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Methocarbamol - Acetaminophen - Codeine
Muscle Relaxant - Analgesic
Action And Clinical Pharmacology: The mechanism of action of methocarbamol has not been established, but may be due to general CNS depression. It has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber. Methocarbamol is metabolized to yield a dealkylated and a hydroxylated product. These 2 metabolites are found primarily as glucuronide and sulfate conjugates. Based on elimination of radioactivity, the half-life of methocarbamol and its metabolites is about 2 hours. Animal studies reveal that methocarbamol crosses the placental barrier and blood-brain barrier.

Acetaminophen is a nonopiate, nonsalicylate analgesic and antipyretic. Acetaminophen is conjugated in the liver to form glucuronide and sulfate conjugates. Its plasma half-life has been reported to be from 1 to 2 hours.

Codeine is readily absorbed from the gastrointestinal tract, and a therapeutic dose reaches peak analgesic effectiveness in about 2 hours and persists for 4 to 6 hours. Oral codeine (60 mg) given to healthy males has been shown to achieve peak blood levels of 0.016 mg/100 mL at approximately 1 hour post-dose. The codeine plasma half-life for a 60 mg oral dose is about 2.9 hours. Blood levels causing CNS depression begin at 0.05 to 0.19 mg/100 mL.

The single lethal dose of codeine in adults is estimated to be approximately 0.5 to 1.0 g. Codeine is rapidly distributed from blood to body tissues and taken up preferentially by parenchymatous organs such as liver, spleen and kidney. It passes the blood-brain barrier and is found in fetal tissue and breast milk. The drug is not bound by plasma protein nor is it accumulated in body tissues. Codeine is metabolized in the liver to morphine and norcodeine, each representing about 10% of the administered dose of codeine. About 90% of the dose is excreted within 24 hours, primarily through the kidneys. Urinary excretion products are free and glucuronide-conjugated codeine (about 70%), free and conjugated norcodeine (about 10%), free and conjugated morphine (about 10%), normorphine (under 4%) and hydrocodone (1%). The remainder of the dose appears in the feces.

Indications And Clinical Uses: Relief of acute episodes of severe pain associated with skeletal muscle spasm: acute torticollis, acute strains and sprains, acute low back pain, acute tenosynovitis, ankle sprain, fracture, trauma, acute bursitis, acute myositis, whiplash injury.

Contra-Indications: Hypersensitivity to methocarbamol, acetaminophen or codeine. tag_WarningWarnings

Manufacturers' Warnings In Clinical States: Do not exceed recommended dosage as severe liver damage due to acetaminophen toxicity may occur. Avoid alcohol.

Precautions: General: The administration of Robaxacet-8 or other narcotics may obscure the diagnosis or clinical course in patients with acute abdominal conditions. In the presence of head injury, other intracranial lesions or a pre-existing increase in intracranial pressure, the respiratory depressant effects of narcotics and their capacity to elevate cerebrospinal fluid pressure may be markedly exaggerated. Furthermore, narcotics produce adverse reactions which may obscure the clinical course of patients with head injuries.

Robaxacet-8 should be given with caution to certain patients such as the elderly or debilitated, and those with severe impairment of hepatic or renal function, hypothyroidism, Addison's disease and prostatic hypertrophy or urethral stricture.

Occupational Hazards: Robaxacet-8 may impair the mental and/or physical abilities required for the performance of potentially hazardous tasks such as driving a car or operating machinery. The patient using this drug should be cautioned accordingly.

Drug Interactions: Patients receiving other narcotic analgesics, general anesthetics, phenothiazines, tranquilizers, sedative-hypnotics or other CNS depressants (including alcohol) concomitantly with Robaxacet-8 may exhibit an additive CNS depression. When such combined therapy is contemplated, the dose of one or both agents should be reduced.

The use of MAO inhibitors or tricyclic antidepressants with codeine preparations may increase the effect of either the antidepressant or codeine. The concurrent use of anticholinergics with codeine may produce paralytic ileus.

Methocarbamol may cause a color interference in certain screening tests for 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).

Carcinogenesis, Mutagenesis: Long-term studies in animals have not been performed to evaluate carcinogenic or mutagenic potential.

Pregnancy: There are no adequate and well-controlled studies of Robaxacet-8 in pregnant women. This product should be used during pregnancy only when in the judgment of the physician the potential benefits outweigh the potential hazards.

Labor and Delivery: The effects of Robaxacet-8 on the mother and fetus, on the duration of labor and delivery, or on later growth, development and functional maturation of the child is unknown.

