Born out of Fire and Ice: Polymorph Studies of the Antiviral Famciclovir

There is much interest and focus on solid forms of famciclovir. However, in spite of the abundance of reported differences in oral bioavailability, compressibility, and other physical-chemical properties of the various crystal forms of this drug, very little precise structural analysis is available in the literature to date. The form used in the commercial formulation is the anhydrous form I. Patents and patent applications report three different anhydrous crystalline forms on the basis of unindexed powder diffraction patterns. Single-crystal and variable-temperature X-ray diffraction experiments using the commercially available anhydrous form of famciclovir were carried out and led not only to the crystal structure determination of the anhydrous form I, but also to discovery of a new crystal form of anhydrous famciclovir from powder data.

Automated summary

Despite the abundance of reported differences in the physical-chemical properties of various crystal forms of famciclovir, there is still little precise structural analysis available in the literature. The anhydrous form I is used in commercial formulations. Research using commercially available anhydrous famciclovir led to the determination of the crystal structure of form I and the discovery of a new crystal form.