Peter S. Bernstein, MD, MPH, FACOG; Peter Van Eerden, MD


June 10, 2003


How safe is acyclovir in first trimester of pregnancy, and is it safe to treat herpes zoster in the first trimester with acyclovir?

Response from Peter S. Bernstein, MD, MPH, FACOG and Peter Van Eerden, MD

Varicella zoster virus is a member of the herpesvirus family. Varicella, also known as chickenpox, is the acute primary disease. The virus incubates for 15 days and is communicable 2 days before and 5 days after the onset of the rash.[1] Herpes zoster is the recurrent form of the infection. After an initial episode with varicella zoster, leading to chickenpox, the virus may persist in a latent state in the posterior root ganglia of the spinal cord for years. Reactivation results in herpes zoster.

Varicella is a common, highly contagious, self-limited disease of childhood that is transmitted by respiratory droplets or close contact. It is usually acquired by 90% of persons in the United States before the reproductive age. Thus most women are immune before they become pregnant.[2] The incidence of varicella in pregnancy is 0.7/1000. Should varicella pneumonia develop during pregnancy, however, it can run a more fulminant course. Maternal varicella infection in the first 20 weeks of pregnancy can cause varicella embryopathy, also called congenital varicella syndrome, in approximately 1%-2% of cases.[2] This syndrome consists of the hallmark cicatricial skin lesions that present in a dermatomal distribution, limb hypoplasia, and contractures and can also involve the eye and central nervous system. The prognosis is poor should an infant be infected.[3]

Herpes zoster in pregnancy is much less common than varicella, occurring in 1/10,000 pregnancies, or 0.1%.[1] The risk of the congenital varicella syndrome is negligible, because antibodies in the maternal blood prevent the virus from crossing the placenta and infecting the fetus. In 1994, Enders and colleagues showed no clinical evidence of infection in infants born to 366 women with herpes zoster in pregnancy.[4]

Acyclovir is a class C antiviral agent used to treat herpes zoster. Oral acyclovir has been shown to significantly reduce herpes-related symptoms as well as the duration, intensity, and prevalence of zoster-associated pain.[5] The newer agents, valacyclovir and famciclovir, have a better oral bioavailability and less frequent dosing than acyclovir with similar efficacy. Oral antivirals are most beneficial in elderly or immunocompromised patients with uncomplicated herpes zoster in reducing the duration and intensity of pain.

Many studies have demonstrated the safety of acyclovir use in pregnancy. Neither medically indicated nor inadvertent use showed any adverse effect on the fetus. In 1993, the Centers for Disease Control published data showing no increased risk of fetal abnormalities in patients exposed in the first trimester.[6] Thus it seems that acyclovir is safe to use in pregnancy if indicated.


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