An open label trial of raclopride in acute schizophrenia. Confirmation of D2-dopamine receptor occupancy by PET.

Raclopride, a highly selective D2-dopamine receptor antagonist, was administered in doses up to 4 mg b.i.d. to ten schizophrenic patients in an open label non-comparative study lasting 4 weeks. Safety, tolerability, potential antipsychotic effect, prolactin response and drug effect on plasma homovanillic acid were evaluated. Central D2-dopamine receptor occupancy was determined by positron emission tomography (PET). No major deviations were found in biochemical and physiological safety parameters. Raclopride was well tolerated. The mean BPRS score was reduced by 55% at endpoint. In the global evaluation seven patients were "very much" or "much" improved. Extrapyramidal side effects were recorded in four patients and disappeared after dose reduction or single doses of biperiden. An increase in plasma prolactin of short duration was observed in both sexes. A significant decrease of plasma HVA was obtained after 4 weeks of treatment. In two of the patients the central D2-dopamine receptors occupancy was measured using PET. The receptor occupancy was 68 and 72% which is the same as that found in patients treated with conventional neuroleptics.