Interactions between procyclidine and neuroleptic drugs. Some pharmacological and clinical aspects

Procyclidine was administered to 25 chronic psychotic inpatients, stabilised on chlorpromazine, haloperidol or fluphenazine decanoate injection. We observed a significant reduction in mean serum levels of all three neuroleptic drugs which was reversed on stopping procyclidine and was inversely correlated with mean serum procyclidine levels. No significant alterations occurred on the BPRS scores or in serum prolactin levels throughout the study in any of the three groups. Possible mechanisms of this interaction and its clinical relevance are discussed.