a protein. The rates of deamidation, oxidation, and diketopiperazine reactions in model peptide systems were compared to those of recombinant human vascular endothelial growth factor (rhVEGF). The N-terminal residues of rhVEGF, a potent mitogen in angiogenesis, are susceptible to the aforementioned reactions. The degradation of the peptides L-Ala-L-Pro-L-Met (APM) and Gly-L-Gsn-L-His-L-His (GQNHH), residues 1–3 and 8–12 of rh VEGF, respectively, and rhVEGF were examined at pH 5 and 8 at 37°C. Capillary electrophoresis and high-performance liquid chromatography (HPLC) stability-indicating assays were developed to monitor the degradation of the penta- and tripeptides, respectively. The degradation of rhVEGF was determined by tryptic mapping and quantified by RP-HPLC. The rates of degradation of both peptides and the protein followed apparent first-order kinetics and increased with increasing pH. The tripeptide APM underwent diketopiperazine formation (Ala-Prodiketopiperazine) and oxidation of the Met residue, whereas the pentapeptide GQNHH degraded via the deamidation pathway. The results indicate that the rates of deamidation and oxidation of the protein are comparable to those observed in the model peptides at both pH values. However, the rate of the diketo-piperazine reaction was slower in the protein than in the model peptide, which may be the result of differences in the cis-trans equilibrium of the X-Pro peptide bonds in the 2 molecules.
PMCID: PMC2751000  PMID: 11741221
47.  A novel in vitro release method for submicron-sized dispersed systems 
AAPS PharmSci  1999;1(3):32-40.
Sink conditions are often violated when using conventional release methods for dispersed systems. A novel reverse dialysis bag method was designed to overcome this problem. Model drug transport rates from submicron emulsions obtained using the conventional diffusion cell method and this novel method were compared. In the side-by-side diffusion cell method, emulsions were placed in the donor chamber and surfactant/buffer solutions in the receiver chamber. In the novel dialysis bag method, emulsions were diluted infinitely in the donor phase and surfactant/buffer solutions were placed in the receiver phase (dialysis bags). Slow release rates and linear release profiles were obtained using the side-by-side diffusion cell method apparently due to limited model drug solubility in the donor chamber resulting in violation of sink conditions. Biphasic release profiles were obtained using the dialysis bag method apparently due to an initial rapid release of free and micellar solubilized model drug from the donor to the receiver chambers followed by slow release from the oil droplets. Using both release methods, an initial increase and latter decrease in release rates were observed with increase in surfactant concentration. The initial increase was considered to be due to a decrease in the model drug oil-in-water partition coefficients and the subsequent decrease in release rates was due to micellar shape change (spheres to rods) causing a decrease in diffusion rates. Sink conditions were violated using the side-by-side diffusion cell method but were maintained in the dialysis bag method since emulsions were diluted infinitely in the donor phase.
PMCID: PMC2761125  PMID: 11741207
dialysis bag; submicron emulsions; in vitro release; dispersed systems; sink conditions
48.  Activity and kinetics of dissociation and transfer of amphotericin B from a novel delivery form 
AAPS PharmSci  1999;1(3):21-31.
Recently it has been demonstrated that moderate heat treatment of Amphotericin B/deoxycholate solutions (HAmB-DOC) leads to a therapeutically interesting supramolecular rearrangement that can be observed by significant changes in light scattering, CD, and absorbance. In this study, we continue the investigation of the physical properties of this new form by evaluating the activity and kinetics of dissociation and dispersion of HAmB-DOC and AmB-DOC in saline, serum, and in model mammalian or fungal lipid biomimetic membrane vesicles. Stopped-flow spectrophotometry combined with singular value decomposition (SVD) and global analysis were used to resolve the components of this process. The dissociation kinetics for both states are complex, requiring multiexponential fits, vet in most cases SVD indicates only two significant changing species representing the monomer and the aggregate. The kinetic mechanism could involve dissociation of monomers from coexisting spectroscopically similar but structurally distinct aggregates or sequential rearrangements in supramolecular structure of aggregates. Rate constants and amplitudes of dissociation from aggregates to monomer in buffer, whole serum, 10% cholesterol, and ergosterol membrane vesicles are generally greater for AmB-DOC, demonstrating its greater kinetic instability. In addition, at comparable low concentrations, HAmB-DOC and AmB-DOC are nearly equally active at promoting cation selective permeability in ergosterol-containing membranes; however, HAmB-DOC is much less active against mammalian mimetic cholesterol-containing vesicles, despite a higher level of self-association, supporting previous observations that there exists a specific “toxic aggregate” structure.
PMCID: PMC2761124  PMID: 11741206
49.  Kinetic modeling of plasmid DNA degradation in rat plasma 
AAPS PharmSci  1999;1(3):15-20.
A major obstacle in gene delivery is the transport of intact plasmid DNA (pDNA) to target sites. We sought to investigate the kinetic processes underlying the degradation of pDNA in a rat plasma model, as this is one of the main components responsible for the clearance of pDNA after intravenous administration. We further sought to construct a complete kinetic model to describe the degradation of all three topoforms (supercoiled, open circular, and linear) of pDNA in a rat plasma model. Supercoiled pDNA was incubated in isolated rat plasma at 37°C in vitro. At various time points, the plasma was assayed by electrophoresis for the amounts of supercoiled, open circular, and full-length linear pDNA remaining. The calculated amounts remaining were fit to linear differential equations describing this process. In this model, pDNA degradation is considered to be a unidirectional process, with supercoiled degrading to open circular and then to the linear topoform. The calculated kinetic parameters suggested that supercoiled pDNA degrades in rat plasma with a half-life of 1.2 minutes, open circular pDNA degrades with a half-life of 21 minutes, and linear pDNA degrades with a half-life of 11 minutes. Complexation of pDNA with liposomes resulted in a portion of the supercoiled plasmid remaining detectable through 5.5 hours.
PMCID: PMC2761123  PMID: 11741205
50.  Assuring quality and performance of sustained and controlled release parenterals: EUFEPS workshop report 
AAPS PharmSci  2004;6(1):100-111.
This is a summary report of the workshop, organized by the European Federation of Pharmaceutical Scientists in association with the American Association of Pharmaceutical Scientists, the European Agency for the Evaluation of Medicinal Products, the European Pharmacopoeia, the US Food and Drug Administration and the United States Pharmacopoeia, on “Assuring Quality and Performance of Sustained and Controlled Release Parenterals” held in Basel, Switzerland, February 2003. Experts from the pharmaceutical industry, regulatory authorities and academia participated in this workshop to review, discuss and debate formulation, processing and manufacture of sustained and controlled release parenterals, and identify critical process parameters and their control. This workshop was a follow-up workshop to a previous workshop on Assuring Quality and Performance of Sustained and Controlled Release Parenterals that was held in Washington, DC in April 2001. This report reflects the outcome of the Basel 2003 meeting and the advances in the field since the Washington, DC meeting in 2001. As necessary, the reader is referred to the report on the 2001 meeting. Areas were identified at the 2003 Basel meeting where research is needed in order to understand the performance of these drug delivery systems and to assist in the development of appropriate testing procedures. Recommendations were made for future workshops and meetings.
PMCID: PMC2750946  PMID: 18465263

Results 26-50 (184)