RADIOIMMUNOASSAY OF DRUGS OF ABUSE IN HAIR .1. METHADONE IN HUMAN HAIR, METHOD ADAPTATION AND THE EVALUATION OF DECONTAMINATION PROCEDURES

A method suitable for the determination of methadone in human hair is presented. Adaptation and evaluation of a solid-phase I-125 radioimmun oassay, designed for the quantitative measurement of methadone in urin e, and development of a pre-analytical wash procedure has enabled a sp ecific, sensitive and accurate analytical procedure to be developed. T he specificity of the antiserum towards other drugs or biologically ac tive compounds is evaluated up to a concentration of 100,000 ng ml(-1) and accuracy covering a range of 0-450 ng ml(-1) is found to be withi n 6% of expected methadone concentrations prepared in both drug free h air extract and urine. Inter-assay relative standard deviation (RSD) a t concentrations of 5.1, 76.0 and 247 ng ml(-1) methadone art 5.5, 2.5 and 3.6% respectively (n = 10) and intraassay RSD at concentrations 2 .3, 25.2 and 217 ng ml(-1) are 5.3, 3.6 and 6.8% (n = 5). The limit of detection is 0.5 ng ml(-1). Extraction of control drug free hair samp les spiked with methadone at concentrations of 100, 250 and 400 ng ml( -1) achieved recoveries of 86, 80 and 89%, respectively. Control hair samples contaminated with methadone an examined under differing wash p rocedures to assess their effectiveness in the removal of methadone co ntaminant. A suitable preanalytical wash regime is proposed for remova l of contaminant derived from external or environmental sources. The m echanics of the wash action and contaminant application to the hair is discussed. It is concluded that the adapted radioimmunoassay and deve loped pre-analytical decontamination procedure is a suitable technique to employ for the measurement of methadone in human hair, be it presc ribed or abused, with concentrations expressed as ng methadone per mg hair.