Pharmacological characterization of tardive dyskinesia.

Tardive dyskinesia (TD) may be a clinical manifestation of a relative imbalance between the inversely related dopaminergic (DA) and acetylcholinergic (ACh) influences in the central nervous system (CNS). Six patients were evaluated with single challenge doses of a DA agonist, levodopa, and antagonist, droperidol, as well as with an ACh agonist, physostigmine, an antagonist, benztropine, and a placebo. A single blind trial with deanol and placebo followed. Responses, measured by an electrophysiological technique, formed two subgroups. The patients who improved with a DA antagonist or an ACh agonist improved while taking deanol. Another group of patients were made worse with a DA antagonist or ACh agonist and were worsened or had no response while taking deanol. While the results add support to the concept of counterbalancing DA-ACh influences in TD, further investigation of TD subtypes and predictors of drug response is warranted.