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

¹ Arizona Cancer Center and ² College of Pharmacy, University of Arizona, Tucson, Arizona

Requests for reprints: Lisa M. Hess, Arizona Cancer Center, University of Arizona, P.O. Box 245024, 1515 North Campbell Avenue, 2964A1 Tucson, AZ 85724. Phone: 520-626-1387; Fax: 520-626-5350. E-mail: hess{at}u.arizona.edu

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.

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				L. M Hess, M. A Raebel, D. A Conner, and D. C Malone Measurement of Adherence in Pharmacy Administrative Databases: A Proposal for Standard Definitions and Preferred Measures Ann. Pharmacother., July 1, 2006; 40(7): 1280 - 1288. [Abstract] [Full Text] [PDF]