A woman came to see me with a fever blister on the vermilion border of the lip. Six months earlier, she had treated a herpes infection with acyclovir (Zovirax), but it had no effect on the fever blister. What treatment do you recommend? — Chinwe V. Nduka, MPS, PA-C, New York City

It may be appropriate to first determine or confirm the diagnosis of the lip blister. Herpes simplex virus (HSV) infection can be established by performing a viral culture with virus subtyping from the blister base and fluid. Alternatively, a Tzanck smear preparation from the blister base can be evaluated for the presence of multinucleated epithelial giant cells.

Recurrent herpes labialis can be treated with acyclovir (200 mg every four hours, five times daily, for five days), valacyclovir (Valtrex) (500 mg b.i.d. for three to five days or 2 g every 12 hours for one day [two doses total]), or famciclovir (Famvir) (125 mg b.i.d. for five days). Failure of the blister to respond to antiviral therapy may indicate an alternative diagnosis for the lesion or an acyclovir-resistant strain of HSV. — Philip R. Cohen, MD (173-3)

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