Salt selection for basic drugs

An attempt has been made using a Kepner-Tregoe decision analysis approach to provide rationale to salt selection for basic drugs. The selection objectives are reviewed in terms of the 'essential' (MUSTS)and 'desirable' (WANTS)issues. The desired characteristics of the salt form, given sufficient strength and toxicological suitability of the conjugate acid, are then discussed on the basis of the various pivotal physicochemical properties; melting point, aqueous solubility and dissolution rate, stability and hydrophobicity. Several trends are established which can then assist the decision of which range of salt forms to evaluate to overcome a particular problem with a basic drug. It is concluded that it is important to view the choice of salt form for development as a compromise, with particular focus on the correctly weighted desires to obtain the best balanced choice.