Phenothiazine phototoxicity: an experimental study on chlorpromazine and related tricyclic drugs

A large number of phenothiazines and chemically related tricyclic drugs have been studied with respect to their phototoxic potency. Two methods were used, an in vivo technique based on the inflammatory response of the mouse tail after systemic administration of the drug plus UVA irradiation, and an in vitro method based on growth inhibition of Candida albicans. Of 27 commercial tricyclic drugs tested in vivo, the most potent were chlorpromazine and two other chlorinated compounds, prochlorperazine and perphenazine. Tricyclic drugs lacking nitrogen, sulphur, or both in their ring system showed no activity. All compounds phototoxic in the mouse were so in the yeast test as well. Here, however, the thioxanthenes (lacking nitrogen) were also highly active.