Possible interference by the reduced haloperidol metabolite with the radioimmunoassay and radioreceptor assay of blood haloperidol.

Serum or plasma samples from haloperidol-treated patients were analyzed by high performance liquid chromatography (HPLC) with electrochemical detection, radioimmunoassay (RIA), and radioreceptor assay (RRA). The HPLC assay allows simultaneous quantitation of the reduced alcohol metabolite of haloperidol. The HPLC and RIA haloperidol results correlated fairly well (r = 0.63), while the HPLC reduced haloperidol and the RIA haloperidol had a weak correlation (r = 0.28). The RRA haloperidol results had a fair correlation with those of the HPLC (r = 0.55), but their correlation with the HPLC reduced haloperidol was almost as good (r = 0.52). The RIA tended to give lower and the RRA higher apparent haloperidol concentrations than the HPLC assay. The results indicate that the reduced haloperidol does not interfere with the RIA procedure used in this study, but it may partially account for higher concentrations obtained with the RRA.