The maker of Darvon and Darvocet announced that it would stop marketing the popular painkillers in the U.S. due to a new study linking the active ingredient, known generically as propoxyphene, to serious and sometimes fatal heart rhythm abnormalities or heart arrhythmias. The FDA requested the withdrawal of the drug and has urged doctors to immediately stop prescribing the drugs. The FDA advises patients to continue taking their medication and quickly consult with their physicians to find an alternative treatment.

The FDA called upon the pharmaceutical companies to stop making propoxyphene following a clinical trial in which electrocardiograms showed that the drug altered the heart's electrical activity, potentially causing serious or life-threatening arrhythmias.

An arrhythmia is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. A heartbeat that is too fast is called tachycardia. A heartbeat that is too slow is called bradycardia. Although arrhythmias are harmless, some can be serious or even life threatening. When the heart rate is too fast, too slow, or irregular, the heart may not be able to pump enough blood to the body. The lack of blood caused by an arrhythmia can damage the brain, heart, and other organs, and in the most serious cases, may result in death.

The FDA estimates that the drug has been used by 10 million people in 2009. Propoxyphene was withdrawn from Britain in 2005 and European Union markets in June of 2009 after regulators concluded the risks outweighed pain-relieving benefits.

The safety of the drug has been the subject of controversy for decades. The consumer watchdog group, Public Citizen, petitioned the agency in 1978, and again in 2006, to pull the drug from the market. Public Citizen contends that 1,000 to 2,000 Americans have died from the drug since the U.K. ban, based in part upon data from the state of Florida that found 395 deaths from 2005 to 2009 associated with propoxyphene.

Darvon (generic: propoxyphene) is an opioid used to treat mild to moderate pain. It is manufactured by Xanodyne Pharmaceuticals Inc. The drug is also used in various generic forms. The most popular formulation, which contains the painkiller acetaminophen, is known as Darvocet.

The FDA advises patients who experience an abnormal heart rate or heart rhythm, dizziness, lightheadedness, heart palpitations or fainting to contact a doctor immediately.