D1-, D2-, and 5-HT2-receptor occupancy in clozapine-treated patients.

Positron emission tomography (PET) and selective radioligands were used to determine central D1- and D2-dopamine- and 5-HT2-receptor occupancy in clozapine-treated patients with schizophrenia. In 16 patients, the mean D2-receptor occupancy was 47% (range, 20%-67%), which is lower than that previously demonstrated in patients treated with classical neuroleptics (range, 70%-89%). In 11 patients, the mean D1-receptor occupancy was 44% (range, 33%-59%), which is high when compared with that for classical neuroleptics. In a group of 5 patients, including some treated with low doses of clozapine, the mean 5-HT2-receptor occupancy was a high 89% (range, 84%-94%). By comparison to classical neuroleptics, clozapine is atypical with regard to central binding characteristics in the brain of treated patients.