ABSTRACT
Drugs must be present in a solution form to cross biologic barriers such as the gastrointestinal
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 sufficient 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 sufficient aqueous solubility is usually the rate-limiting step in the dissolution
process, and lack of sufficient 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 fine balance between the
hydrophilic and lipophilic properties is needed to provide optimum delivery of drugs to
the site of action.
