What is the definition or description of: Famvir (famciclovir) allergy?

Famvir Allergy. Allergic reactions occur when your body produces antibodies to substances /allergens that are often harmless to other people. Reactions may severe or mild. Famvir (famciclovir) is an antiviral medication. Anaphylactic reactions, seizures, Stevens-Johnson syndrome, angioedema, vasculitis, toxic epidermal necrolysis, renal failure & erythema multiforme have occurred.