Introduction to Biopharmaceutics Measures

This chapter explains why solubility, permeability, and dissolution are important in biopharmaceutics assessment. A drug needs to be in solution to undergo pharmacological processes in vitro and in vivo. There are many strategies that formulation scientists can apply to improve the solubility of a drug; there are also aspects that medicinal chemists can adapt to provide optimised drug candidates. Whilst solubility assessment is typically focussed on the drug substance; dissolution is a parameter more relevant for a formulated drug product. Membrane permeability is needed for drug distribution and elimination following absorption. Permeability of the drug across the relevant membrane is a key measurement within biopharmaceutics. Using the simple biopharmaceutics measures the permeability and likely concentration gradient (identified via the solubility) can be predicted thus the absorptive flux estimated.