Drug Dissolution Enhancement by Salt Formation: Current Prospects

Salt formation is the most common and effective method of increasing solubility and dissolution rates of acidic and basic drugs. The physicochemical principles of salt solubility and the influence of P^H solubility profiles of acidic and basic drugs on salt formation and dissolution are discussed. The solubility of salts of acidic or basic drugs depends on how easily they dissociate into their free acid or base forms and on interrelationships of several factors, such as intrinsic solubility, P^H, P^ka, solubility product and maximum solubility in different dissolution media of varying P^H. The interrelationships of these factors are elaborated and their influence on salt screening and the selection of optimal salt forms for development are explained. Salt screening is increasingly being adapted to high throughput experimentation, to shortlist the potential salt(s) for a comprehensive biopharmaceutical characterization at the scale up stage. The suitable salt form is then processed to the next stage of drug development.