Failure of Neutral-Red Photodynamic Inactivation in Recurrent Herpes Simplex Virus Infections

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Abstract
Because photodynamic inactivation of herpes simplex virus infections may not be free of hazard, the efficacy of photodynamic inactivation with neutral red and light was evaluated in a placebo-controlled study of 170 episodes of recurrent herpes simplex virus infection in 96 patients. The preparation of neutral red that was used was shown to photoinactivate herpes simplex virus in vitro, but had no significant effect on the rate of resolution of herpetic lesions (P>0.10) or on the frequency of subsequent recurrences (P>0.10), except for orolabial lesions, in which an adverse effect on the rate of subsequent recurrences was observed (P<0.05). In the absence of demonstrated efficacy, the routine use of neutral red and light in patients with recurrent herpes simplex virus infections should be discontinued. Furthermore, other photoactive dyes should not be used until their efficacy has been demonstrated by suitably controlled clinical trials. (N Engl J Med 293:945–949, 1975)