Comparative bioavailability of oral dosage forms of oxazepam--correlation with in vitro dissolution rate

Four oxazepam tablet preparations and a suspension of micronized oxazepam in water were given to healthy, fasting volunteers in a comparative bioavailability study using a partial cross-over design. Urinary recovery (0-72 hours) was used as a measure of extent of absorption. Peak serum concentration was used as a measure of rate of absorption. The three dosage forms having the highest dissolution rate in vitro were absorbed to the same extent, while slower dissolving tablets were not as fully absorbed. Peak serum concentration correlated linearly with in vitro dissolution rate. Single oral doses of oxazepam tablets containing 10, 15 and 25 mg showed equal rates and extents of absorption and produced serum concentrations linearly correlated with dose.