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1.  An Automated System for Monitoring and Regulating the pH of Bicarbonate Buffers 
AAPS PharmSciTech  2013;14(2):517-522.
The bicarbonate buffer is considered as the most biorelevant buffer system for the simulation of intestinal conditions. However, its use in dissolution testing of solid oral dosage forms is very limited. The reason for this is the thermodynamic instability of the solution containing hydrogen carbonate ions and carbonic acid. The spontaneous loss of carbon dioxide (CO2) from the solution results in an uncontrolled increase of the pH. In order to maintain the pH on the desired level, either a CO2 loss must be completely avoided or the escaped CO2 has to be replaced by quantitative substitution, i.e. feeding the solution with the respective amount of gas, which re-acidifies the buffer after dissociation. The present work aimed at the development of a device enabling an automatic pH monitoring and regulation of hydrogen carbonate buffers during dissolution tests.
doi:10.1208/s12249-013-9933-5
PMCID: PMC3666009  PMID: 23468339
bicarbonate media; hydrogen carbonate buffer; modified release; physiological buffers; biorelevant dissolution
2.  An Oral-Controlled Release Drug Delivery System for Liquid and Semisolid Drug Formulations 
AAPS PharmSciTech  2011;12(4):1183-1185.
A novel oral drug delivery system for the controlled release of liquid drugs, drug solutions, and semisolid drug preparations is presented that is utilizing the constant vapor pressure of liquefied gas. The system is equipped with a capillary as an element determining the drug delivery rate and contains a liquefied propellant with a suitable boiling point below human body temperature. In the dissolution studies, polyacrylate gels of different viscosities containing paracetamol as model drug were used. Zero-order release kinetics was obtained. The release rates were dependent on the gel viscosity. Besides, by gel viscosity, the drug release rates could also be modified by changing the propellant type and the capillary parameters such as length or diameter. Accordingly, the new system enables a wide range of drug delivery kinetics which can be modified in a case-by-case basis in order to match the desired drug delivery characteristics.
doi:10.1208/s12249-011-9689-8
PMCID: PMC3225522  PMID: 21918919
controlled delivery of liquids; controlled release; extended release; oral drug delivery system

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