Differential Effect of Haloperidol and Clozapine on Plasma Homovanillic Acid in Elderly Schizophrenic Patients with or without Tardive Dyskinesia

Background:Plasma homovanillic acid (HVA) changes in response to a challenge of several days with haloperidol have been found to be predictive of the therapeutic response to haloperidol over a longer period of treatment. Methods:Twenty-six elderly women who gave informed consent were divided into two groups, with or without tardive dyskinesia, and subjected to an 80-day washout, after which both the dyskinetic and nondyskinetic group was divided, and half of each group given haloperidol or clozapine. Conclusions:The nondyskinetic group had a brief rise in plasma HVA, then a decline. The dyskinetic group had no change in plasma HVA. Neither group challenged with clozapine had any change in plasma HVA.