Darvon and Darvocet Description

At the request of the U.S. Food and Drug Administration (FDA), Xanodyne Pharmaceuticals Inc., makers of Darvon and Darvocet, pulled the drug off the market. The FDA also informed generic makers of the drug propoxyphene to voluntary stop production as well. Propoxyphene is an opioid used to treat mild to moderate pain. First approved by the FDA in 1957, propoxyphene is sold by prescription under various names both alone (e.g., Darvon) or in combination with acetaminophen (e.g., Darvocet). The recall was issued after clinical data demonstrated propoxyphene puts patients at risk of potentially serious or even fatal heart rhythm abnormalities.

As a result of the data, combined with information including new epidemiological data, the FDA concluded that the risks of the medication outweigh the benefits. According to a press release "The FDA is pleased by Xanodyne's decision to voluntarily remove its products from the U.S. market," said John Jenkins, M.D., director of the Office of New Drugs in the FDA's Center for Drug Evaluation and Research (CDER). "These new heart data significantly alter propoxyphene's risk-benefit profile. The drug's effectiveness in reducing pain is no longer enough to outweigh the drug's serious potential heart risks."

The following are some of the drugs that contain propoxyphene:

  • Darvocet A500
  • Darvocet-N
  • Darvocet-N 100
  • Darvocet-N 50
  • Darvon
  • Darvon-N 100
  • Darvon-N

Darvon-N Description

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Darvon-N contains propoxyphene napsylate, USP which is an odorless, white crystalline powder with a bitter taste. It is very slightly soluble in water and soluble in methanol, ethanol, chloroform, and acetone. Chemically, it is (αS,1R)-α-[2-(Dimethylamino)-1-methylethyl]-α-phenylphenethyl propionate compound with 2-naphthalenesulfonic acid (1:1) monohydrate, which can be represented by the accompanying structural formula. Its molecular weight is 565.72

Propoxyphene napsylate differs from propoxyphene hydrochloride in that it allows more stable liquid dosage forms and tablet formulations. Because of differences in molecular weight, a dose of 100 mg (176.8 μmol) of propoxyphene napsylate is required to supply an amount of propoxyphene equivalent to that present in 65 mg (172.9 μmol) of propoxyphene hydrochloride.

Each tablet of Darvon-N contains 100 mg (176.8 μmol) propoxyphene napsylate. The tablet also contains cellulose, cornstarch, iron oxides, lactose, magnesium stearate, silicon dioxide, stearic acid, and titanium dioxide.

Darvon-N - Clinical Pharmacology

Pharmacology
Propoxyphene is a centrally acting opiate analgesic. In vitro studies demonstrated propoxyphene and the metabolite norpropoxyphene inhibit sodium channels (local anesthetic effect) with norpropoxyphene being approximately 2-fold more potent than propoxyphene and propoxyphene approximately 10-fold more potent than lidocaine. Propoxyphene and norpropoxyphene inhibit the voltage-gated potassium current carried by cardiac rapidly activating delayed rectifier (hERG) channels with approximately equal potency. It is unclear if the effects on ion channels occur within therapeutic dose range.

Pharmacokinetics Absorption

Peak plasma concentrations of propoxyphene are reached in 2 to 2.5 h. After a 65-mg oral dose of propoxyphene hydrochloride, peak plasma levels of 0.05 to 0.1 μg/mL for propoxyphene and 0.1 to 0.2 μg/mL for norpropoxyphene (major metabolite) are achieved. Repeated doses of propoxyphene at 6 h intervals lead to increasing plasma concentrations, with a plateau after the ninth dose at 48 h. Propoxyphene has a half-life of 6 to 12 h, whereas that of norpropoxyphene is 30 to 36 h.

Distribution
Propoxyphene is about 80% bound to proteins and has a large volume of distribution, 16 L/kg.

Metabolism
Propoxyphene undergoes extensive first-pass metabolism by intestinal and hepatic enzymes. The major route of metabolism is cytochrome CYP3A4 mediated N-demethylation to norpropoxyphene, which is excreted by the kidneys. Ring hydroxylation and glucuronide formation are minor metabolic pathways.

Excretion
In 48 h, approximately 20 to 25% of the administered dose of propoxyphene is excreted via the urine, most of which is free or conjugated norpropoxyphene. The renal clearance rate of propoxyphene is 2.6 L/min.

