Polymorphic transformation among the Form I, Form II and amorphous of clopidogrel hydrogen sulfate was carried out experimentally. In this study, the effect of solution composition, temperature and supersaturation was investigated. Supersaturation < 2.3 is acceptable for stable form, Form II formation. Supersaturation > 8.9 is required for unstable form, amorphous form. Higher supersaturation can be obtained by evaporation coupled with higher vacuum. It is concluded that the screening of polymorphs can be done by control of supersaturation level.
