FDA Upbeat About Qnexa Ahead of Panel
Briefing documents concerning Vivus' weight-loss drug are released ahead of the advisory committee meeting, and the news is not all bad.
But questions surrounding its safety could keep this weight-loss drug from ever making it out of the gate.
The briefing documents from the FDA were released on Tuesday morning -- two days prior to when the FDA’s Endocrinologic and Metabolic Drugs Advisory Committee is expected to meet to give their expert opinion on whether the weight-loss drug should ultimately hit the market.
Historically, briefing documents can be a great indicator of how the eventual meeting will pan out. These documents usually show how the FDA is thinking and what questions will ultimately be raised when it comes time for an approval decision. (Although the FDA doesn’t have to follow the advice of the panel, they often do.)
(For more information on Advisory Committees, see How to Trade on an FDA Advisory Panel.)
While documents concerning Vivus’ Qnexa, which combines the infamous phentermine (an amphetamine-like appetite suppressant) and topiramate (an anti-seizure medication), clearly state that “all three doses of PHEN/TPM were efficacious for weight loss,” the committee was concerned about five separate safety issues that had arisen during the clinical trials. According to the documents the “adverse events were the major reason for failure to complete the studies.” The instance of adverse events increased with the higher dosages of the drug -- 18% of people on the high dose withdrew from the trial due to these adverse events.
The five things that concerned the committee the most were how the drug would affect pregnant women, the chance of cardiovascular risks, psychiatric events, cognitive events, and metabolic acidosis.
Despite patients being warned during the clinical trials to take extra precautions regarding their sexual behavior, 34 women became pregnant while on the weight-loss drug. Of those women, 19 carried their babies to full term. The babies had no birth defects. Six of those women were taking the placebo at the time. The FDA has concerns that birth defects could be a problem -- topiramate has been linked to this risk in the past (but at two to 34 times the amount included in Qnexa).
As for cardiovascular events, four patients taking Qnexa had heart attacks while zero patients on the placebo were faced with the problem. According to the documents, the FDA is more concerned about the mechanism of action of phentermine, and believes that clinical trials showed little evidence of cardiovascular risks being a problem.
To calm these fears, Vivus is proposing to conduct a large post-marketing cardiovascular outcomes trial of Qnexa if it's approved.
The concern of suicidality also presents itself with topiramate. Johnson & Johnson (JNJ) currently markets topiramate under the brand name Topamax as an anticonvulsant drug and treatment for migraines. The label for the drug includes warnings about suicidal thoughts and an instance of suicide. Although this concern is there, the FDA doesn't seem to think that the risk exists with Qnexa. Yet, other psychiatric concerns were noted.
“While the overall incidence rates were low, it should be pointed out that approximately four to seven times as many subjects randomized to high-dose PHEN/TPM versus placebo discontinued study participation due to anxiety-, sleep-, and depression-related adverse events,” said the documents.
Metabolic acidosis, or the high acidity levels of bodily fluids, is a potential worry due to the inclusion of topiramate. “In the Qnexa Phase III trials, there were no reports of severe metabolic acidosis, but the FDA notes that when the drug is given to a susceptible population -- severe diarrhea, CKD, laxative abuse -- this could become an issue,” notes Leerink Swann analyst Steve Yoo.
Overall, the language in the FDA briefing documents for Qnexa was rather tame and it appears that the drug will likely get the go-ahead. The oversight agency’s qualms with the weight-loss drug largely stemmed from the problems that high doses of its component drugs have caused in the past, and not current evidence that the smaller doses combined in Qnexa caused the same problems.
Vivus will likely have to fit the bill for several post-marketing studies -- a small price to pay if it gets a big piece of the $3 billion obesity pie.
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