The form in which a compound crystallizes can affect its physical properties. This is very relevant in the pharmaceutical industry where different crystal forms, polymorphs, can display markedly different stabilities, solubility, and/or bioavailability.

Jerry Atwood and co-workers, University of Missouri, USA, have found that the antibiotic clarithromycin (6-O-methylerythromycin A) can be transformed from forms 0 or I into form II under mild conditions. They use carbon dioxide at 100–350 psi and room temperature to convert the crystal form. The transformations are kinetically influenced as greater pressure effecting faster transformations.

Currently, form II of clarithromycin is obtained by desolvating form 0 to yield form I followed by heating for 18 h at 110 °C to enable conversion to form II. An alternative, mild route to specific polymorphs could have a large impact on the pharmaceutical industry.

• A New Strategy of Transforming Pharmaceutical Crystal Forms
  J. Tian, S. J. Dalgarno, J. L. Atwood,
  J. Am. Chem. Soc. 2011.
  DOI: 10.1021/ja107617m