Xanodyne Pharmaceuticals, Inc., maker of the prescription painkillers Darvon and Darvocet, agreed in November 2010 with a Food and Drug Administration (FDA) request to withdraw the medications from the U.S. market. Both products contain the drug propoxyphene, which the FDA has concluded, based on clinical data, places patients at risk of potentially fatal heart arrhythmia (irregular heart rhythm).
The move follows 32 years of controversy over the safety of propoxyphene, which the consumer advocacy organization Public Citizen petitioned the FDA to ban first in 1978 and again in 2006. Britain banned the drug in 2005, followed by the European Union in 2009. In both instances, toxicology data from Florida linking propoxyphene to an unusual number of deaths was cited.
On January 30, 2009, an FDA Advisory Committee met to discuss whether to continue marketing the drug in the United States based on data available at the time. Despite a 14-12 vote by the Committee in favor of taking the drug off of the market, no such action was taken. Instead, the FDA announced in July 2009 that more data was needed to conclusively weigh the benefits of propoxyphene against the risks, and thus required that the manufacturer conduct a new study on the drug’s effects on the heart.
A MAD (multiple-ascending dose) study was then conducted in which healthy volunteers were divided into two groups and given 600 mg and 900 mg, respectively, of propoxyphene for eleven (11) days. During this time, the electrical activity of the subject’s hearts was monitored through electrocardiogram (ECG) technology and other measures. Upon reviewing the data, the FDA determined that: “…propoxyphene can cause significant changes to the electrical activity of the heart, even when the drug is used at therapeutic doses. These changes, prolonged PR interval, widened QRS complex and prolonged QT interval…can increase the risk for serious abnormal heart rhythms.” The FDA further notes that the risk of cardiac effects are subject to sudden change from factors such as sickness, the use of other medications, and a decrease in kidney function. Elderly patients and those with kidney problems are particularly susceptible to propoxyphene-induced arrhythmia.
In determining the safety of a drug, the FDA uses a standard whereby a drug or medical device’s benefits are weighed against its risks. In other words, in the eyes of the FDA, safety is relative, not absolute. According to the FDA, its decision to request the withdrawal of Darvon and Darvocet from the U.S. market is based on the new data which, “…significantly alter propoxyphene’s risk-benefit profile. The drug’s effectiveness in reducing pain is no longer enough to outweigh the drug’s serious potential heart risks.” Specifically, the agency determined that the safety risks of the drug outweigh its benefits for pain relief at recommended doses. Its decision was based not only on the aforementioned study, but also “…other information, including new epidemiological data.” The FDA has also asked generic manufacturers of propoxyphene to comply with a request for market withdrawal, which it expects them to do.
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