Physical characterization of pentamidine isethionate during freeze-drying-relevance to development of stable lyophilized product

Prakash Sundaramurthi, Michael R. Burcusa, Raj Suryanarayanan

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The purpose of this study was to perform physical characterization of pentamidine isethionate (PI) in frozen and freeze-dried systems and to monitor the phase behavior during all the stages of freeze-drying. Frozen aqueous PI solutions as well as the final lyophiles were characterized by differential scanning calorimetry and X-ray diffractometry. The effect of cosolutes, cosolvents, and processing conditions on the PI crystallization behavior during freeze-drying was evaluated. In frozen aqueous solutions, irrespective of the cooling rate and the initial solute concentration, PI readily crystallized as a trihydrate (C19H24N4O2·3H2O). It dehydrated to a poorly crystalline anhydrate upon drying at 100mTorr. The presence of a readily crystallizing cosolute or an organic cosolvent did not influence the physical form of PI in the final lyophile. On the contrary, even in the absence of cosolutes and cosolvents, the crystalline trihydrate was retained when the chamber pressure was increased to 500mTorr. By altering the drying conditions, it was possible to obtain either a crystalline trihydrate or a poorly crystalline anhydrate. The stability of PI is dependent on its physical form and only the amorphous PI undergoes discoloration. The PI stability can be enhanced by retaining it in a crystalline state in the lyophile.

Original languageEnglish (US)
Pages (from-to)1732-1743
Number of pages12
JournalJournal of Pharmaceutical Sciences
Issue number5
StatePublished - May 2012

Bibliographical note

Funding Information:
Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.


  • Amorphous
  • Crystallization
  • Dehydration
  • Differential scanning calorimetry
  • Formulation
  • Freeze-drying
  • Pentamidine isethionate
  • Physical characterization
  • Physical stability
  • Polymorphism
  • X-ray diffractometry


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