Response surface analysis of solution-mediated polymorphic transformation of buspirone hydrochloride

Buspirone hydrochloride has several polymorphs including Form 1 and Form 2. The solution-mediated transformation of Form 2 to Form 1 has been studied in this research. The interconversion of two polymorphs can occur in the salt formation step which is the last step for producing this drug. In addition, the effect of co-solvent and rate of addition of acid to the solution were investigated on the extent of interconversion of Form 2 to Form 1. It has been found that pH, co-solvent ratio and amount of solvent have more influence on polymorphic interconversion. A factorial design approach was used to carry out a response surface analysis to identify the more important factors affecting the interconversion of polymorphs and find the optimum experimental conditions for the production of the desired polymorph. Quantitative characterization of the product was done by XRPD, FT-IR, SEM, DSC and TSI-PSD.