Measuring outcome in cocaine clinical trials: a comparison of sweat patches with urine toxicology and participant self-report

Aims To evaluate the advantages of using a sweat patch (PharmCheck?) for detecting cocaine abuse in cocaine‐dependent patients participating in a clinical trial. The utility of the sweat patch was assessed from the following perspectives: the reliability and validity of quantitative sweat patch results, the possible degradation of cocaine to benzoylecgonine (BE) as a function of the length of time that a patch is worn, the completeness of the dataset yielded by thrice‐weekly urine toxicology compared with thrice‐weekly and weekly sweat patches, and the relative costs associated with sweat patch versus urine measures. Design Data were collected during a 10‐week out‐patient clinical trial in which participants wore two sweat patches, one applied every visit and one applied weekly. Urine samples were collected thrice weekly, as were self‐reports of substance use. Setting A multi‐site clinical trial conducted in Boston, Cincinnati and New York, USA. Participants Twenty‐seven participants with comorbid diagnoses of cocaine dependence and adult attention deficit disorder completed the study. Measurements Sweat patch and urine samples were analyzed by standard methods for cocaine and cocaine metabolites. Findings Quantitative sweat patch measures had good reliability in that the correlation between the weekly and per‐visit patches was 0.96 (P < 0.0001). The concurrent validity, as judged by the correlation between quantitative urine BE levels and either weekly (0.76, P < 0.0001) or per‐visit (0.73, P < 0.0001) cocaine sweat patch levels was reasonable. The correlation between the self‐report of cocaine use and these same two patches, however, was lower (0.40, P < 0.05 and 0.30, P < 0.05, respectively). The results revealed no significant degradation of cocaine to BE associated with wearing the patch for a longer time. Finally, the per‐visit patch provided cocaine use data on 80.5% of all study days (a total of 70), while urine toxicology and the weekly patch provided 77.4% and 76.1%, respectively. Conclusions The present findings suggest that the PharmCheck? patch might be an attractive alternative to urine toxicology for use as an outcome measure in cocaine clinical trials.