Application of a primate model for tardive dyskinesia.

Persistent signs of oral dyskinesia (tongue protrusion and facial grimacing) had developed as a result of earlier chronic treatment with neuroleptics in a Cebus apella monkey. When this animal was given single doses of any classical neuroleptic, a transient deterioration of dyskinesia occurred, preceded by a temporary abolishment of dyskinesia sometimes with an attack of acute dystonia. Fluphenazine (5-25 micrograms/kg) causes dose-related deteriorations of dyskinesia. Six different drugs were tested on this monkey for their capacity to elicit aggravation of dyskinetic signs: three antihistamines (brompheniramine, promethazine, diphenhydramine) and three dopamine D2 receptor antagonists (sulpiride, tiapride, metoclopramide). High doses of promethazine and diphenhydramine (5 mg/kg) induced a temporary alleviation of dyskinesia, possibly through sedation. All three D2 receptor antagonists precipitated signs of acute dystonia at some dose levels, but out of the test drugs only metoclopramide caused deterioration of dyskinetic symptoms. According to the present results only metoclopramide stands out as a drug with an inherent propensity to cause tardive dyskinesia.