Gastrointestinal characterisation and drug solubility determination in animals

OBJECTIVES: To characterise the gastrointestinal (GI) environment in rat, rabbit and pig for the purpose of determining their utility as animal models for drug delivery in humans. METHODS: GI fluid samples were characterised for osmolality, surface tension, pH and buffer capacity. The solubility of two model drugs, mesalazine (ionisable) and prednisolone (unionisable), were also measured and the results were correlated to the physicochemical fluid data. KEY FINDINGS: The solubility of the ionisable drug mesalazine was positively correlated to the GI pH in all three species and was significantly influenced by the pH difference. In contrast, the solubility of the unionisable compound prednisolone was not correlated significantly to the changes in pH, buffer capacity, osmolality or surface tension. In general, the solubility of prednisolone was constant irrespective of the location of the sample in the gut from rabbit and pig; however, an unusual trend was observed for the solubility of prednisolone in rats. CONCLUSIONS: The results suggest that solubility of ionisable drugs or pH-responsive formulations is significantly influenced by the differences in pH along the GI tract and inter-species differences. It was also found that the data on the GI solubility of prednisolone (a neutral compound) in rats might overestimate its true value in humans

From Drug Delivery Systems to Drug Release, Dissolution, IVIVC, BCS, BDDCS, Bioequivalence and Biowaivers

This is a summary report of the conference on drug absorption and bioequivalence issues held in Titania Hotel in Athens (Greece) from the 28(th) to the 30(th) of May 2009. The conference included presentations which were mainly divided into three sections. The first section focused on modern drug delivery systems such as polymer nanotechnology, cell immobilization techniques to deliver drugs into the brain, nanosized liposomes used in drug eluting stents, encapsulation of drug implants in biocompatible polymers, and application of differential scanning calorimetry as a tool to study liposomal stability. The importance of drug release and dissolution were also discussed by placing special emphasis on camptothecins and oral prolonged release formulations. The complexity of the luminal environment and the value of dissolution in lyophilized products were also highlighted. The second session of the conference included presentations on the Biopharmaceutics Classification Scheme (BCS), the Biopharmaceutics Drug Disposition Classification System (BDDCS), and the role of transporters in the classification of drugs. The current status of biowaivers and a modern view on non-linear in vitro-in vivo (IVIVC) correlations were also addressed. Finally, this section ended with a special topic on biorelevant dissolution media and methods. The third day of the conference was dedicated to bioequivalence. Emphasis was placed on high within-subject variability and its impact on study design. Two unresolved issues of bioequivalence were also discussed: the use of generic antiepileptic drugs and the role of metabolites in bioequivalence assessment. Finally, the conference closed with a presentation of the current regulatory status of WHO and EMEA