The Food and Drug Administration has concluded that a long-term cardiovascular outcome study is necessary to determine the cardiovascular safety of weight loss drug Qnexa (phentermine/topiramate) – and the agency is asking the Endocrinologic and Metabolic Drugs Advisory Committee Feb. 22 for input on whether the study should be conducted before or after approval.
Studies of the drug to date have involved mostly overweight and obese patients with low to moderate baseline cardiovascular (CV) risk, the agency explained in briefing documents for the meeting. As a result, the agency concluded, "it is unknown what the clinical significance of [phentermine/topiramate’s] cardiovascular effects and metabolic effects will be in a higher-risk cardiovascular population with chronic treatment."
Because of that, the agency concluded that "only a long-term, cardiovascular outcome trial can define the effect of [phentermine/topiramate’s] treatment on risk for major adverse cardiovascular events in an obese at-risk population."
When such a trial should be conducted is a discussion question for the panel.
Uncertainty about the cardiovascular safety of Vivus’s Qnexa contributed to a 10-6 vote against approval of the drug when it last went before the advisory committee in 2010.
Twelve of the 16 voting members from that panel will consider Qnexa this time around as well, according to the draft roster for the meeting. Six of the returnees voted in favor of approval in 2010 and six voted no. They will be joined by 10 new voting members.
Contrave CV Study Could Be a Clue
Even if the panel indicates that a postapproval cardiovascular study would be acceptable, that does not guarantee that the FDA will go along.
The agency directed Orexigen Therapeutics to study CV risk in Contrave, a combination of naltrexone and bupropion, in a preapproval trial, although an advisory panel voted 13-7 in favor of approving the drug. The committee voted 11-8, with 1 abstention, that a postmarketing CV trial would be acceptable.
After first announcing it would discontinue development of Contrave, Orexigen reached an agreement with the agency to move forward with an outcomes trial, under a special protocol assessment.
The study, as outlined by Orexigen, provides a glimpse into FDA thinking on what it currently is willing to accept in terms of CV safety in weight loss drugs. The Contrave trial is to enroll 10,000 patients overall, with an estimated background rate of 1%-1.5% annual risk of major cardiovascular events. An interim analysis can be conducted when 87 major adverse CV events occur and serve as the basis for re-filing the Contrave new drug application. The company expects that to come within 2 years and after an enrollment of 7,000.
As for the acceptable risk threshold, the agreement on the Contrave trial is that the upper bound of the 95% confidence interval should exclude those with a risk of 2.0 at the interim and 1.4 at the final analysis. Any patient who does not achieve a predefined weight loss goal after 16 weeks of treatment will discontinue Contrave therapy.
Guidance for diabetes drugs calls on sponsors to exclude an 80% or higher increased risk of CV events before approval. Postapproval CV outcomes trials may be necessary if the risk ratio from a meta-analysis of phase II and phase III studies is between 1.3 and 1.8, but may not be required if the risk ratio is below 1.3.
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