Modified-Release Drug Delivery Systems: Bioavailability

Modified-release or MR dosage forms are designed to prolong drug release and maintain steady plasma drug levels, minimizing fluctuations compared to conventional-release formulations and improving therapeutic outcomes.

Their bioavailability is typically under 100% due to incomplete drug release, prolonged absorption phases, and first-pass metabolism in orally administered drugs.

So, studying the in vivo bioavailability of MR formulations is crucial. These studies measure the fraction of drug absorbed, potential dose dumping, and the effects of food and circadian rhythms on drug absorption. Single-dose studies evaluate absorption, while multiple-dose studies assess sustained therapeutic levels, steady-state concentration ratios, and percent fluctuation.

Immediate-release formulations, and in some cases oral solutions or suspensions, serve as reference standards for comparison when evaluating MR products.

Additionally, in vitro bioequivalence tests simulate in vivo conditions to assess drug release profiles. This uses biorelevant dissolution media, considering variations in gastrointestinal pH, fed versus fasted states, and the presence of digestive secretions.