Methocarbamol

Pronunciation

(meth oh KAR ba mole)

U.S. Brand Names

Robaxin®

Generic Available

Yes: Tablet

Canadian Brand Names

Robaxin®

Use

Treatment of muscle spasm associated with acute painful musculoskeletal conditions; supportive therapy in tetanus

Use - Dental

Treatment of muscle spasm associated with acute temporomandibular joint pain

Pregnancy Risk Factor

Pregnancy Implications

Animal reproduction studies have not been conducted. The manufacturer notes that fetal and congenital abnormalities have been rarely reported following in utero exposure. Use during pregnancy only if clearly needed.

Lactation

Excretion in breast milk unknown/use caution

Contraindications

Hypersensitivity to methocarbamol or any component of the formulation; renal impairment (injection formulation)

Warnings/Precautions

Oral: Use caution with renal or hepatic impairment.

Injection: Rate of injection should not exceed 3 mL/minute; solution is hypertonic; avoid extravasation. Use with caution in patients with a history of seizures. Use caution with hepatic impairment.

Adverse Reactions

Frequency not defined.

Cardiovascular: Flushing of face, bradycardia, hypotension, syncope

Central nervous system: Drowsiness, dizziness, lightheadedness, convulsion, vertigo, headache, fever, amnesia, confusion, insomnia, sedation, coordination impaired (mild)

Dermatologic: Allergic dermatitis, urticaria, pruritus, rash, angioneurotic edema

Gastrointestinal: Nausea, vomiting, metallic taste, dyspepsia

Hematologic: Leukopenia

Hepatic: Jaundice

Local: Pain at injection site, thrombophlebitis

Ocular: Nystagmus, blurred vision, diplopia, conjunctivitis

Renal: Renal impairment

Respiratory: Nasal congestion

Miscellaneous: Allergic manifestations, anaphylactic reaction

Overdosage/Toxicology

Symptoms of overdose include cardiac arrhythmias, nausea, vomiting, drowsiness, and coma. Treatment is supportive.

Drug Interactions

Increased effect/toxicity with CNS depressants; pyridostigmine (a single case of worsening myasthenia has been reported following methocarbamol administration)

Ethanol/Nutrition/Herb Interactions

Ethanol: Avoid ethanol (may increase CNS depression).

Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola (may increase CNS depression).

Stability

Injection: Prior to dilution, store at controlled room temperature of 20°C to 25°C (68°F to 77°F). Injection when diluted to 4 mg/mL in sterile water, 5% dextrose, or 0.9% saline is stable for 6 days at room temperature; do not refrigerate after dilution

Tablet: Store at controlled room temperature of 20°C to 25°C (68°F to 77°F).

Mechanism of Action

Causes skeletal muscle relaxation by general CNS depression

Pharmacodynamics/Kinetics

Onset of action: Muscle relaxation: Oral: ~30 minutes

Protein binding: 46% to 50%

Metabolism: Hepatic via dealkylation and hydroxylation

Half-life elimination: 1-2 hours

Time to peak, serum: ~2 hours

Excretion: Urine (as metabolites)

Dosage

Tetanus: I.V.:

Children: Recommended only for use in tetanus: 15 mg/kg/dose or 500 mg/m² /dose, may repeat every 6 hours if needed; maximum dose: 1.8 g/m² /day for 3 days only

Adults: Initial dose: 1-3 g; may repeat dose every 6 hours until oral dosing is possible; injection should not be used for more than 3 consecutive days

Muscle spasm: Children 16 years and Adults:

Oral: 1.5 g 4 times/day for 2-3 days (up to 8 g/day may be given in severe conditions), then decrease to 4-4.5 g/day in 3-6 divided doses

I.M., I.V.: 1 g every 8 hours if oral not possible; injection should not be used for more than 3 consecutive days. If condition persists, may repeat course of therapy after a drug-free interval of 48 hours.

Elderly: Muscle spasm: Oral: Initial: 500 mg 4 times/day; titrate to response

Dosing adjustment/comments in renal impairment: Do not administer parenteral formulation to patients with renal dysfunction.

Dosing adjustment in hepatic impairment: Specific dosing guidelines are not available; plasma protein binding and clearance are decreased; half-life is increased

Administration

Injection:

I.M.: A maximum of 5 mL can be administered into each gluteal region.

I.V.: Maximum rate: 3 mL/minute; should not be used for more than 3 consecutive days; may be administered undiluted. Monitor closely for extravasation. Administer I.V. while in recumbent position. Maintain position 15-30 minutes following infusion.

Tablet: May be crushed and mixed with food or liquid if needed. Avoid alcohol.

Test Interactions

May cause color interference in certain screening tests for 5-HIAA using nitrosonaphthol reagent and in screening tests for urinary VMA using the Gitlow method.

Patient Education

Take exactly as directed. Do not increase dose or discontinue without consulting prescriber. Do not use alcohol, prescriptive or OTC antidepressants, sedatives, or pain medications without consulting prescriber. You may experience drowsiness, dizziness, lightheadedness (avoid driving or engaging in tasks requiring alertness until response to drug is known); or nausea or vomiting (small, frequent meals, frequent mouth care, or sucking hard candy may help). Report excessive drowsiness or mental agitation, chest pain, skin rash, swelling of mouth/face, difficulty speaking, or vision changes. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to become pregnant. Consult prescriber if breast-feeding.

Dental Health: Effects on Dental Treatment

Key adverse event(s) related to dental treatment: Metallic taste.

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

Drowsiness and dizziness are common

Mental Health: Effects on Psychiatric Treatment

May rarely cause leukopenia; use caution with clozapine and carbamazepine; concurrent use with psychotropics may produce additive sedation

Dosage Forms

Injection, solution: 100 mg/mL (10 mL) [in polyethylene glycol; vial stopper contains latex]

Tablet: 500 mg, 750 mg

References

Lebby TI, Dugger K, Lipscomb JW, et al, "Skeletal Muscle Relaxant Ingestion," Vet Hum Toxicol , 1990, 32(2):133-5.

Preston KL, Guarino JJ, Kirk WT, et al, "Evaluation of the Abuse Potential of Methocarbamol," J Pharmacol Exp Ther , 1989, 248(3):1146-57.

International Brand Names

Laxan® (TH); Lumirelax® (FR); Manobaxine® (TH); Methocarbamol® (CY, PL); Metocarbamol® (EC); Miyoreks® (TR); Musxan® (TH); Myocin® (TH); Myomethol® (IL, TH); Ortoton® (DE); Robaxin® (CA, CO, ES, GB, HK, TH, ZA); Sinaxar® (CO)

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