Abstract: The present invention provides a drying process for preparing crystalline solid famciclovir form I comprising the steps of: i) preparing a wet crystalline form of famciclovir; ii) drying the wet crystalline form of famciclovir at a temperature of below 50° C. until the crystalline form contains less than 15% (wt/wt) wetness; and iii) drying the wet crystalline form of famciclovir at a temperature of above 50° C. until the wet crystalline form of famciclovir contains less than 0.05% (wt/wt) water to obtain crystalline solid famciclovir form I.