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.