Zovirax (acyclovir)

In patients with impaired renal function, doses and/or frequency of administration of acyclovir must be modified in response to the degree of impairment. Generally, the decrease in total body clearance of acyclovir is directly related to the decrease in body-surface-area-corrected creatinine clearance; however, clearance of acyclovir is usually greater than predicted from creatinine clearance, since the drug undergoes some renal tubular secretion.

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No dosing information is available for this tab.

No dosing information is available for this tab.

There is no enhanced messaging for this drug.

There are no contraindication interactions for this drug.

There are no severe interactions for this drug.

There are no moderate interactions for this drug.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

There are no severe contraindications for this drug.

There are no moderate contraindications for this drug.

There is no enhanced messaging for this drug.

There are no severe adverse reactions for this drug.

There are no less severe adverse reactions for this drug.

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No enhanced messaging available.

There are no adequate and controlled studies to date using acyclovir in pregnant women, and the drug should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.

Acyclovir administered during organogenesis was not teratogenic in the mouse (450 mg/kg daily orally), rabbit (50 mg/kg daily subcutaneously or IV), or rat (50 mg/kg daily subcutaneously). These dosages resulted in plasma concentrations that were 106, 11, and 22 times, respectively, the steady-state plasma concentrations observed in humans receiving 200 or 800 mg of acyclovir orally 5 times daily. However, in nonstandard tests in rats, fetal abnormalities (e.g., head and tail anomalies) and maternal toxicity were observed with subcutaneous acyclovir. Acyclovir crosses the placenta in humans and the clinical relevance of these animal findings currently is not known.

IV acyclovir has been used during the second or third trimester of pregnancy without apparent adverse effects to the fetus. The US Centers for Disease Control and Prevention (CDC) state that first clinical episodes of genital herpes occurring during pregnancy may be treated with oral acyclovir and that use of IV acyclovir therapy may be indicated for the treatment of severe maternal HSV infections. Preliminary data suggest that acyclovir treatment late in pregnancy might reduce the frequency of cesarean sections among women who have recurrent genital herpes by diminishing the frequency of recurrences at term. The risk for HSV is high in infants born to women who acquired genital herpes in late pregnancy, and such women should be managed in consultation with an HSV specialist. Some experts recommend acyclovir therapy in this circumstance, some recommend routine cesarean section to reduce the risk for neonatal HSV, and others recommend both. (See Pregnant Women under Uses: Genital Herpes.)

Many clinicians do not recommend use of oral acyclovir in pregnant adolescents or women with uncomplicated varicella because the risk or benefit to the fetus currently is not known. However, other clinicians recommend use of oral acyclovir for the treatment of varicella in pregnant women, especially during the second and third trimesters. In addition, use of IV acyclovir is recommended in pregnant women with serious complications of varicella such as extensive cutaneous disease, high fever, or systemic symptoms. It is not known whether acyclovir administered to the mother prevents congenital varicella syndrome (i.e., low birthweight, hypotrophic limbs, ocular abnormalities, brain damage, mental retardation) in the neonate.

To monitor fetal outcomes of pregnant women exposed either inadvertently or intentionally to systemic acyclovir, the manufacturer established a prospective registry of acyclovir use during pregnancy and collected data from 1984 to April 1999. A total of 749 pregnancies were followed over this time period involving 756 outcomes, and comparison of registry data with birth defect surveillance data revealed no evidence of an increased risk for birth defects in infants of mothers treated with acyclovir during the first trimester of pregnancy. However, the sample size of the registry is insufficient to evaluate the risk for less common defects or to permit reliable or definitive conclusions regarding the safety of acyclovir in pregnant women and their developing fetuses.

Limited data indicate that acyclovir is distributed into milk, generally in concentrations greater than concurrent maternal plasma concentrations, and can be absorbed by nursing infants. Acyclovir should be administered to nursing women with caution and only when indicated.

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