Here is background and historical information from the FDA about Darvocet and Darvon:
Following receipt of a Citizen Petition requesting the withdrawal of propoxyphene-containing products from the United States market, FDA convened an Advisory Committee meeting on January 30, 2009. After presentations by FDA, the petitioner, and the company reviewing the efficacy and safety data from the propoxyphene drug applications, the literature and postmarketing safety databases, the committee voted by a narrow margin (14-to-12) against the continued marketing of propoxyphene products.
Those who voted for propoxyphene to remain on the market advised requiring improved labeling, particularly with warnings about use in elderly patients and about use with concomitant opioids or alcohol. Finally, there was general agreement that additional information about the cardiac effects of propoxyphene would be relevant in further weighing the risk and benefit. As a result, under new authorities given to FDA by the Food and Drug Administration Amendments Act (FDAAA), the agency required the drug manufacturer to conduct a thorough QT study to formally evaluate the effects of propoxyphene on cardiac electrophysiology. In order to determine a safe supratherapeutic dose to incorporate into the Thorough QT study, FDA required the drug manufacturer to first conduct a multiple-ascending dose (MAD) study.
The MAD study was a randomized, double-blind, placebo-controlled sequential multiple-ascending dose study of propoxyphene for 11 days. The study was conducted in healthy volunteers. The first cohort of study subjects was dosed with a total daily dose of 600 mg of propoxyphene (the maximum labeled dose) and the second cohort was dosed with a total daily dose of 900 mg. Additional doses were planned, however the study was placed on clinical hold due to safety concerns. Study subjects were monitored with telemetry and intermittent ECG recordings, comparable to the monitoring that would occur during a Thorough QT study.
The drug manufacturer has submitted to FDA the results from the 600 mg and 900 mg cohorts.
Significant QTc interval prolongations were observed with the propoxyphene 600 mg and 900 mg dose levels. With the 600 mg daily dose, at steady state on Treatment Day 11, the largest mean change of QTcF* (ΔΔQTcF) was 29.8 milliseconds (ms), which occurred 7 hours after the last dose; with the 900 mg dose the largest mean change was 38.2 ms, which occurred 2 hours after the last dose. It is recognized in the International Conference on Harmonisation (ICH) E14 Guideline1 that drugs that prolong the mean QT/QTc interval by >20 ms have a substantially increased likelihood of being proarrhythmic. In addition, a dose-dependent prolongation of PR and QRS intervals was observed in the study.
Because the elderly and patients with renal insufficiency have a reduction in the clearance of propoxyphene and its cardioactive metabolite, norpropoxyphene, through the kidneys, these populations can be especially susceptible to proarrhythmic effects of the drug.
FDA has concluded that the safety risks of propoxyphene outweigh its limited benefits2-6 for pain relief at recommended doses.
*QTcF is the QT interval corrected for heart rate using the Fridericia formula (cubic root – QTcF = QT/RR1/3).
- Guidance for Industry – E14 Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic Drugs. October 2005.
- Beaver WT. Mild analgesics. A review of their clinical pharmacology. II. Am J Med Sci. 1966;251:576-99 concl.
- Lasagna L. The clinical evaluation of morphine and its substitutes as analgesics. Pharmacol Rev. 1964;16:47-83.
- Collins SL, Edwards JE, Moore RA, McQuay HJ. Single dose dextropropoxyphene, alone and with paracetamol (acetaminophen), for postoperative pain. Cochrane Database Syst Rev. 2000;(2):CD001440.
- Collins SL, Edwards JE, Moore RA, McQuay HJ. Single-dose dextropropoxyphene in post-operative pain: a quantitative systematic review. Eur J Clin Pharmacol. 1998;54:107-12.
- Veterans Health Administration Pharmacy Benefits Management Strategic Healthcare Group and Medical Advisory Panel. Review of the Efficacy and Safety of Propoxyphene. March 2006.