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FDA advisory decision highlights some problems inherent in pragmatic trials.

AMEETING OF AN ADVISORY COMmittee to the US Food and Drug Administration (FDA) regarding a drug to minimize stroke risk for patients with atrial fibrillation illuminated the difficulties of gleaning knowledge from pragmatic trials—studies designed to determine the effectiveness of therapies in everyday practice. In September, the FDA’s Cardiovascular and Renal Drugs Advisory Committee voted 9 to 2, with 1 abstention, to recommend that the agency approve rivaroxaban, an oral antithrombin, as an alternative treatment to warfarin, a vitamin K antagonist, for patients with atrial fibrillation. The FDA generally goes along with advisory committee recommendations. Rivaroxaban’s status as an alternative treatment is based on results from the Stroke Prevention Using the Oral Direct Factor Xa Inhibitor Rivaroxaban Compared With Warfarin in Patients With Nonvalvular Atrial Fibrillation (ROCKET AF) trial. This double-blind trial involved 14 264 patients with nonvalvular atrial fibrillation at increased risk for stroke who were randomized to a dose of 20 mg/d of the drug or to dose-adjusted warfarin. In that trial, researchers found rivaroxaban to be noninferior to warfarin for the prevention of stroke or systemic embolism (Patel MR et al. N Engl J Med. 2011;365[10]:883-891). But the FDA itself, in a briefing document submitted to the advisory committee, stated caveats that raised questions about the rigor of the ROCKET AF trial. The document’s authors said findings from ROCKET AF were not adequate to determine whether rivaroxaban was as effective for its proposed indication compared with warfarin when the existing treatment is used skillfully. The FDA’s concerns centered on how warfarin was used in ROCKET AF. To evaluate proper dosing of warfarin, physicians use a surrogate measure called time in therapeutic range (TTR). The FDA said the median TTR for warfarin in general use is about 65%,