Metronidazole in the Treatment of Rosacea

To the Editor.— In the July issue, the hypothesis of Drs Kurkcuoglu and Atakan 1 that metronidazole's effects on rosacea may be due to the agent's antiparasitic activity against the mite Demodex folliculorum is an interesting one. While studying the survival of D folliculorum in solutions of metronidazole, we found that the mites can survive even in concentrations of as much as 1 mg/mL. 2 Such levels are unlikely to occur in the skin, in view of the fact that after oral administration of 500 mg of metronidazole, the blood level reaches 15 μg/mL. 3 It is to be noted, however, that metronidazole is degraded into at least five metabolites with potential biologic activity, 4 among which the major urinary product, the 2-hydroxymethyl derivative, is approximately one third to ten times more active as an antibacterial agent than is metronidazole. 5 It may be that one or more of these