Darvocet A500 Side Effects
Generic name: acetaminophen / propoxyphene
Note: This document contains side effect information about acetaminophen / propoxyphene. Some of the dosage forms listed on this page may not apply to the brand name Darvocet A500.
Some side effects of Darvocet A500 may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.
For the Consumer
Applies to acetaminophen / propoxyphene: oral tablet
Get emergency medical help if you have any of these signs of an allergic reaction while taking acetaminophen / propoxyphene: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have a serious side effect such as:
shallow breathing, slow heartbeat, feeling like you might pass out;
chest pain, feeling short of breath;
confusion, unusual thoughts or behavior;
seizure (convulsions); or
nausea, stomach pain, loss of appetite, itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Less serious side effects include:
feeling dizzy or drowsy;
mild nausea, vomiting, upset stomach, constipation;
headache, blurred vision; or
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.
For Healthcare Professionals
Applies to acetaminophen / propoxyphene: oral tablet
Nervous system side effects of propoxyphene have included dizziness, sedation, stupor, delirium, somnolence, ataxia, coma, syncope, and respiratory depression. The sedative effects of propoxyphene have been associated with a 60% increased risk of hip fracture in elderly patients.
Other side effects including propoxyphene dependence have been reported (although the abuse liability of propoxyphene is less than that of some other narcotic analgesics). Withdrawal symptoms (after either abrupt cessation or fast tapering) have been reported to include agitation, restlessness, anxiety, insomnia, tremor, tachycardia, hallucinations, psychosis, abdominal cramps, vomiting, sweating, and seizures.
Drug toxicity, multiple drug overdose, and narcotic overdose have also been reported with propoxyphene.
Sensorineural deafness has been reported following chronic abuse and/or large doses of propoxyphene-containing compounds. Optic atrophy has been reported following overdose.
Gastrointestinal side effects of acetaminophen are rare, except in alcoholics and after overdose. Cases of acute pancreatitis have been reported rarely with acetaminophen use. Nausea, vomiting, and constipation are relatively common effects of propoxyphene. Gastrointestinal bleeding and acute pancreatitis have also been reported with the use of propoxyphene.
One study has suggested that acetaminophen may precipitate acute biliary pain and cholestasis. The mechanism of this effect may be related to inhibition of prostaglandin and alterations in the regulation of the sphincter of Oddi.
Elevated liver function tests, jaundice and hepatotoxicity have been reported in association with propoxyphene.
A case of ischemic colitis has been reported following an overdose of propoxyphene which was complicated by severe hypotension.
Cardiovascular side effects of propoxyphene have included arrhythmia, bradycardia, cardiac/respiratory arrest, congestive arrest, congestive heart failure (CHF), tachycardia, myocardial infarction (MI), hypotension, decreased blood pressure, elevated heart rate, abnormal heart rate, and dizziness. A variety of arrhythmias (including heart block) have been reported most often in association with overdose.
Some of the cardiotoxic effects reported in association with propoxyphene may be attributable to its major active metabolite, norpropoxyphene.
Renal side effects of acetaminophen have been rare and have included acute tubular necrosis and interstitial nephritis. Cases of severe hypoglycemia have been reported in patients with chronic renal failure who received propoxyphene.
Acute tubular necrosis associated with acetaminophen usually occurs in conjunction with liver failure, but has been observed as an isolated finding in rare cases. Adverse acetaminophen renal effects are most often observed after overdose, after chronic abuse (often with multiple analgesics), or in association with acetaminophen-related hepatotoxicity. A possible increase in the risk of renal cell carcinoma has been associated with chronic acetaminophen use as well.
A single case of nephrogenic diabetes insipidus has been reported following overdose of propoxyphene (however, other causes of diabetes insipidus in that patient were not rigorously excluded).
The adverse effects of propoxyphene may be more likely and more severe in patients with renal insufficiency.
Hypersensitivity side effects to acetaminophen have been reported rarely.
Hypersensitivity side effects to propoxyphene have also been reported.
Genitourinary side effects have included a case of retroperitoneal fibrosis in association with propoxyphene therapy.
Hematologic side effects including rare cases of thrombocytopenia associated with acetaminophen have been reported. Acute thrombocytopenia has also been reported as having been caused by sensitivity to acetaminophen glucuronide, the major metabolite of acetaminophen. Methemoglobinemia with resulting cyanosis has also been observed in the setting of acute overdose. Cases of hemolytic anemia, pancytopenia, and disseminated intravascular coagulation after administration (or abuse) of propoxyphene-containing compounds have been reported rarely.
General erythematous skin rashes associated with acetaminophen have been reported, but are rare. A rare case of bullous erythema associated with acetaminophen has been reported.
Dermatologic side effects including rashes have been reported in association with both propoxyphene and acetaminophen. Itch has also been reported with the use of propoxyphene.
Respiratory side effects including a case of acetaminophen-induced eosinophilic pneumonia have been reported.
Respiratory side effects including dyspnea have been reported with the use of propoxyphene.
Musculoskeletal side effects including myopathy and rhabdomyolysis have been reported after chronic oral use. Fibrous myopathy has also been reported in propoxyphene-abusing patients who administer the drug via intramuscular injection.
Hepatic side effects of acetaminophen including severe and sometimes fatal dose dependent hepatitis have been reported in alcoholic patients. Hepatotoxicity has been increased during fasting. Several cases of hepatotoxicity from chronic acetaminophen therapy at therapeutic doses have also been reported despite a lack of risk factors for toxicity.
Hepatic side effects of propoxyphene have included elevated liver function tests, jaundice, hepatic steatosis, hepatomegaly, hepatocellular injury, and hepatotoxicity.
Alcoholic patients may develop hepatotoxicity after even modest doses of acetaminophen. In healthy patients, approximately 15 grams of acetaminophen is necessary to deplete liver glutathione stores by 70% in a 70 kg person. However, hepatotoxicity has been reported following smaller doses. Glutathione concentrations may be repleted by the antidote N-acetylcysteine. One case report has suggested that hypothermia may also be beneficial in decreasing liver damage during overdose.
In a recent retrospective study of 306 patients admitted for acetaminophen overdose, 6.9% had severe liver injury but all recovered. None of the 306 patients died.
A 19-year-old female developed hepatotoxicity, reactive plasmacytosis and agranulocytosis followed by a leukemoid reaction after acute acetaminophen toxicity.
The adverse effects of acetaminophen-propoxyphene may be more likely and more severe in patients with liver disease.
In the case of metabolic acidosis, causality is uncertain as more than one drug was ingested. The case of metabolic acidosis followed the ingestion of 75 grams of acetaminophen, 1.95 grams of aspirin, and a small amount of a liquid household cleaner. The patient also had a history of seizures which the authors reported may have contributed to an increased lactate level indicative of metabolic acidosis.
Metabolic side effects including metabolic acidosis have been reported following a massive overdose of acetaminophen.
Metabolic side effects including metabolic acidosis have been reported with the use of propoxyphene. Cases of severe hypoglycemia have been reported in patients with chronic renal failure.
Ocular side effects including eye swelling and vision blurred have been reported with the use of propoxyphene.
General side effects including drug tolerance and influenza type illness have been reported with the use of propoxyphene.
Psychiatric side effects including abnormal behavior, confusional state, hallucinations, and mental status change have been reported with the use of propoxyphene.
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