Late last year the Food and Drug Administration (FDA) banned the drugs Darvon and Darvocet, also known by the generic propoxyphene, from the U.S. market because new data showed that people who used the drug were at an increased risk for serious abnormal heart rhythms. Here’s a closer look at that data and the problems associated with propoxyphene-containing drugs:
The new data came from a 2007 Multiple Ascending Dose (MAD) Study Review which was designed to determine an appropriate dose that could be used in a definitive cardiac study. The drug had just received a black box warning because of numerous reports of intentional and unintentional deaths from overdose. Conducted by the drugs’ maker, Xanodyne Pharmaceuticals, the study involved 18 healthy volunteers who received either a 600 mg dose or a 900 mg dose of propoxyphene for 11 days.
The results of that study demonstrated that even when propoxyphene was taken at the recommended doses, there were significant changes to the electrical activity of the heart including prolonged PR interval, widened QRS complex and prolonged QT interval. These changes, which can be seen on an ECG, can increase the risk for serious abnormal heart rhythms, which can lead to sudden death.
Patients at greater risk for complications from propoxyphene include those with impaired kidney function because they cannot eliminate propoxyphene from the body as well as patients with healthy kidneys. This can lead to an accumulation of the drug in the body. Patients taking other medications that can affect the heart or the breakdown of propoxyphene are also at higher risk.
Patients who are currently taking propoxyphene should contact their doctor as soon as possible to discuss switching to an alternative pain medication. Propoxyphene may need to be tapered rather than stopped immediately to reduce the risk of other side effects including nausea, vomiting, diarrhea, anxiety and shivering.