Radioimmunoassay of drugs of abuse in hair. Part 2: The determination of methadone in the hair of known drug users.

This communication addresses the analytical problems associated with the analysis of hair specimens from known users and misusers of the synthetic opioid methadone. An adapted radioimmunoassay and a previously developed preanalytical decontamination procedure have been applied to samples from known drug users. The removal of drugs from the hair surface by washing and the effect of proprietary hair treatments on methadone entrapped in the hair have also been investigated. Pre-analytical washing reduced methadone levels by up to 29%, whilst hair colouration and peroxide bleaching were found to reduce levels by up to 21% and 50% respectively. Methadone assay of extracts from dated hair segments were shown to provide long-term histories of methadone intake, under controlled and non-controlled conditions. Evidence that a dose relationship between hair drug levels and intake may exist is presented. Results of hair analysis, expressed as ng methadone/mg hair, from drug users (range 0.20-10.63) are compared to a pre-determined cut-off of 0.1 ng methadone/mg hair, obtained from the analysis of a known drug free population (n = 23).