Tardive dyskinesia: probing abnormal metabolism with promethazine

Ten in-patients with tardive dyskinesia (TD) (mean AIMS score 16.7) and 8 controls were recruited to the study, and 3 h after oral administration of promethazine a blood sample was taken for assay of levels of promethazine and its immediate metabolites by high-performance liquid chromatography (HPLC). The TD group had a variety of indicators of impaired or slow metabolism compared to the controls. There was a significant difference in the ratio of promethazine to promethazine sulphoxide (P<0.05) between patients with TD and the control group. The TD group but not the controls showed increasing metabolic impairment with age. This small study confirms the previous reports of impaired neuroleptic metabolism in TD, particularly in the elderly.