Salt Selection
Salts of active pharmaceutical ingredients (APIs) are often used when the API itself is not sufficiently soluble or stable, or is difficult to formulate or manufacture. In addition, different salt forms can have different bioavailability profiles or organoleptic properties.
Current thinking is that salts represent one end of a structural continuum, with cocrystals at the opposite end (see Childs, S. L.; Stahly, G. P.; Park, A. Molecular Pharmaceutics 2007, 4, 323-338 for a discussion).
When considering making salts of an API, one needs to select appropriate counter ions (or cocrystal guests) based on a variety of factors such as frequency of use in approved drugs, dissociation constants, expected salt solubilities, and so forth.
Chemfocus can plan an efficient salt selection project considering those factors and the particular properties and intended use of an API. See the Solid Form Screening and Selection section for a brief discussion of cocrystals.