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VIRTUS PHARMACE
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69543013450

methocarbamol 500 mg tablet

Generic
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Uses

Muscular Conditions

Methocarbamol is used as an adjunct to rest, physical therapy, analgesics, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. Skeletal muscle relaxants generally appear to be more effective than placebo in providing symptomatic relief of acute low back pain, but are associated with a high incidence of adverse effects. Although comparative studies are limited, available data suggest that various skeletal muscle relaxants generally have similar efficacy for such use. Acute low back pain usually is a benign and self-limiting condition that improves spontaneously over time; if pharmacologic therapy is required, an analgesic agent such as acetaminophen or a nonsteroidal anti-inflammatory agent (NSAIA) generally is recommended as first-line therapy for most patients. Skeletal muscle relaxants (alone or in combination with analgesics) may be used as an option for short-term relief of acute low back pain; however, the possibility of adverse effects, particularly adverse CNS effects, should be considered. In general, skeletal muscle relaxants should be used with caution after weighing the potential risks against the benefits in individual patients.

Well-controlled clinical studies have not conclusively demonstrated whether relief of musculoskeletal pain by methocarbamol results from skeletal muscle relaxant effects, sedative effects, or a placebo effect of the drug. Most authorities attribute the beneficial effects of methocarbamol to its sedative properties. The drug is ineffective in the treatment of skeletal muscle hyperactivity secondary to chronic neurologic disorders, such as cerebral palsy, and other dyskinesias.

Tetanus

Methocarbamol has been used as an adjunct to debridement, tetanus antitoxin, penicillin, tracheotomy, fluid and electrolyte replacement, and supportive therapy in the management of tetanus. However, most authorities prefer administration of diazepam, meprobamate, barbiturates, or chlorpromazine, and in severe cases, administration of neuromuscular blocking agents.

Seizure Disorders

Although some clinicians have used IV or IM methocarbamol to terminate epileptic seizures, the drug may precipitate seizures. (See Cautions: Adverse Effects.)

Dosage and Administration

Administration

Methocarbamol is usually administered orally. When oral methocarbamol therapy is not feasible or in patients with severe musculoskeletal pain, the drug may be given IM or IV. Methocarbamol should not be administered subcutaneously.

The patient should be recumbent during and for 10-15 minutes following IV administration of methocarbamol, and direct IV injections should be made slowly to minimize adverse effects.

For IV administration, methocarbamol may be administered undiluted directly into the vein at a maximum rate of 300 mg (3 mL of 10% injection) per minute. For IV infusion, 1 g of methocarbamol may be diluted with up to 250 mL of 5% dextrose or 0.9% sodium chloride injection. Extravasation should be avoided, since the injection is hypertonic. (See Cautions: Adverse Effects.) Blood does not mix with methocarbamol injection, and blood in the syringe can either be injected with the drug or the injection of methocarbamol can be stopped when the plunger reaches the blood.

For IM administration, not more than 500 mg (5 mL of 10% methocarbamol injection) should be given into each gluteal region.

Dosage

Dosage of methocarbamol must be carefully adjusted according to individual requirements and response.

Muscular Conditions

The usual initial adult oral dosage of methocarbamol is 1.5 g 4 times daily for 2-3 days. In a few patients, 8 g daily in divided doses may be required initially. For maintenance therapy, the initial dosage can be decreased to 4-4.5 g daily in 3-6 divided doses.

The usual adult IM or IV dose of methocarbamol is 1 g. Generally, oral therapy with the drug can be initiated after one injection to maintain relief of musculoskeletal pain. For more severe conditions or when oral administration is not feasible, additional IM or IV doses may be administered at 8-hour intervals. Total adult IV or IM dosage should not exceed 3 g daily for 3 consecutive days, except in the treatment of tetanus. If necessary, the drug may be readministered IM or IV after a drug-free interval of 2 days. Oral administration of methocarbamol should replace parenteral administration as soon as possible.

Tetanus

Adult Dosage

When methocarbamol is used in the management of tetanus, the usual initial adult dosage is 1-2 g by direct IV injection, administered at a rate of 300 mg/minute. An additional 1- to 2-g dose may be administered by IV infusion so that a total initial dosage of up to 3 g is given. IV infusion of 1-2 g should be repeated every 6 hours until a nasogastric tube can be inserted. Methocarbamol tablets may then be crushed and suspended in water or saline solutions and administered through the nasogastric tube. Total adult oral dosage of up to 24 g daily may be required for the management of tetanus.

Pediatric Dosage

For the management of tetanus in children, the recommended minimum initial IV dose of methocarbamol is 15 mg/kg or 500 mg/m. This dose is repeated every 6 hours, if necessary. Maintenance dosage can be given by direct IV injection or as an IV infusion. In children, some clinicians have suggested that the drug be injected at a rate of 180 mg/m per minute and that total dosage should not exceed 1.8 g/m daily for 3 consecutive days.

