Famvir contains famciclovir, an orally administered prodrug of
the antiviral agent penciclovir. Chemically, famciclovir is known as 2-[2-(2-amino-9H-purin-9-yl)ethyl]-1,3-propanediol
diacetate. Its molecular formula is C14H19N55O4
; its molecular weight is 321.3. It is a synthetic acyclic guanine derivative.
Famciclovir is a white to pale yellow solid. It is freely soluble in
acetone and methanol, and sparingly soluble in ethanol and isopropanol.
At 25C famciclovir is freely soluble (>25% w/v) in water initially, but
rapidly precipitates as the sparingly soluble (2-3% w/v) monohydrate.
Famciclovir is not hygroscopic below 85% relative humidity. Partition
coefficients are: octanol/water (pH 4.8) P=1.09 and octanol/phosphate
buffer (pH 7.4) P=2.08.
Tablets for Oral Administration: Each white, film-coated tablet
contains famciclovir. The 125 mg and 250 mg tablets are round; the 500
mg tablets are oval. Inactive ingredients consist of hydroxypropyl cellulose,
hydroxypropyl methylcellulose, lactose, magnesium stearate, polyethylene
glycols, sodium starch glycolate and titanium dioxide.