Anticholinergic equivalents and parkinsonism: a model for predicting side-effects of antipsychotic drugs

The tendency of antipsychotics to produce extrapyramidal side-effects varies inversely with their antimuscarinic activity. This paper reviews the antipsychotic and antimuscarinic potency of these drugs and compares the total antimuscarinic activity in standard daily doses of antipsychotics, antiparkinson agents and antidepressants. The authors examine factors associated with tolerance of benztropine withdrawal in 39 inpatients. Patients with serious EPS relapse after benztropine withdrawal had an excess of antipsychotic over antimuscarinic activity in their remaining medications. The results suggest an optimal ratio between total antipsychotic and anticholinergic doses, and a simple model for predicting antiparkinson drug requirements.