Gastroretentive Formulations for Improving Oral Bioavailability of Drugs-Focus on Microspheres and their Production

Oral administration is the most commonly used drug delivery route for the majority of conditions. Given its advantages over other routes, such as convenience and cost, its use is increasing every year despite the major advances in drug delivery. Nevertheless, oral formulations are limited and challenged by physicochemical barriers and highly variable residence times. Gastric retention is a strategy that can overcome the highly variable gastric residence time by designing formulations that remain in the stomach longer than would otherwise be expected. This is especially beneficial for drugs that have an absorption window in the stomach and proximal intestine. Various techniques are discussed and include gasgenerating tablets, floating microspheres, hydrodynamically balanced systems, bioadhesive particles, rafts and modified shape systems. Microspheres having the advantages of being multi-unit are further discussed with regard to their production methods and characterisation. Further, a summary of microsphere studies is presented that looks at methods used and key results.