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

• Main Authors: Liana Vella-Zarb, Ulrich Baisch
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Crystals
• Subjects: n/a
• Online Access: https://www.mdpi.com/2073-4352/11/2/129

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.