PROPOXYPHENE

Toxicity

Coma, respiratory depression, circulatory collapse, and pulmonary edema. Seizures occur more frequently in patients with propoxyphene intoxication than in those with opiate intoxication. LD50=230mg/kg (orally in rat, Emerson)

The Uses of PROPOXYPHENE

Analgesic.

Background

Dextropropoxyphene is an opioid analgesic manufactured by Eli Lilly and Company. It is used in the symptomatic treatment of mild pain. It displays antitussive and local anaesthetic actions. Due to the risk of cardiac arrhythmias and overdose, possibly leading to death, dextropropoxyphene has been withdrawn from the market in Europe and the United States. The drug is often referred to as the general form, "propoxyphene", however only the dextro-isomer (dextropropoxyphene) has any analgesic effect. The levo-isomer appears to exhibit a very limited antitussive effect.

Indications

For the relief of mild to moderate pain.

Definition

ChEBI: The (1S,2R)-(+)-diastereoisomer of propoxyphene.

brand name

Darvon-N (Xanodyne).

Biological Functions

Propoxyphene (dextropropoxyphene; Darvon) is structurally related to methadone but is much less potent as an analgesic. Compared with codeine, propoxyphene is approximately half as potent and is indicated for the treatment of mild pain. It is not antipyretic or antiinflammatory like aspirin and is less useful than aspirin in most cases of mild pain. Toxicity from propoxyphene, especially in combination with other sedatives, such as alcohol, has led to a decrease in its use. Death following ingestion of alcohol in combination with propoxyphene can occur rapidly (within 20 minutes to 1 hour). The drug is not indicated for those with histories of suicide or depressive illnesses.
Like meperidine, propoxyphene has an active metabolite, norpropoxyphene, that is not analgesic but has excitatory and local anesthetic effects on the heart similar to those of quinidine. Use of the drug during pregnancy is not safe.Teratogenic effects have been observed in newborns, as have withdrawal signs at birth. As with morphine, propoxyphene requires adequate hepatic and renal clearance to prevent toxicity and drug accumulation. It is thus contraindicated in the elderly patient and those with renal or liver disease.
Propoxyphene interacts with several drugs. The use of sedatives in combination with propoxyphene can be fatal. In addition, the metabolism of the drug is increased in smokers due to induction of liver enzymes. Thus, smokers may require a higher dose of the drug for pain relief. Propoxyphene enhances the effects of both warfarin and carbamazepine and may increase the toxicity associated with both drugs, such as bleeding and sedation, respectively.
The abuse liability of propoxyphene is low because of the extreme irritation it causes at the site of injection. Oral use is the preferred route of administration for this reason.

General Description

Most of the structural changes to the methadone skeletonresulted in compounds with decreased opioid potencies, thusmost of these compounds, with the exception of LAAM werenot developed. Propoxyphene is a derivative of methadonemarketed in 1957 as the enantiomerically pure (2S, 3R)-4-(Dimethylamino)-3-methyl-1,2,-diphenyl-2-butanol propionate(ester). It is only about 1/10th as potent as morphine asan analgesic yet retains all the same opioid adverse effects.One propoxyphene 65-mg capsule has the same analgesic effectof 650 mg of aspirin or 1,000 mg of acetaminophen, thusoverdoses of propoxyphene can occur if patients do not followthe prescribed dose. Between 1981 and 1999, 2,110 accidentaldeaths were reported because of propoxyphene.Propoxyphene and all propoxyphene combination productsare listed using the Beers criteria as medications to avoid inpatients older than 65 years of age. The metabolism ofpropoxyphene also contributes to the potential dangers of thedrug. Propoxyphene is metabolized via N-demethylation toform norpropoxyphene. Norpropoxyphene has been shownto build up in cardiac tissues and result in naloxone-insensitivecardiotoxicity. The weak analgesic action and potentialrisk to the patient have some health practitioners advocatingto remove all drugs containing propoxyphene from the market.The hydrochloride salt is marketed as Darvon, the napsylatesalt as Darvon-N, both salts are also available combinedwith acetaminophen (Darvocet, Darvocet-N) and apropoxyphene, aspirin, caffeine product is also available.

Pharmacokinetics

Propoxyphene, a synthetic opiate agonist, is structurally similar to methadone. Its general pharmacologic properties are those of the opiates as a group. The analgesic effect of propoxyphene is due to the d-isomer, dextropropoxyphene. It binds to the opiate receptors and leads to a decrease of the perception of pain stimuli. Propoxyphene possesses little to no antitussive activity and no antipyretic action.

Safety Profile

Poison by ingestion, intraperitoneal, subcutaneous, and intravenous routes. Human systemic effects by ingestion: change in cardiac rate, respiratory depression, and coma. When heated to decomposition it emits toxic fumes of NOx.

Metabolism

Hepatic