ABSTRACT
Adequate oral bioavailability is a key pre-requisite for any orally administered drug to be systemically effective. Dissolution (release of the drug from the dosage form) is of primary importance for all conventionally constructed, solid oral dosage forms in general, and for modified-release dosage forms in particular, and can be the rate limiting step for the absorption of drugs administered orally (1). Physicochemically, ‘‘Dissolution is the process by which a solid substance enters the solvent phase to yield a solution’’ (2). Dissolution of the drug substance is a multi-step process involving
heterogeneous reactions/interactions between the phases of the solute-solute and solvent-solvent phases and at the solute-solvent interface (3). The heterogeneous reactions that constitute the overall mass transfer process may be categorized as (i) removal of the solute from the solid phase, (ii) accomodation of the solute in the liquid phase, and (iii) diffusive and/or convective transport of the solute away from the solid/liquid interface into the bulk phase. From the dosage form perspective, dissolution of the active pharmaceutical ingredient, rather than disintegration of the dosage form, is often the rate determining step in presenting the drug in solution to the absorbing membrane. Tests to characterize the dissolution behavior of the dosage form, which per se also take disintegration characteristics into consideration, are usually conducted using methods and apparatus that have been standardized virtually worldwide over the past decade or so, as part of the ongoing effort to harmonize pharmaceutical manufacturing and quality control on a global basis.
