Effect of Common Excipients on the Oral Drug Absorption of Biopharmaceutics Classification System Class 3 Drugs Cimetidine and Acyclovir

The objective was to assess the impact of larger than conventional amounts of 14 commonly used excipients on Biopharmaceutics Classification System (BCS) class 3 drug absorption in humans. Cimetidine and acyclovir were used as model class 3 drugs across three separate four-way crossover bioequivalence (BE) studies (n = 24 each) in healthy human volunteers, denoted as study 1A, 1B, and 2. In study 1A and 1B, three capsule formulations of each drug were manufactured, collectively involving 14 common excipients. Capsule formulations that incorporated hydroxypropyl methylcellulose (HPMC) or magnesium stearate exhibited lower absorption. The cimetidine commercial solution contained sorbitol and also resulted in lower absorption. Hence, in study 2, two capsule formulations with lower amounts of HPMC and magnesium stearate, the sorbitol-containing commercial solution, and a sorbitol-free solution were assessed for BE. Overall, 12 common excipients were found in large amounts to not impact BCS class 3 drug absorption in humans, such that these excipients need not be qualitatively the same nor quantitatively very similar to reference, but rather simply be not more than the quantities studied here. Meanwhile, for each HPMC and microcrystalline cellulose, BCS class 3 biowaivers require these two excipients to be qualitatively the same and quantitatively very similar to the reference.