Lactation: It is not known whether methocarbamol or its metabolites are secreted in human milk; however, there are indications small quantities of acetaminophen and codeine have been found in breast milk.

Children: Safety and effectiveness of this product in children 12 years of age or younger have not been established.

Adverse Reactions: The most common complaints to methocarbamol are drowsiness, nausea and dizziness or lightheadedness (seen in approximately 4 to 5% of patients). The following reactions have been associated with the drug, some of them rarely; in some instances, causal relationships have not been established: headache, nasal congestion, blurred vision, rash, pruritus and urticaria.

Adverse reactions that have been associated with the use of acetaminophen include: nausea, vomiting or diarrhea. Rarely, hypersensitivity reactions have been reported, as manifested by thrombocytopenic purpura, hemolytic anemia and agranulocytosis.

The most frequently observed adverse reactions to codeine include lightheadedness, dizziness, drowsiness, nausea, vomiting, constipation and depression of respiration. Less common reactions to codeine include euphoria, dysphoria, pruritus and skin rashes.

Gastrointestinal discomfort may be minimized by taking Robaxacet-8 with food.

Drug Abuse and Dependence: Codeine can produce drug dependence of the morphine type, and therefore has the potential for being abused. Psychic dependence, physical dependence and tolerance may develop upon repeated administration of this drug, and it should be prescribed and administered with the same degree of caution appropriate to the use of other oral narcotic-containing medications.

Symptoms And Treatment Of Overdose: Symptoms: Methocarbamol: No deaths or major toxicity have been reported from overdosage with methocarbamol, administered parenterally or orally. One adult survived the deliberate ingestion of 22 to 30 g of methocarbamol without serious toxicity. Another survived 30 to 50 g. The principal symptom was drowsiness in both cases.

Acetaminophen and Codeine: Serious overdose with acetaminophen and codeine is characterized by respiratory depression (a decrease in respiratory rate and/or tidal volume; Cheyne-Stokes respiration; cyanosis), extreme somnolence progressing to stupor or coma, skeletal muscle flaccidity, cold and clammy skin, and sometimes bradycardia and hypotension. In severe overdosage, apnea, circulatory collapse, cardiac arrest and death may occur. The ingestion of very large amounts of this drug may, in addition, result in acute hepatic toxicity from acetaminophen.

Treatment: Methocarbamol: Supportive measures include maintenance of an adequate airway, monitoring urinary output and vital signs, and the administration of i.v. fluids, if necessary. There is no experience with forced diuresis or with dialysis in the treatment of methocarbamol overdosage. Likewise, the usefulness of hemodialysis in managing methocarbamol overdose is unknown.

Acetaminophen and Codeine: Primary attention should be given to reestablishment of adequate respiratory exchange through provision of a patent airway and the institution of assisted or controlled ventilation. The narcotic antagonist naloxone is a specific antidote against respiratory depression which may result from overdosage or unusual sensitivity to narcotics, including codeine. Therefore, an appropriate dose of naloxone (usual initial adult dose: 0.4 mg) should be administered, preferably by the i.v. route, and simultaneously with efforts at respiratory resuscitation. Since the duration of action of codeine may exceed that of the antagonist, the patient should be kept under continued surveillance and repeated doses of the antagonist should be administered as needed to maintain adequate respiration. An antagonist should not be administered in the absence of clinically significant respiratory or cardiovascular depression. Oxygen, i.v. fluids, vasopressors and other supportive measures should be employed as indicated. Gastric emptying may be useful in removing unabsorbed drug.

Acetaminophen in massive overdosage may cause hepatotoxicity in some patients. Clinical and laboratory evidence of hepatotoxicity may be delayed for up to 1 week. Close clinical monitoring and serial hepatic enzyme determinations are therefore recommended.

The antidote, N-acetylcysteine, should be administered as early as possible, and within 16 hours of the overdose ingestion for optimal results. Following recovery, there are no residual, structural or functional hepatic abnormalities.

Dosage: Adults: 1 or 2 tablets 3 or 4 times a day.

Availability And Storage: Each coated, blue and white caplet, blue layer engraved "WR", white layer scored, contains: methocarbamol 400 mg, acetaminophen 325 mg and codeine phosphate 8 mg. Nonmedicinal ingredients: calcium sulfate, cellulose, cornstarch, FD&C Blue No. 1, magnesium stearate, polyethylene glycol, povidone, sodium lauryl sulfate, sodium starch glycolate and stearic acid. Energy: <1 kJ (<1 kcal). Sodium: <1 mmol (0.9 mg). Bottles of 100. Boxes of 18.