SPECIAL POPULATIONS Geriatric Patients

After oral administration of propoxyphene in elderly patients (70-78 years), much longer half-lives of propoxyphene and norpropoxyphene have been reported (propropoxyphene 13 to 35 h, norpropoxyphene 22 to 41 h). In addition, the AUC was an average of 3-fold higher and the Cmax was an average of 2.5-fold higher in the elderly when compared to a younger (20-28 years) population. Longer dosage intervals may be considered in the elderly because the metabolism of propoxyphene may be reduced in this patient population. After multiple oral doses of propoxyphene in elderly patients (70-78 years), the Cmax of the metabolite (norpropoxyphene) was increased 5-fold.

Pediatric Patients
Propoxyphene has not been studied in pediatric patients.

Hepatic Impairment
No formal pharmacokinetic study of propoxyphene has been conducted in patients with mild, moderate or severe hepatic impairment.

After oral administration of propoxyphene in patients with cirrhosis, plasma concentrations of propoxyphene were considerably higher and norpropoxyphene concentrations were much lower than in control patients. This is presumably because of a decreased first-pass metabolism of orally administered propoxyphene in these patients. The AUC ratio of norpropoxyphene: propoxyphene was significantly lower in patients with cirrhosis (0.5 to 0.9) than in controls (2.5 to 4).

Renal Impairment
No formal pharmacokinetic study of propoxyphene has been conducted in patients with mild, moderate or severe renal impairment.

After oral administration of propoxyphene in anephric patients, the AUC and Cmax values were an average of 76% and 88% greater, respectively. Dialysis removes only insignificant amounts (8%) of administered dose of propoxyphene.

Drug Interactions
The metabolism of propoxyphene may be altered by strong CYP3A4 inhibitors (such as ritonavir, ketoconazole, itraconazole, troleandomycin, clarithromycin, nelfinavir, nefazadone, amiodarone, amprenavir, aprepitant, diltiazem, erythromycin, fluconazole, fosamprenavir, grapefruit juice, and verapamil) leading to enhanced propoxyphene plasma levels. On the other hand, strong CYP3A4 inducers such as rifampin may lead to enhanced metabolite (norpropoxyphene) levels.

Propoxyphene is also thought to possess CYP3A4 and CYP2D6 enzyme inhibiting properties. Coadministration with a drug that is a substrate of CYP3A4 or CYP2D6, may result in higher plasma concentrations and increased pharmacologic or adverse effects of that drug.

INDICATION
Darvon-N is indicated for the relief of mild to moderate pain.

Contraindications

Darvon-N is contraindicated in patients with known hypersensitivity to propoxyphene.
Darvon-N is contraindicated in patients with significant respiratory depression (in unmonitored settings or the absence of resuscitative equipment) and patients with acute or severe asthma or hypercarbia.
Darvon-N is contraindicated in any patient who has or is suspected of having paralytic ileus.

What is Darvocet?

Darvocet contains a combination of propoxyphene and acetaminophen. Propoxyphene is in a group of drugs called narcotic pain relievers. Acetaminophen is a less potent pain reliever and a fever reducer that increases the effects of propoxyphene.
Darvocet is used to relieve mild to moderate pain with or without fever.
Darvocet may also be used for other purposes not listed in this medication guide.

Important information about Darvocet

Avoid drinking alcohol while taking Darvocet. Alcohol may increase your risk of liver damage while taking acetaminophen. Propoxyphene may be habit-forming and should be used only by the person it was prescribed for. Keep the medication in a secure place where others cannot get to it.

Do not use Darvocet if you have taken an MAO inhibitor such as furazolidone (Furoxone), isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam), or tranylcypromine (Parnate) in the last 14 days. Serious, life threatening side effects can occur if you use Darvocet before the MAO inhibitor has cleared from your body.

Do not take Darvocet in larger amounts, or use it for longer than recommended by your doctor. Tell your doctor if the medicine seems to stop working as well in relieving your pain.

Before taking Darvocet?

Do not use Darvocet if you are allergic to acetaminophen (Tylenol) or propoxyphene. Propoxyphene may be habit-forming and should be used only by the person it was prescribed for. Propoxyphene should never be shared with another person, especially someone who has a history of drug abuse or addiction. Keep the medication in a secure place where others cannot get to it.

