EMIT-DAU MONOCLONAL AMPHETAMINE METHAMPHETAMINE ASSAY .1. STEREOSELECTIVITY AND CLINICAL-EVALUATION

The stereoselectivity, cross-reactivity and clinical performance of the EMIT-d.a.u. monoclonal amphetamine(A)/methamphetamine (MA) immunoassay (EM) were evaluated. The cut-off calibrator of the assay was 1000 ng/ml S(+)MA. Analysis of drug-added urines and 72 clinical specimens demonstrated a cut-off for S(+)-amphetamine of approximately 400 ng/ml. The stereoisomeric selectivity of the assay was determined in a concentration vs. response manner by adding pure S(+) or R(-) isomers of A and MA, to drug free urine. The EM assay demonstrated a high selectivity for S(+)-isomers with only one of 16 urine specimens collected following excessive use of nasal inhalers yielding a positive result. This specimen contained 6000 ng/ml R(-) MA. Five-hundred clinical urine specimens were simultaneously analyzed for A or MA by the EM and EMIT-d.a.u. polyclonal (EP) amphetamine assay with 131 positive results confirmed by GC/MS. In five specimens negative by EM while positive by EP, MA was present at concentrations below the 1000 ng/ml cut-off. Two ME false positive results were apparently caused by chlorpromazine (CPZ) metabolites. A study of other phenothiazines or their metabolites gave no false positive results. The possible cross reactivity of the EM assay was further studied for phenylisopropytamine analogs or drugs previously reported to react with the EP assay. The EM assay showed much less cross-reactivity than EP to all drugs tested.