Solid-State Properties of Tobramycin

Alekha K. Dash, Raj Suryanarayanan

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25 Scopus citations


Tobramycin I obtained from two different sources was subjected to powder X-ray diffractometry, thermal analyses, and Karl Fischer titrimetry. It was concluded to be tobramycin monohydrate (C18H37N5O9 · H2O). When heated in the differential scanning calorimeter (DSC), the dehydration of I resulted in the formation of metastable anhydrous tobramycin, which melted at 164°C. This was followed by the crystallization of the stable anhydrous tobramycin, which then melted at 217°C. The polymorphic transition was concluded to be monotropic and the calculated free energy difference between the metastable and the stable forms, at 25°C, was 348 cal · mol−1. Both the heating rate in the DSC and the sample size had a significant influence on the enthalpy values of most of the thermal events. These observations were attributed to the presence of trace amounts of moisture in the sample. No detectable decomposition of I occurred when it was heated up to 224°C.

Original languageEnglish (US)
Pages (from-to)1159-1165
Number of pages7
JournalPharmaceutical Research: An Official Journal of the American Association of Pharmaceutical Scientists
Issue number9
StatePublished - Sep 1991

All Science Journal Classification (ASJC) codes

  • Biotechnology
  • Molecular Medicine
  • Pharmacology
  • Pharmaceutical Science
  • Organic Chemistry
  • Pharmacology (medical)


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