An open-label study evaluated the safety (n = 53) and pharmacokinetics (n = 8) of single-dose therapy with 1500 mg famciclovir (prodrug of penciclovir) for recurrent herpes labialis in adolescents. Mean Cmax, mean AUC0-∞, and clearance for penciclovir were 9.37 μg/mL, 31.8 μg · h/mL, and 38.2 L/h, respectively, and within the range extrapolated from data in adults. Adverse events were generally mild and transient.