ARTIFACTS IN THE ANALYSIS OF THIORIDAZINE AND OTHER NEUROLEPTICS

Although the sensitivity to light of thioridazine and its metabolites has been described, the problem does not seem to be widely acknowledge d. Indeed, a survey of the literature shows that assays of these compo unds under light-protected conditions have been performed only in a fe w of the numerous analytical studies on this drug. In the present stud y, thioridazine, its metabolites, and 18 other neuroleptics were teste d for their sensitivity to light under conditions used for their analy sis. The results show that light significantly affects the analysis of thioridazine and its metabolites. It readily causes the racemization of the isomeric pairs of thioridazine 5-sulphoxide and greatly decreas es the concentration of thioridazine. This sensitivity to light varied with the medium used (most sensitive in acidic media) and also with t he molecule (in order of decreasing sensitivity: thioridazine > mesori dazine > sulforidazine). Degradation in neutral or basic media was slo w, with the exception of mesoridazine in a neutral medium. Twelve othe r phenothiazines tested, as well as chlorprotixene, a thioxanthene dru g, were found to be sensitive to light in acidic media, whereas flupen thixol and zuclopenthixol (two thioxanthenes), clozapine, fluperlapine , and haloperidol (a butyrophenone) did not seem to be affected. In ad dition to being sensitive to light, some compounds may be readily oxid ized by peroxide-containing solvents.