Plasma haloperidol levels drawn at neuroleptic threshold doses: A pilot study
The daily haloperidol doses of 33 newly admitted, acutely psychotic schizophrenic patients were rapidly adjusted to a point at which slight hypokinesia-rigidity first appeared on clinical examination (the neuroleptic threshold). The mean daily haloperidol dose at which the neuroleptic threshold was crossed was 4.2 ± 2.4 mg/day. The plasma haloperidol levels obtained at these neuroleptic threshold doses clustered around a mean of 4.9 ± 2.9 ng/ml. This plasma haloperidol level distribution extensively overlaps the proposed lower boundaries for the therapeutically effective range of plasma haloperidol levels, but it is below the range in which coarse extrapyramidal side effects appear in high frequency (>10 ng/ml). Sixty-seven percent of the authors' patients demonstrated moderate or greater therapeutic improvement within 3 weeks of treatment at neuroleptic threshold doses, a therapeutic efficacy rate identical to that expected with standard neuroleptic doses. The authors propose that the neuroleptic threshold is a readily available clinical marker which identifies a range of plasma haloperidol levels capable of producing therapeutic response with minimal associated coarse extrapyramidal side effects.