The main drug ingredient of famciclovir granules is famciclovir. Famciclovir is a broad-spectrum antiviral drug with strong inhibitory effect mainly on herpes simplex virus type 1 and 2, and also on other viruses such as varicella-zoster virus and EBV, which is given orally and has a good therapeutic effect. It is mainly used clinically for the treatment of herpes zoster and primary genital herpes. Adverse reactions to famciclovir are relatively rare, with gastrointestinal reactions being the most common, including nausea, vomiting, abdominal discomfort, diarrhea, occasional fever, headache, general malaise, hypotension and rash, most of which disappear quickly after discontinuation of the drug.