Do not use Darvocet if you have taken an MAO inhibitor such as furazolidone (Furoxone), isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam), or tranylcypromine (Parnate) in the last 14 days. Serious, life threatening side effects can occur if you use Darvocet before the MAO inhibitor has cleared from your body.

If you have any of these other conditions, you may need a dose adjustment or special tests to safely take Darvocet:

  • asthma, COPD, sleep apnea, or other breathing disorders;
  • liver or kidney disease;
  • a history of head injury or brain tumor;
  • a gallbladder or pancreas disorder;
  • low blood pressure
  • a stomach or intestinal disorder;
  • mental illness; or
  • a history of drug or alcohol addiction.

Tell your doctor if you drink more than three alcoholic beverages per day or if you have ever had alcoholic liver disease (cirrhosis). You may not be able to take medication that contains acetaminophen.

FDA pregnancy category C. It is not known whether Darvocet is harmful to an unborn baby, but it could cause breathing problems or addiction/withdrawal symptoms in a newborn. Tell your doctor if you are pregnant or plan to become pregnant during treatment. Acetaminophen and propoxyphene can pass into breast milk and may harm a nursing baby. Do not use Darvocet without telling your doctor if you are breast-feeding a baby.

 


Verdicts & Settlements

Scott has been involved in numerous and diverse settlements and verdicts throughout his 18 year legal career.  He prides himself on taking care of the injured people he represents.  Scott has represented individuals from almost every state in the country and can point to settlements involving millions of dollars. Whether it be a faulty medical device, a flawed manufacturing process, a failed prescription drug or some other issue that has caused personal injury, Scott has the experience, determination and the integrity to represent a client’s interests aggressively and see that justice is served. The following examples are but a few of recent notable accomplishments:

  • Hundreds of Scott’s clients from numerous states received monetary awards in the Silicone breast implant litigation. These cases involved defective leaking or ruptured silicone implants which caused significant injury, illness and/or damage to women who relied on the manufactures of the implants.  Scott worked with the women all the way through to verdict or settlement and was responsible for ultimately settling client cases for millions of dollars.

  • Scott represented clients in the Rezulin litigation which involved a drug used by diabetics. The FDA ultimately removed the drug from the market due to liver and cardiac adverse events. Scott was involved in hundreds of hours of document review and depositions in the U.S. and Europe.  He deposed corporate witnesses who designed, manufactured, marketed and sold the drug and his clients received exceptional settlements.

  • Scott and his partner Ed Blizzard were involved in representing hundreds of individuals who suffered as a result of defective Sulzer hip and knee implant replacement joints.  Scott and Ed worked at both the state and federal level and were instrumental in developing documents and deposing corporate witnesses so that ultimately a global settlement of all claims was announced.  Scott and Ed were able to secure millions in settlement for their clients.

  • Scott represented many clients who encountered problems as a result of the diet drugs Pondimin and Redux.  He was involved with discovery committees, reviewed thousands of documents and deposed many corporate witnesses.  He tried many of these cases to verdict receiving large settlements for his clients. In December 2000, Scott tried a case in Philadelphia for two ladies from Utah who developed heart valve damage after taking the diet drug combination known as Fen-Phen. After a two week trial the jury awarded each of his clients $100 million dollars. This $200 million dollar verdict stands today as the largest Fen-Phen valvular heart disease verdict in the country. Because of this verdict, Scott was inducted into the Million Dollar and the Multi-Million Dollar Advocates Forum.

  • Scott’s clients in the Ephedra litigation were compensated well for the damages they suffered.  These cases involved  products such as Herbalife, Dexatrim, Stacker and Hydroxicut that were associated with heart attacks and strokes. He was heavily involved in developing justification documents and taking corporate depositions that ultimately led to large dollar settlements for his clients.  

Most recently, Scott began working on Paxil birth defect cases. Paxil is an antidepressant still used by millions of Americans daily.  In recent years, however, it has been associated with significant heart defects when ingested by women during the first trimester of a pregnancy.  Scott has been actively prosecuting these cases against GSK, maker of the drug. One of his cases was the first to be set for trial.  The case was resolved in favor of Scott’s client.

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