Photocontact allergic and phototoxic studies of chlorproethazine

Neuriplege cream was available as a non-prescription medication in France until its withdrawal from the market by regulatory authorities in January 2007. Its active ingredient is the phenothiazine chlorproethazine (CPE). Before its withdrawal, we investigated the photocontact allergic and phototoxic potential of Neuriplege cream and CPE.

An in vitro phototoxic study was performed in HaCaT keratinocytes using the neutral red dye phototoxic assay. Phototoxicity and photocontact allergy were assessed in humans by photopatch testing.

In vitro, a 1 h incubation of keratinocytes with CPE was approximately 13 times as toxic to the cells in the presence of ultraviolet light compared with incubation with the drug alone. Of two healthy volunteers initially photopatch tested to Neuriplege cream on the arm, one developed a phototoxic reaction. These two volunteers were then photopatch tested to Neuriplege and CPE on the back with seven additional healthy volunteers. Both of the initial study volunteers experienced a photocontact allergic reaction to Neuriplege as is upon this re-exposure. Of the seven volunteers not previously exposed to Neuriplege as is, five developed phototoxic reactions.

This study demonstrates the strong phototoxic and photocontact allergic potential of CPE in Neuriplege cream, and supports the decision of the French pharmaceutical regulatory authorities to withdraw it.