The synthetic opiate dextropropoxyphene, formerly sold in the United States, Canada, and Europe under the brand name Darvocet®, was used as a painkiller, a cough suppressant, a local anesthetic, and a treatment for restless leg syndrome. There are a number of factors that could affect the dosage level of this medication, particularly the concurrent use of several drugs that could interact it, the presence of opiate cross-tolerance, the weight of the patient, the severity of pain, and the liver and kidney health of the patient. As with any opiate-based painkiller, the initial Darvocet® dosage should be adjusted as needed under the supervision of a physician to adequately manage the patient's symptoms.
When using Darvocet® to manage pain, it is important to remember that the European Medicines Agency's review of Darvocet®'s efficacy found that the medication was a weak painkiller — less effective in fact than acetaminophen. The manufacturer's Darvocet® dosage recommendations, however, were that a single capsule containing 100 mg of propoxyphene napsylate and 650 mg of acetaminophen be given every four hours as required for pain management. No more than six of these tablets can be give per day due to the risk of acetaminophen overdose. If using Darvocet®-N 50, a weaker form containing only 50 mg of propoxyphene napsylate and 325 mg acetaminophen, then the dosage is exactly double the standard dosage. No more than 12 of these weaker tablets can be taken within a 24 hour period.
A number of medications may produce dangerous drug interactions when taken with Darvocet®, particularly other painkillers or medications that may contain additional acetaminophen. Patients switched to this medication from an alternative opioid painkiller will need to be closely monitored to ensure that effective pain management is achieved, while the dose of the previous painkiller is slowly reduced and the Darvocet® dosage is gradually increased. Since the drug is metabolized by the liver enzyme cytochrome P450 3A4, the use of drugs that inhibit this enzyme alongside it may necessitate a decrease in Darvocet® dosage or risk overdose. If discontinuing a medication that increases the level of cytochrome P450 3A4, the Darvocet® dosage may need to be decreased for the same reason.
Patients with diminished levels of kidney or liver function may also require a lower Darvocet® dosage. When administering the medication to these patients, the lowest possible dose should be given and careful attention should be paid to its effects. Similar caution should be given when using Darvocet® in elderly or debilitated patients.
Darvocet® was removed from the market due to the frequency with which fatal disruptions to heart rhythms and acetaminophen overdoses occurred. The recall has impacted right to die groups, many of which had advocated its use for assisted suicide as a substitute for barbituate-based sleeping pills after their withdrawal. Despite these risks, dextropropoxyphene is still available by prescription in Australia in the medications Di-gesict®, Capadext®, Paradext®, and Doloxenet®.