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Comment & Response
July 13, 2020

Changed Primary Outcome Between Trial Registration and Publication—Reply

Author Affiliations
  • 1Addiction Sciences Division, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston
JAMA Intern Med. Published online July 13, 2020. doi:10.1001/jamainternmed.2020.2173

In Reply Kleinman and Ostacher have indicated concern about the choice of end points for our recent clinical trial of gabapentin in those with alcohol use disorder (AUD).1 One concern was the use of the percentage of disialo carbohydrate-deficient transferrin (%dCDT) biomarker of heavy drinking to adjust the verbal reports of drinking provided during the trial, a procedure not detailed a priori. Unfamiliarity with this biomarker of alcohol consumption might underlie some of this concern. In fact, when assayed by the International Federation of Clinical Chemistry–recommended high-performance liquid chromatography assay,2 a %dCDT value above 1.7% has almost 100% specificity for heavy alcohol consumption, and, by extension, any alcohol consumption. Prior to knowing the participant study-drug assignments and based on their having positive %dCDT values above 1.7% during the trial, we judged that several participants had misreported their drinking status, not an unusual occurrence in both clinical trials and practice. We had to make a choice regarding which bias was more acceptable: to just report the verbally reported drinking in these cases, which we judged to be erroneous, or to adjust their treatment outcome to a heavy-drinking and/or nonabstinent status. While we judged the latter to be more valid, we also reported the nonadjusted verbally reported drinking status as well, thereby allowing readers to draw their own conclusions. All analyses on both the adjusted and the nonadjusted drinking outcomes were done prior to breaking the blind on study medication assignments. Of note, in another recent clinical trial by our group,3 we had reported that %dCDT values provided equal, or better, treatment effect sizes compared with verbally reported drinking status, attesting to its value as an important biomarker to consider in judging efficacy in alcohol clinical trials.

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