Contact Photoallergy to Isothipendyl Chlorhydrate

Isothipendyl chlorhydrate is an azaphenothiazine, an active ingredient of an antipruriginous gel, Apaisyl gel® (Merck Médication Familiale, Dijon, France). Although Apaisyl gel is registered and used worldwide, we present the first case of contact photoallergy to isothipendyl chlorhydrate to our knowledge. The diagnosis suspected on the basis of a positive UVA photopatch test to chlorpromazine was confirmed by a strongly positive UVA Apaisyl gel photopatch test and our photophysical studies. This case confirms the need to keep the phenothiazines in the photopatch test standard series as a diagnostic marker of phenothiazine photoallergy.