RELATION OF SERUM ANTICHOLINERGICITY TO COGNITIVE STATUS IN SCHIZOPHRENIA-PATIENTS TAKING CLOZAPINE OR RISPERIDONE

Background: A potential beneficial outcome of treatment with certain o f the atypical neuroleptics is the reduced risk of cognitive impairmen t, stemming from purported low affinity for cholinergic receptors. In vitro experiments have shown that clozapine is highly anticholinergic and risperidone is minimally so. In vivo tests of the anticholinergic burden imposed by these medications and its potential cognitive conseq uences are needed. This study examines anticholinergic burden in schiz ophrenia patients taking clozapine and risperidone and tests whether t his burden is associated with cognitive deficits. Method: Serum antich olinergic levels were determined in a sample of 22 chronic schizophren ia patients using the radioreceptor assay method of Tune and Coyle (19 80). Fifteen patients received clozapine; 7 received risperidone. Mean +/- SD age of the sample, comprising 12 men and 10 women (68% white), was 44.7 +/- 8.4 years. Mean +/- SD age at onset of schizophrenia ill ness was 23.5 +/- 7.4 years. Two anticholinergic assays based on blood samples collected 1 week apart were available on each patient. Result s: Data indicated that clozapine patients had significantly (p <.001) higher anticholinergic levels at both collection points, and levels fo r both drugs remained stable over time. The clozapine and risperidone patients had essentially equivalent scores on the cognitive measure. C onclusion: These data suggest that anticholinergicity distinguishes cl ozapine and risperidone in vivo but that this effect is not associated with differences in global cognitive functioning. Results suggest tha t clozapine, despite producing moderately high in vivo serum anticholi nergic levels, still holds clinical advantage over standard neurolepti cs in terms of cognitive side effects. Reasons for this lowered risk o f cognitive impairment are discussed.