Adherence Assessment Using Medication Weight in a Phase IIb Clinical Trial of Difluoromethylornithine for the Chemoprevention of Skin Cancer

Objective: Adherence is a common and essential measurement in clinical trials. This study evaluates the association between participant self-reported study diary records and the weight of the medication vessel at each study visit, in the setting of a phase IIb topical chemoprevention trial. Methods: One hundred and twenty-four eligible participants were randomized to one of four arms [34 to difluoromethylornithine (DFMO) plus triamcinolone, 31 to DFMO plus placebo, 31 to placebo plus triamcinolone, and 28 to double placebo] for 6 months of treatment for actinic keratosis. Adherence was assessed at each clinic visit by weighing each tube of dispensed and returned medication and the participant's study diary. Results: Self-reported adherence was consistently higher than adherence measured by returned medication weight (96.5% versus 71.3%, 94.6% versus 82.4%, 95.3% versus 69.5%, and 95.8% versus 66.8% for DFMO, DFMO placebo, triamcinolone, and triamcinolone placebo, respectively; P < 0.001). Most participants (59.2%) recorded 100% adherence on the study diary; however, using the weight adherence, only 10.2% were completely adherent to the study regimen. Conclusions: Self-reported diary measures seem to overestimate adherence when compared with weighing the returned medication vessel. It is recommended that future clinical trials involving topical applications incorporate medication weights as a primary measure of adherence because it is objective, quantitative, inexpensive, noninvasive, and easy to use.