Minimizing bioavailability variations with oral controlled release formulations

Despite various routes of drug delivery being explored, the oral route has continued to be the most popular route of drug administration. However, the complexities associated with the gastrointestinal tract lead to variations in the rate and extent of bioavailability of drugs administered as oral dosage forms. This variation in the bioavailability of drugs is responsible for the majority of adverse effects, lack of efficacy, and development of tolerance, etc. This review explores the possibilities of minimizing these bioavailability variations with the use of oral controlled release (CR) dosage forms. The use of CR preparations, in lieu of the immediate preparations in itself, leads to better control over plasma levels. Furthermore, the additional benefits offered by CR products, such as the reduction in first-pass metabolism, enhanced and reproducible bioavailability with gastro retentive preparations, overcoming circadian rhythm variations, and the lesser effect of fed condition on bioavailability, can be effectively utilized for bioavailability variation minimization. However, CR products cannot be use indiscriminately. The use of CR products to serve the purpose of bioavailability variation minimization should be based on due consideration to the role of metabolizing enzymes, the permeability variations, and the area available for absorption.