Patients in the febuxostat arm were significantly more likely to achieve serum urate levels below 6 and 5 mg/dL. Their flare rate was 0.68 events per person-year, similar to the 0.63 per person-year rate in the allopurinol group.
Among the pieces of the study puzzle: The majority of cardiovascular deaths occurred in patients who were no longer on therapy, yet investigators could find no evidence of a legacy effect. The mortality risk was 2.3-fold greater with febuxostat than with allopurinol among patients on NSAID therapy, but there was no significant between-group difference among patients not taking NSAIDs. There was a trend for more cardiovascular deaths with febuxostat than allopurinol among patients not on low-dose aspirin. And the cardiovascular mortality was 2.2-fold greater in the febuxostat arm than with allopurinol in patients on colchicine during the study.
Notably, prior to febuxostat’s marketing approval there were extensive studies of the drug’s potential effect on left ventricular function, thrombotic potential, possible arrhythmogenic effects, and impact upon atherosclerosis. Among these investigations was a QT-interval study conducted using febuxostat doses four times higher than the maximum therapeutic dose, which was prescient given the increased sudden cardiac death rate in the subsequent CARES trial. Yet no concerning signals were seen in any of this work, he continued.