ABSTRACT
Drugs must be present in a solution form to traverse the biological barriers such as gastrointestinal (GI) mucosa. Thus, the process of dissolution becomes an integral part of the various rate-limiting steps leading to a clinical response. However, dissolution alone is not sufcient to provide the absorption of drugs. The drug molecules must have the characteristics required for crossing the various lipoid layers or membranes in order to reach the general circulation. Lack of sufcient aqueous solubility is usually the rate-limiting step in the dissolution process, and lack of sufcient lipophilic properties is the usual rate-limiting step in the penetration of the lipoid barriers. Attempts to rectify dissolution problems can therefore lead to problems in membrane transport, and vice versa. A ne balance between the hydrophilic and lipophilic properties is needed to provide optimum delivery of drugs to the site of action.
