Acyclovir is a synthetic nucleoside analogue active against herpes viruses. Acyclovir capsule is a formulation for oral administration. Each capsule of acyclovir contains 200 mg of acyclovir and the inactive ingredients colloidal silicon dioxide, croscarmellose sodium, magnesium stearate and microcrystalline cellulose. The capsule shell consists of FD&C blue #1, gelatin and titanium dioxide. The capsule black imprinting ink contains the following inactive ingredients: ammonium hydroxide, black iron oxide, n-butyl, ethyl alcohol, isopropyl alcohol, potassium hydroxide, propylene glycol and shellac.

Acyclovir is a white, crystalline powder with the molecular formula C 8H 11N 5O 3 and a molecular weight of 225.2. The maximum solubility in water at 37°C is 2.5 mg/mL. The pka's of acyclovir are 2.27 and 9.25.

The chemical name of acyclovir is 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]-6 H-purin-6-one; it has the following structural formula: