ORLANDO (FRONTLINE MEDICAL NEWS) – Long-term treatment with febuxostat in gout patients with comorbid cardiovascular disease conferred significantly higher risks of both cardiovascular death and all-cause mortality, compared with allopurinol, in the Food and Drug Administration–mandated postmarketing CARES trial, William B. White, MD, reported at the annual meeting of the American College of Cardiology.

CARES (Cardiovascular Safety of Febuxostat or Allopurinol in Patients with Gout and Cardiovascular Disease) was a prospective, double-blind, 320-center North American clinical trial in which 6,190 patients were randomized to febuxostat (Uloric) at 40-80 mg once daily or 200-600 mg of allopurinol once daily. The postmarketing safety study was required by the FDA as a condition of marketing approval for febuxostat in light of preapproval evidence suggestive of a possible increased risk of cardiovascular events, explained Dr. White , professor of medicine and chief of the division of hypertension and clinical pharmacology at the University of Connecticut, Farmington.

The primary study endpoint was a composite of cardiovascular death, MI, stroke, and unstable angina resulting in urgent revascularization. In a modified intention-to-treat analysis at a median of 32 and maximum of 85 months of follow-up, the rate was 10.8% in the febuxostat group and similar at 10.4% in the allopurinol group. So there was no safety issue there.

The warning klaxon sounded when investigators scrutinized the individual components of the primary endpoint. They found that the 4.3% cardiovascular death rate in the febuxostat group was significantly higher than the 3.2% rate in the allopurinol group, representing a statistically significant 34% increase in relative risk. The event curves began to separate roughly 30 months into the trial. Moreover, all-cause mortality was also significantly increased in the febuxostat group, by a margin of 7.8% to 6.4%, for a 22% increase in risk.

The increased cardiovascular mortality in the febuxostat group was driven by a higher adjudicated sudden cardiac death rate: 2.7%, compared with 1.8% in the allopurinol group.

In a prespecified per protocol analysis of cardiovascular events occurring while patients were actually on treatment or within 1 month after discontinuation, the key findings remained unchanged: no between-group difference in the primary composite endpoint, but a 49% increase in the relative risk of cardiovascular death in the febuxostat-treated patients.

A hefty 45% of participants stopped taking their assigned drug early. Dr. White said this isn’t unusual; high dropout rates are common in clinical trials of patients with painful conditions. Because of the high lost-to-follow-up rate, however, the investigators hired a private investigator to scour the country looking for missed deaths among enrollees. This turned up an extra 199 deaths. When those were added to the total, all-cause mortality in the febuxostat group was no longer significantly higher than for allopurinol.

The puzzle over nonfatal events

A puzzling key study finding was that except for cardiovascular death, the other components of the primary composite endpoint – that is, nonfatal MI, nonfatal stroke, and urgent revascularization due to unstable angina – were all either neutral or numerically favored febuxostat.

“That’s been the biggest challenge in the trial: The nonfatal events didn’t go in the same direction as the fatal events. And we don’t have a real mechanism to explain why,” Dr. White told a panel of discussants.

“I scanned the medical literature over the last 4 decades, and I did not see another prospective, randomized, double-blind trial in which mortality was increased when none of the nonfatal events were increased. The finding is unique. Statistically there is only a 4% chance that the mortality finding is wrong,” the cardiologist said.

The CARES leadership included rheumatologists and nephrologists as well as cardiologists. Dr. White said he and the others were at a loss to come up with an explanation for the findings.

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.

“We’re still looking at some correlates that might have an impact. For example, my rheumatologist colleagues feel very strongly that we need to look really extensively at gout flares, even though rates were not that different between the two treatment groups. Gout flares are known to increase oxidative stress and perhaps cause temporary increases in endothelial dysfunction and possibly vasomotor abnormalities,” Dr. White said.

One would think, though, that if gout flares figured in the increase in cardiovascular mortality they would also have been associated with more urgent revascularization for unstable angina, when in fact the rate was actually numerically lower in the febuxostat group, he noted.

Discussant Athena Poppas, MD , director of the Lifespan Cardiovascular Institute at Rhode Island Hospital, Providence, said she couldn’t determine how much of the increased cardiovascular mortality in the febuxostat patients was due to the drug and how much resulted from the suboptimal use of guideline-directed medical therapy across both study arms. At baseline, only 60% of study participants – all by definition at high cardiovascular risk – were on aspirin, just under 75% were on lipid-lowering therapy, 58% were on a beta blocker, and 70% were on a renin-angiotensin system blocker, even though the majority of subjects had stage 3 chronic kidney disease.

Implications of findings and FDA’s next steps

Another discussant, C. Noel Bairey Merz, MD , called the CARES findings “curious.” But despite the lack of a plausible mechanistic explanation for the results, she said, the implications are clear.

“I would conclude that because your modified intention-to-treat as well as your per protocol analyses were consistent for the death endpoint, then despite the high dropout rate, that finding is relatively robust and probably should be used to inform policy,” said Dr. Merz, director of the Women’s Heart Center and the Preventive and Rehabilitative Cardiac Center in the Cedars-Sinai Heart Institute and professor of medicine at the University of California, Los Angeles.

At a press conference, Dr. White said the FDA will spend several months poring over the CARES results and that it would be premature to speculate on what action the agency might take on febuxostat. The drug is prescribed far less frequently than allopurinol for the nation’s estimated 8.2 million gout patients.

“I would certainly be concerned about our findings. However, rheumatologists take care of very ill patients and all the drugs they use have morbidity. So if they’re having substantial efficacy and the person has been on febuxostat for 8 years, I suspect they’re going to continue to give that drug to him,” he said.

Simultaneously with Dr. White’s presentation at ACC 2018, the CARES results were published in the New England Journal of Medicine (N Engl J Med. 2018 Mar 12. doi: 10.1056/NEJMoa1710895 ).

The CARES trial was funded by Takeda. Dr. White reported serving as a consultant to that company and Novartis and receiving research funding from the National Institutes of Health.

SOURCE: White W et al. ACC 18 .