The SRPHK1 outcome measure for cocaine-dependence trials combines self-report, urine benzoylecgonine levels, and the concordance between the two to determine a cocaine-use status for each study day

BackgroundThere is currently no FDA-approved medication for cocaine dependence and no standard primary outcome measure for reduction of cocaine use in cocaine-dependence trials. The ability to detect a significant medication effect will depend, in part, on the primary outcome measure utilized. The goal of the present paper is to compare self-report or either of two urine toxicology measures used alone to a relatively new measure – the SRPHK1 – which combines self-report, quantitative urine benzoylecgonine levels, and an estimate of the concordance between the two to determine the cocaine-use status of each study day.MethodDatasets from two separate randomized, placebo-controlled cocaine-dependence trials were used to compare four cocaine-use outcome measures.ResultsThe two data sets yielded very similar findings and suggest that the combined measure is associated with significantly fewer missing data than urine toxicology and that estimated cocaine use varied significantly depending on which measure was used, with the lowest use estimate being yielded by self-report, the highest by the two urine toxicology measures evaluated, and an intermediate value obtained using the combined measure. The results also suggest that the concordance between self-report and urine toxicology is around 90% at the beginning of the clinical trial but decreases to around 75% by the end of the trial.ConclusionBy combining the objectivity of urine toxicology with the reduced incidence of missing data characteristic of self-report, the SRPHK1 may provide advantages over self-report or urine toxicology measures used alone. In any case, the SRPHK1 provides an interesting complement to these other outcome measures and may warrant further evaluation.