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Pimozide (PMZ), a relatively specific dopamine (DA) receptor blocking drug, was compared to chlorpromazine (CPZ) in a double-blind, between-patient clinical trial in mania. The trial lasted 14 days. Twenty-three patients who fulfilled Feighner's criteria for mania entered the trial (one patient entering on two separate occasions). Both drugs led to clinical improvement, with a significant effect being noted within 24 hours. According to one of the two rating scales used, initial improvement was greater with chlorpromazine, probably due to its greater sedative effect. By 7 days both drugs were equally effective. Sedative side effects were more frequent in patients on CPZ; extrapyramidal side effects were more frequent with PMZ. The finding that the relatively specific DA receptor blocking drug PMZ was as effective as CPZ in the treatment of mania is consistent with the view that hyperactivity of central DA pathways is involved in the pathogenesis of this condition.

Pimozide and haloperidol were found to be equally effective in the treatment of acute schizophrenia in a double-blind clinical trial involving 22 patients. Drug plasma levels measured by radioimmunoassay (RIA) did not correlate with clinical response following either drug. Nor was there any correlation between clinical response and the dopamine receptor blocking activity of either drug as measured by radio receptor assay (RRA). Following pimozide plasma prolactin (PRL) levels correlated with clinical change, although the time courses of response of PRL and clinical response were dissimilar. There was no correlation between PRL and clinical response to haloperidol. RRA and RIA values correlated highly following pimozide but not haloperidol. Our findings lead us to conclude that the RRA technique reflects the plasma level of a drug rather than its central dopamine blocking activity. We also consider that the clinical response to antipsychotic drugs in schizophrenia may be less directly linked to dopamine receptor blockade than has previously been supposed.

During two weeks' treatment of 11 manic patients with pimozide there was close correspondence between the timecourse of improvement in clinical ratings and the rise in plasma prolactin between the second and fourteenth day. There were no significant differences in growth hormone levels during the manic episodes compared to recovery. These findings are discussed in relation to the role of dopamine in the release of prolactin and growth hormone, and in the pathogenesis of mania.