Objective: Formation of clindamycin hydrochloride (clindamycin HCl) in monohydrate-ethanolate from the recrystallization process with ethanol–water (5:2) has been reported a long time ago. However, the effect of ethanol-water compositions into pseudo-polymorphism formation and its stability of was not reported yet. This study aimed to investigate the effect of ethanol-water proportion on the formation of clindamycin HCl-monohydrate and its ethanol solvate. Methods: Clindamycin HCl was recrystallized with the various percentages of ethanol. The fresh and after storage for 24 h at humidity and room temperature (25±2 °C, RH: 70±1%) crystals were characterized by FTIR (Fourier transform infra-red), PXRD (powder x-ray diffractometer), and DTA (differential scanning calorimeter). The study of desolvation/dehydration then was observed with a polarization microscopy-plate heater. Results: The results showed that monohydrate crystal was obtained from recrystallization in a concentration less than 50% ethanol in water. Next, the ethanolate was produced from the solvent of>70% ethanol. Meanwhile, the 50–70 % ethanol produced a hydrate–ethanolate, crystal, which has both hydrate and ethanol in its lattice. This hydrate-ethanolates was unstable, even in ambient temperature. Conclusion: Concentration of ethanol in water as the solvent will determine the clindamycin HCl pseudo polymorphism, which will back to its original crystal form by the time of storage.
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