Detection of methadone, LAAM, and their metabolites by methadone immunoassays

Abstract

I-α-Acetylmethadol (LAAM) was recently approved as a substitute for methadone. LAAM, methadone, and their common metabolite, methadol, are extensively N-demethylated. The structural similarities of LAAM and its metabolites to methadone suggest that they may cross-react in methadone immunoassays. To test this hypothesis, drug-free urine was fortified with LAAM, norLAAM, dinorLAAM, methadol, normethadol, dinormethadol, methadone, 2- ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), or 2-ethyl-5-methyl- 3,3-diphenylpyrroline (EMDP) at 12 concentrations (0.03 to 100 μg/mL). Samples were analyzed using two enzyme immunoassays (Behring Diagnostics, EIA-b; Diagnostic Reagents, EIA-d); a fluorescent polarization immunoassay (Abbott, FPIA); two enzyme-linked immunosorbent immunoassays (Diagnostix, ELISA-d; STC Technologies, ELISA-s); a kinetic microparticles in solution immunoassay (Roche Diagnostic Systems, KIMS); and a radioimmunoassay (Diagnostic Products, RIA). LAAM had high cross-reactivity with ELISA-d (318.3%), RIA (249.5%), EIA-d (100.8%), KIMS (91.1%), and ELISA-s(75.3%). Methadol also displayed relatively high cross-reactivity as follows: EIA-d (97.8%), KIMS (85.4%), ELISA-d (70.3%), and FPIA (37.7%). Successive N- demethylations of LAAM and methadol were associated with loss of cross- reactivity. The methadone metabolites EDDP and EMDP showed little cross- reactivity. These findings suggest that LAAM use could result in positive immunoassay test results when using many of the commercially available methadone immunoassay kits and that confirmation of LAAM and its metabolites should be considered.