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standards of non-Merck sources.
Pronunciation
(meth oh KAR ba mole)
Generic Available (U.S.)
Yes: Tablet
Brand Names: U.S.
Brand Names: Canada
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Adjunctive treatment of muscle spasm associated with acute painful musculoskeletal conditions (eg, tetanus)
Use: Dental
Treatment of muscle spasm associated with acute temporomandibular joint pain (TMJ)
Pregnancy Risk Factor
C
Pregnancy Considerations
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
Concerns related to adverse effects:
• CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).
Disease-related concerns:
• Hepatic impairment: Plasma protein binding and clearance are decreased and the half-life is increased in patients with hepatic impairment.
• Renal impairment: Use of I.V. formulation is contraindicated.
• Seizure disorder: Use injection with caution in patients with a history of seizure disorder.
Concurrent drug therapy issues:
• Sedatives: Effects may be potentiated when used with other sedative drugs or ethanol.
Special populations:
• Elderly: This class of medication is poorly tolerated by the elderly due to anticholinergic effects, sedation, and weakness. Efficacy is questionable at dosages tolerated by elderly patients (Beers Criteria).
• Pediatrics: I.V. formulation: Recommended only for the treatment of tetanus in pediatric patients.
Dosage form specific issues:
• Injection: Contraindicated in renal impairment. Contains polyethylene glycol. Rate of injection should not exceed 3 mL/minute; solution is hypertonic; avoid extravasation. Vial stopper contains latex.
Adverse Reactions
Frequency not defined.
Cardiovascular: Bradycardia, flushing, hypotension, syncope
Central nervous system: Amnesia, confusion, coordination impaired (mild), dizziness, drowsiness, fever, headache, insomnia, lightheadedness, sedation, seizures, vertigo
Dermatologic: Angioneurotic edema, pruritus, rash, urticaria
Gastrointestinal: Dyspepsia, metallic taste, nausea, vomiting
Hematologic: Leukopenia
Hepatic: Jaundice
Local: Pain at injection site, thrombophlebitis
Ocular: Blurred vision, conjunctivitis, diplopia, nystagmus
Respiratory: Nasal congestion
Miscellaneous: Hypersensitivity reactions including anaphylaxis
Metabolism/Transport Effects
None known.
Drug Interactions
Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Risk C: Monitor therapy
CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Exceptions: Levocabastine (Nasal). Risk C: Monitor therapy
Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (e.g., opioids, barbiturates) with concomitant use. Risk D: Consider therapy modification
HydrOXYzine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce adult dose of CNS depressant agents by 50% with initiation of concomitant methotrimeprazine therapy. Further CNS depressant dosage adjustments should be initiated only after clinically effective methotrimeprazine dose is established. Risk D: Consider therapy modification
Pyridostigmine: Methocarbamol may diminish the therapeutic effect of Pyridostigmine. Risk C: Monitor therapy
Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Ethanol: May increase CNS depression; monitor for increased effects with coadministration. Caution patients about effects.
Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola (may increase CNS depression).
Storage
Injection: Prior to dilution, store at controlled room temperature of 20°C to 25°C (68°F to 77°F); excursions permitted to 15°C to 30°C (59°F to 86°F).
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: Oral: 1-2 hours
Excretion: Urine (primarily 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: 1-2 g by direct I.V. injection, which may be followed by an additional 1-2 g by infusion (maximum initial dose: 3 g total); followed by 1-2 g every 6 hours until oral administration by mouth or via NG tube is possible; total oral daily doses of up to 24 g may be needed; injection should not be used for more than 3 consecutive days
Muscle spasm:
Oral: Children ≥16 years and Adults: 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.: Adults: Initial: 1 g; may repeat every 8 hours if oral administration not possible; maximum dose: 3 g/day for no more than 3 consecutive days. If condition persists, may repeat course of therapy after a drug-free interval of 48 hours.
Dosing adjustment/comments in renal impairment: Administration of the parenteral formulation is contraindicated in patients with renal dysfunction due to the presence of polyethylene glycol.
Dosing adjustment in hepatic impairment: Specific dosing guidelines are not available.
Dental Usual Dosing
Muscle spasm associated with acute TMJ pain: 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
Administration: Oral
Tablets may be crushed and mixed with food or liquid if needed.
Administration: I.M.
A maximum of 5 mL can be administered into each gluteal region.
Administration: I.V.
Maximum rate: 3 mL/minute; may be administered undiluted or mixed with 5% dextrose or 0.9% saline (1 vial/≤250 mL diluent). Monitor closely for extravasation. Administer I.V. while in recumbent position. Maintain position for at least 10-15 minutes following infusion.
Monitoring Parameters
Monitor closely for extravasation (I.V. administration).
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
Do not use alcohol. You may experience drowsiness, dizziness, or lightheadedness. Report excessive drowsiness.
Geriatric Considerations
There is no specific information on the use of skeletal muscle relaxants in the elderly. Methocarbamol has a short half-life, so it may be considered one of the safer agents in this class.
This medication is considered to be potentially inappropriate in this patient population (Beers Criteria severity: High).
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
Nursing: Physical Assessment/Monitoring
Monitor I.V. site closely to prevent extravasation.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Injection, solution:
Robaxin®: 100 mg/mL (10 mL) [contains natural rubber/natural latex in packaging, polyethylene glycol 300]
Tablet, oral: 500 mg, 750 mg
Robaxin®: 500 mg [scored]
Robaxin®-750: 750 mg
Pricing: U.S. (www.drugstore.com)
Tablets (Methocarbamol)
500 mg (60): $15.99
750 mg (30): $14.99
Tablets (Robaxin)
500 mg (30): $65.40
Tablets (Robaxin-750)
750 mg (30): $82.83
International Brand Names
Lexi-Comp.com
Last full review/revision February 2012
Content last modified February 2012
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