Detection of drug use in a methadone maintenance clinic: sweat patches versus urine testing

Aims. To evaluate the novel use of sweat patches hi: outpatients attending a methadone maintenance clinic. Design. Assessment of inter-patch reliability and validity of patch results compared to urine tests at the start and end of the patch period. Semi-structured questionnaire on patients' opinion of the patches. Randomized cross-over trial comparing illicit drug use during the week, that the patch was worn with a control period. Setting. Methadone maintenance outpatient clinic in a deprived urban area. Participants. Forty-eight patients with a diagnosis of opiate addiction prescribed methadone for a median of 5 years. Measurements. Analysis of urine and patch tests by standard methods for methadone, opiates: morphine (heroin metabolite) and benzoylecgonine (cocaine metabolite). Findings. There was good inter-patch reliability between arm and side patches for methadone (all positive), opiates (k = 0.8) and morphine (k = 1.0) but only moderate agreement for benzoylecgonine (k = 0.49). There was good agreement between the sweat patches and urine tests for methadone (all positive), opiates (k = 1.00) and morphine (k.= 0.8), but again only moderate agreement for benzoylecgonine (k = 0.50). The patches were well tolerated and the main side effect was minor irritation. The majority of men preferred a urine test while more women preferred a swear patch. There was no evidence of reduced use of illicit drugs during the period that the patch was worn. Conclusion. Sweat patches are reliable and give valid results for patients on maintenance methadone. There are few side effects and it is practical to use them in busy outpatient clinics. They are preferred by some patients but there was no evidence that they altered behaviour.