Acyclovir Side Effects: Brand Name Zovirax.  Acyclovir is available in 200 mg, 400 mg and 800 mg capsules/tablets and as a 200 mg/ 5 ml liquid.  It is also sold as an ointment used topically for oral and genital herpes treatment.  Acyclovir is a remarkably safe medication with serious side effects occurring only rarely.  It is routinely used in pregnancy and safely used in neonates with congenital herpes simplex infections.  It is used for both primary and recurrent herpes simples and herpes zoster infections.  Herpes simplex is generally more sensitive to acyclovir and higher doses are needed for herpes zoster infections.  See the manufacturer’s prescribing guidelines for dosing for specific indications.

Common Acyclovir Side Effects:  The manufacturer lists several side effects as common with acyclovir but even these are relatively uncommon and usually mild.  Listed as common acyclovir side effects are gastrointestinal side effects including diarrhea, nausea and vomiting, as well as CNS (central nervous system) side effects including headache, dizziness, malaise, lethargy, and confusion.  Other common acyclovir side effects include arthralgia and skin rashes or photosensitivity. When used by injection a reaction at the site of injection is common.

Serious Acyclovir Side Effects: Serious acyclovir side effects are very unusual and include seizures, coma, blood dyscrasias like leukopenia and thrombocytopenia, and renal impairment.

Drug Interactions and Cautions: Acyclovir use with cidofovir and streptozocin is contraindicated. Use with aminoglycosides, several HIV drugs and drug combinations and a few other uncommonly used medications require use of alternative drugs if possible. Careful monitoring for interaction effects is needed with a longer list of medications including cimetidine, Acyclovir metabolism is both renal and through the CYP450 hepatic metabolism pathway.

Acyclovir use in Pregnancy and Lactation: Pregnancy category B and felt to be safe in breast feeding women. Acyclovir is safely, and often, used in late pregnancy to prevent recurrent genital herpes simplex outbreaks that could lead to vertical transmission from mother to infant with vaginal childbirth.

Unusual Side Effects: Acyclovir is really unusual in that so few patients using it actually experience side effects. One issue experienced by patients who have used acyclovir  is with use for prevention of genital herpes outbreaks after discontinuation of the drug. Some patients experience more frequent episodes of herpes recurrences for awhile after stopping the drug. For use at the onset of a recurrent herpes outbreak, the earlier a person starts the medication the more benefit they have in shortening the duration and severity of the outbreak. Although acyclovir is used to reduce the frequency of herpes outbreaks, or to shorten the duration of outbreaks when used intermittently acyclovir use does not assure that a sexual partner will not acquire a herpes simplex infection from the infected person taking the acyclovir.

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