propoxyphene and acetaminophen (Darvocet A500; Darvocet-N) - drug class, medical uses, medication side effects, and drug interactions by MedicineNet.com

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Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: propoxyphene and acetaminophen

BRAND NAMES: Darvocet A500; Darvocet-N (Darvocet, Wygesic: These brands no longer are available in the U.S.)

DRUG CLASS AND MECHANISM: Propoxyphene is a strong narcotic pain-reliever and cough suppressant but is weaker than other narcotics such as morphine, codeine, and hydrocodone. The precise mechanism of action is not known but may involve stimulation of opioid receptors in the brain. Propoxyphene increases pain tolerance and decreases discomfort, but the presence of pain is still apparent. In addition to pain reduction, propoxyphene also causes sedation and respiratory depression. Acetaminophen is a non-narcotic analgesic and antipyretic (fever reducer). Acetaminophen relieves pain by elevating the pain threshold. It reduces fever through its action on the heat-regulating center of the brain. The combination of propoxyphene and acetaminophen achieves greater pain relief than either taken separately. For more information on acetaminophen, please see acetaminophen (Tylenol). The FDA first approved propoxyphene/acetaminophen combinations in October 1972.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: propoxyphene/acetaminophen 50/325, 65/650, 100/325, 100/500, and 100 mg/650 mg

STORAGE: Tablets should be stored at room temperature, 15 to 30 C (59 to 86 F).

PRESCRIBED FOR: Propoxyphene/acetaminophen combinations are used for the treatment of mild to moderate pain.

DOSING: The recommended adult dose is 1-2 tablets every 4 hours as needed for relief of pain. Do not exceed six 100/650 mg tablets or twelve 50/325 mg tablets in a 24-hour period.

DRUG INTERACTIONS: Propoxyphene, like other narcotic pain-relievers, increases the effect of drugs that slow brain function, such as alcohol, barbiturates, skeletal muscle relaxants, for example, carisoprodol (Soma) and cyclobenzaprine (Flexeril), and benzodiazepine sedatives, for example, diazepam (Valium) and lorazepam (Ativan). Combined use of muscle relaxants and propoxyphene may lead to greater respiratory depression than either drug alone.

Combining propoxyphene with carbamazepine (Tegretol, Tegretol XR , Equetro, Carbatrol) may have severe effects on the brain including coma.

Since propoxyphene causes constipation, the use of antidiarrheals, for example, diphenoxylate (Lomotil) and loperamide (Imodium), in persons taking propoxyphene, can lead to severe constipation.

Drugs which both stimulate and block opioid receptors for example pentazocine (Talwin), nalbuphine (Nubain), butorphanol (Stadol), and buprenorphine (Buprenex), may reduce the effect of propoxyphene and may precipitate withdrawal symptoms from propoxyphene.

Acetaminophen is metabolized (eliminated by conversion to other chemicals) by the liver. Therefore drugs that increase the action of liver enzymes that metabolize acetaminophen, for example, carbamazepine (Tegretol), isoniazid (INH, Nydrazid, Laniazid), and rifampin (Rifamate, Rifadin, Rimactane), reduce the levels of acetaminophen and therefore may decrease its action. Doses of acetaminophen greater than the recommended doses are toxic to the liver and may result in severe liver damage. The potential for acetaminophen to harm the liver is increased when it is combined with alcohol or drugs that also harm the liver.