Roche Diagnostics/Boehringer Mannheim Corporation, Pleasanton, CA, USA

These findings were valuable in verifying the accuracy of a recently-developed immunoassay specific for EDDP [CEDIA^® DAU EDDP (Methadone Metabolite) Assay, Boehringer Mannheim Corp.]. Urine samples spiked with high concentrations of methadone were negative by the immunoassay method, but positive by GC/MS. The HPLC method was used to confirm the absence of EDDP in spiked samples, as well as in a small percentage of samples from methadone treatment clinics which, by the CEDIA^® immunoassay method, tested strongly positive for methadone but negative for EDDP. These samples were suspected to result from surreptitious addition of methadone to urine samples by patients who divert and sell the majority of their methadone dosage. In conclusion, alternative methods (i.e., HPLC or LC/MS) should be considered when determining the concentration of EDDP in samples containing high concentrations of methadone.