Cautions

Adverse Effects

The most frequent adverse effects of methocarbamol are drowsiness, dizziness, and lightheadedness. Blurred vision, headache, fever, and nausea may occur after oral, IM, or IV administration of the drug. Anorexia has been reported after oral administration. Adynamic ileus occurred in one patient who received a total of 10 g of methocarbamol orally. Metallic taste, GI upset, nystagmus, diplopia, flushing, vertigo, mild muscular incoordination, syncope, hypotension, and bradycardia have occurred in patients receiving the drug IM or IV.

Allergic reactions such as urticaria, pruritus, rash, skin eruptions, and conjunctivitis with nasal congestion may occur in patients receiving methocarbamol. Anaphylactic reactions have occurred following IM or IV administration of the drug. Although most patients with methocarbamol-induced syncope recover with supportive treatment, epinephrine, corticosteroids, and/or antihistamines have been used to increase the rate of recovery in some of these patients.

When methocarbamol is administered IV, thrombophlebitis, sloughing, and pain at the injection site may result from extravasation. IM injection of the drug may also cause local irritation. IV injection of methocarbamol may cause a small amount of hemolysis and increased hemoglobin and red blood cells in the urine. Leukopenia may occur rarely.

Although a causal relationship has not been established, seizures have been reported during IV administration of methocarbamol.

Precautions and Contraindications

Patients should be warned that methocarbamol may impair their ability to perform hazardous activities requiring mental alertness or physical coordination such as operating machinery or driving a motor vehicle. Methocarbamol should be given IV or IM with caution, if at all, to patients with known or suspected epilepsy.

Methocarbamol injection should not be administered to patients with impaired renal function because the polyethylene glycol vehicle may be irritating to the kidneys. Methocarbamol is contraindicated in patients with a previous hypersensitivity reaction to the drug.

Pediatric Precautions

Safety and efficacy of methocarbamol (other than in the management of tetanus) in children younger than 12 years of age have not been established; therefore, the drug should not be administered to children in this age group.

Pregnancy and Lactation

Pregnancy

Although there are no adequate and controlled studies to date in humans, methocarbamol produced a slight decrease in conception rate and pup survival during lactation when given orally to rats at approximately 7 times the maximum human oral dose. Methocarbamol should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.

Lactation

Since it is not known if methocarbamol is distributed into milk, the drug should be used with caution in nursing women.

Drug Interactions

CNS Depressants

Additive CNS depression may occur when methocarbamol is administered concomitantly with other CNS depressants, including alcohol. If methocarbamol is used concomitantly with other depressant drugs, caution should be used to avoid overdosage.

Other Drugs

One patient with myasthenia gravis controlled by pyridostigmine experienced severe weakness after taking methocarbamol; therefore, methocarbamol should be used with caution in patients with myasthenia gravis receiving anticholinesterase agents.

Pharmacokinetics

Absorption

Methocarbamol is rapidly and almost completely absorbed from the GI tract. Blood or serum concentrations of methocarbamol required for sedative, skeletal muscle relaxant, or toxic effects are not known. Following oral administration of a single dose of methocarbamol, peak blood or serum concentrations of the drug appear to be attained in approximately 1-2 hours; the onset of action is usually within 30 minutes. Data from an unpublished study indicate that peak blood concentrations (measured as total carbamates and expressed in terms of methocarbamol) average 16.5 mcg/mL following a single 2-g oral dose, while data from a published study (using an assay relatively specific for methocarbamol) indicate that peak serum concentrations average 29.8 mcg/mL following the same dose. Data from the unpublished study also indicate that after IV administration of 1 g of methocarbamol at a rate of 300 mg/minute, blood concentrations of 19 mcg/mL are attained immediately and that the onset of action is almost immediate.

Distribution

In dogs, methocarbamol is widely distributed, with highest concentrations attained in the kidney and liver; lower concentrations are attained in the lungs, brain, and spleen, and low concentrations are attained in heart and skeletal muscle. The drug and/or its metabolites cross the placenta in dogs. It is not known if methocarbamol is distributed into milk in humans.

Elimination

Methocarbamol has a serum half-life of 0.9-1.8 hours. Methocarbamol is extensively metabolized, presumably in the liver, by dealkylation and hydroxylation. The drug and its metabolites are excreted rapidly and almost completely in urine. Based on limited data, about 10-15% of a single oral dose is excreted in urine as unchanged drug, about 40-50% as the glucuronide and sulfate conjugates of 3-(2-hydroxyphenoxy)-1,2-propanediol-1-carbamate and 3-(4-hydroxy-2-methoxyphenoxy)-1,2-propanediol-1-carbamate, and the remainder as unidentified metabolites. Following oral administration of radiolabeled methocarbamol in healthy individuals, very small amounts of radioactivity were excreted in feces.

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