The in vitro bioavailability of various drugs formulated as hard gelatin capsules.

A factorially designed experiment has been carried out to study the influence of various additives on the in vitro release of drug from hard gelatin capsules. Analysis of variance confirms previous findings that, although the main factors of diluent type, diluent concentration, the absence and presence of both magnesium stearate and sodium lauryl sulphate, were highly significant, the existence of interactions between the factors prevented exact quantitative prediction of the influence of each factor. There appears however, to be a strong indication that the in vitro drug release of capsule formulations (y), expressed as the % of the drug content of the capsule which dissolves, can be related to the solubility of the drug (cs) by the expression y = 21-2 log cs + 31.2.