The aim of the present study was to use gastrointestinal simulation technology and in vitro-in vivo correlation (IVIVC) as tools to investigate a possible extension of biowaiver criteria to BCS class II drugs using carbamazepine (CBZ) as a candidate compound. Gastrointestinal simulation based on the advanced compartmental absorption and transit model implemented in GastroPlus was used. Actual in vitro and in vivo data generated in CBZ bioequivalence studies were used for correlation purposes. The simulated plasma profile, based on the CBZ physicochemical and pharmacokinetic properties, was almost identical with that observed in vivo. Parameter sensitivity analysis (PSA) indicated that the percent of drug absorbed is relatively insensitive to the variation of the input parameters. Additionally, plasma concentration-time profiles were simulated based on dissolution profiles observed under the different experimental conditions. Regardless of the differences observed in vitro, the predicted pharmacokinetic profiles were similar in the extent of drug exposure (AUC) while there were certain differences in parameters defining the drug absorption rate (C(max)t(max)). High level A IVIVC was established for the pooled data set (r = 0.9624), indicating that 1% SLS may be considered as the universal biorelevant dissolution medium for both the IR and CR CBZ tablets. The proposed methodology involving gastrointestinal simulation technology and IVIVC suggests that there is a rationale for considering CBZ biowaiver extension and introduction of the wider dissolution specifications for CBZ immediate release tablets.

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Two oil-in-water formulations, containing equal amounts of apigenin-enriched chamomile flower extracts, for potential use as topical antiinflammatory agents, were prepared and their physicochemical properties evaluated. A pilot clinical study was then carried out to assess patient acceptability and efficacy. The creams were either non-liposomal or liposomal. The liposomal formulations were more viscous, thus producing superior release characteristics in vitro. The clinical study also showed that the liposomal creams were, as antiinflammatory agents, slightly more effective in vivo than the non-liposomal formulations. These results suggest that there is scope for the further development of even more effective and safer alternatives to corticosteroids.

The Biopharmaceutics Classification System (BCS) represents the framework for predicting the intestinal drug absorption based on its solubility and intestinal permeability. Recent research has lead to the use of in vitro tests to waive additional in vivo bioequivalence studies for some pharmaceutical products (i.e., biowaiver). The current regulations permit waivers for BCS Class I (highly soluble/highly permeable) drug substances, which represent up to 25% of the drugs. Efforts in both the science and regulatory bodies are being made to extend biowaivers to certain Class II and III products, which would represent more than 50% of all drugs coming to the market. The aim of this study was to investigate the influence of experimental conditions on metformin hydrochloride (CAS 1115-70-4) release from two immediate-release tablet formulations with proven bioequivalence and justify the biowaiver request for dissolution profile similarity in three pH media. The results obtained indicate that differences in drug dissolution observed in vitro were not reflected in vivo. Such data support the existing idea that BCS Class III drugs are eligible biowaiver candidates, even if a very rapid dissolution criterion is not fulfilled.

The aim of this study was to investigate the influence of experimental conditions on levothyroxine sodium release from two immediate-release tablet formulations which narrowly passed the standard requirements for bioequivalence studies. The in vivo study was conducted as randomised, single-dose, two-way cross-over pharmacokinetic study in 24 healthy subjects. The in vitro study was performed using various dissolution media, and obtained dissolution profiles were compared using the similarity factor value. Drug solubility in different media was also determined. The in vivo results showed narrowly passing bioequivalence. Considering that levothyroxine sodium is classified as Class III drug according to the Biopharmaceutics Classification System, drug bioavailability will be less sensitive to the variation in its dissolution characteristics and it can be assumed that the differences observed in vitro in some of investigated media probably do not have significant influence on the absorption process, as long as rapid and complete dissolution exists. The study results indicate that the current regulatory criteria for the value of similarity factor in comparative dissolution testing, as well as request for very rapid dissolution (more than 85% of drug dissolved in 15 min), are very restricted for immediate-release dosage forms containing highly soluble drug substance and need further investigation. The obtained results also add to the existing debate on the appropriateness of the current bioequivalence standards for levothyroxine sodium products.