Application and validation of a urinary methadone metabolite (EDDP) immunoassay to monitor methadone compliance

A total Of 1381 urine specimens were screened using a Microgenics CEDIA uri nary primary methadone metabolite (2-ethylidene-1,5-dimethyl-3,3-diphenylpy rrolidine; EDDP) immunoassay (cut-off calibrator concentration of 100 mu g/ L) in combination with a Dade Behring EMIT urinary methadone immunoassay (c ut-off calibrator concentration of 300 mu g/L). Of these, 642 (46%) were fo und to be positive using the EDDP assay but only 541 (39%) were found to be positive by the methadone assay. Out of the 108 specimens which were EDDP-positive but negative by the metha done assay, 47 (7%) could not be confirmed as positive using the routine in -house method of gas chromatography incorporating nitrogen-specific detecti on. Of these 47 results, 38 were re-screened using a more sensitive gas chr omatography-mass spectrometry (GC-MS) technique, which demonstrated the pre sence of EDDP in every case. There was insufficient specimen to analyse the remaining nine samples. There were seven specimens which gave negative res ults by the EDDP and GC-MS assays but which had methadone concentrations ra nging from 4000 to 37500 mu g/L. These were therefore presumed to be 'spike d' with methadone, i.e. to have had methadone added to the specimen to yiel d positive screening results and simulate compliance. It is concluded that the Microgenics CEDIA EDDP assay is a sensitive and re liable technique to determine the compliance of subjects prescribed methado ne for opiate detoxification and maintenance.