Detecting cocaine use through sweat testing: multilevel modeling of sweat patch length-of-wear data.

Although urine analysis remains the standard for detection of drugs of abuse, sweat patches provide a convenient alternative that avoids some of the problems with drug testing such as violations of privacy in observed urination, possibility of disease transmission, and transport of noxious fluids. This study examined minimum length of wear necessary to detect recent or concurrent cocaine use in a convenience sample of active cocaine users and also differences in analyte concentrations with increasing longer-term wear. Twenty-seven subjects (22 active drug users and 5 comparison subjects who did not use drugs) wore short-term ((1/2)h, 1 h, 1(1/2) h, and 2 h), then long-term patches (1, 3, 7, and 14 day). Short- and long-term patches were identical except for duration of wear. The predominant analyte found was cocaine, followed by benzoylecgonine, then ecgonine methylester. The minimum duration that patches must be worn to detect recent or concurrent cocaine use in this sample is more than 2 h and less than or equal to 1 day. Analyte concentrations increase significantly with increasing lengths of wear. However, increases between the one-week and two-week patches were significant for benzoylecgonine only.