Serum haloperidol determinations in psychiatric patients. Comparison of methods and correlation with serum prolactin level.

Twenty-one serum samples from 11 schizophrenic patients receiving long-term haloperidol therapy were analyzed for haloperidol concentrations by two different radioimmunoassays (RIAs) and gas chromatography (GC). There was a good correspondence between the RIA and GC values over a wide range of drug concentrations. However, compared with the specific GC technique, both RIA methods overestimated haloperidol concentrations, reflecting differences in the specificities of the two RIA antibodies. One of the RIA methods had the requisite specificity for application to patients treated with long-term haloperidol therapy, although further methodological refinement will be required for its general clinical application. Haloperidol values determined by GC and RIA analyses correlated highly with prolactin concentrations in the same samples, suggesting that the usefulness of prolactin measurement as an "in vivo bioassay" for circulating levels of haloperidol should be further explored.