Acyclovir
Acyclovir Prescribing Information
Acyclovir is indicated for the acute treatment of herpes zoster (shingles).
800 mg every 4 hours orally, 5 times daily for 7 to 10 days.
Acyclovir is contraindicated for patients who develop hypersensitivity to acyclovir or valacyclovir.
See
The pharmacokinetics of acyclovir after oral administration have been evaluated in healthy volunteers and in immunocompromised patients with herpes simplex or varicella-zoster virus infection. Acyclovir pharmacokinetic parameters are summarized inTable 1.
| *Bioavailability decreases with increasing dose. | |
| Parameter | Range |
| Plasma protein binding | 9% to 33% |
| Plasma elimination half-life | 2.5 to 3.3 hr |
| Average oral bioavailability | 10% to 20%* |
In one multiple-dose, crossover study in healthy subjects (n = 23), it was shown that increases in plasma acyclovir concentrations were less than dose proportional with increasing dose, as shown inTable 2. The decrease in bioavailability is a function of the dose and not the dosage form.
| Parameter | 200 mg | 400 mg | 800 mg |
| Cmax | 0.83 mcg/mL | 1.21 mcg/mL | 1.61 mcg/mL |
| Ctrough | 0.46 mcg/mL | 0.63 mcg/mL | 0.83 mcg/mL |
There was no effect of food on the absorption of acyclovir (n = 6); therefore, acyclovir tablets may be administered with or without food. The only known urinary metabolite is 9-[(carboxymethoxy)-methyl]guanine.
Acyclovir is a synthetic nucleoside analogue active against herpesviruses. Acyclovir tablets are formulations of an antiviral drug for oral administration. Each 800-mg tablet of acyclovir contains 800 mg of acyclovir and the inactive ingredients corn starch, microcrystalline cellulose, magnesium stearate, and sodium starch glycolate. Each 400-mg tablet of acyclovir contains 400 mg of acyclovir and the inactive ingredients corn starch, microcrystalline cellulose, magnesium stearate, and sodium starch glycolate. Acyclovir is a white, crystalline powder with the molecular formula C
8H
11N
5O
3 and a molecular weight of 225. 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 6H-purin-6-one, 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]; it has the following structural formula:
