Amorphous solid dispersion: a promising technique for improving oral bioavailability of poorly water-soluble drugs

Abstract

Out of many, one of the most promising strategies to improve the oral bioavailability of poorly water-soluble drugs is to develop amorphous solid dispersions. Reduction in drug particle size improves drug wettability and oral bioavailability significantly. Poorly soluble drugs are benefited by formulation approaches that overcome the issue of poor solubility and dissolution rate limited bioavailability. As Gibbs free energy is higher, the solubility of amorphous compounds is much greater than the more stable crystalline form. Moreover, amorphous forms are kinetically trapped high energy disordered materials that lack the periodicity of crystals but behave mechanically as solids. Lipophilic drugs, especially those belonging to the biopharmaceutics classification system (BCS) class II and IV, dissolve at a slower rate, leading to incomplete release of drug from the dosage form, poor oral bioavailability, increased food effect, and high inter-patient variability. Hence, to improve the solubility and dissolution of poorly water-soluble drugs, several formulation approaches can be considered, among which formulating the active pharmaceutical ingredient (API) in an amorphous form is recently gaining prominence. Formulating amorphous solid dispersions of poorly water-soluble drugs with water-soluble carriers has reduced the incidence of these problems and enhanced the rate of dissolution. This review mainly focuses on advantages, classification of solid dispersion, methods of preparation, and characterisation of the amorphous solid dispersion.