An observation of polymorphism in pentamidine isethionate

Two forms of pentamidine isethionate have been identified from two commercial samples of the compound. The lower melting form was produced by freeze drying and has a melting point of 133.4 degrees C whilst the higher melting form has a melting point of 192 degrees C. Powder x-ray diffraction studies showed that each modification was crystalline and the infra-red spectra showed differences that could be attributed to polymorphism. It was noted that when the freeze dried material was exposed to the atmosphere it converted to the higher melting form and was hygroscopic. Examination of this compound in a formal polymorphism screen was advocated.