Dissociation constants, solubilities and dissolution rates of some selected nonsteroidal antiinflammatories

Abstract

Dissociation constants, solubilities and dissolution rates have been investigated for 16 nonsteroidal antiinflammatory active compounds which belong to several chemical groups within the small class of acidic drug substances. The antiinflammatories are mostly characterized by a very low aqueous solubility at lower pH-values. The solubilities increase rapidly with pH's higher than the pK_a. The pK_a-values of the investigated compounds range from 3.5 to 6.3 with a mean directed to 4.6. The dissolution rate determinations of equimolar amounts at pH 7.5 show a great variation from half a minute to 60 minutes for the 50% level.