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Medication Safety Issues
Sound-alike/look-alike issues:
Methocarbamol may be confused with mephobarbital
Robaxin® may be confused with ribavirin, Rubex®
Pronunciation
(meth oh KAR ba mole)
U.S. Brand Names
Generic Available
Yes: Tablet
Canadian Brand Names
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
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 (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: Use with caution in patients with hepatic impairment.
• Renal impairment: Use oral with caution in patients with renal impairment.
• 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:
• Pediatrics: Oral formulation: Safety and efficacy have not been established in children <16 years of age.
Dosage form specific issues:
• Injection: Rate of injection should not exceed 3 mL/minute; solution is hypertonic; avoid extravasation. Vial stopper contains latex.
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
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. Risk C: Monitor therapy
Pyridostigmine: Methocarbamol may diminish the therapeutic effect of Pyridostigmine. Risk C: Monitor therapy
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).
Storage
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
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. Avoid alcohol.
Administration: I.M.
A maximum of 5 mL can be administered into each gluteal region.
Administration: I.V.
Maximum rate: 3 mL/minute; injection should not be used for more than 3 consecutive days; may be administered undiluted
Administration: I.V. Detail
Monitor closely for extravasation. Administer I.V. while in recumbent position. Maintain position 15-30 minutes following infusion.
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.
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.
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
Assess other medications for excess CNS depression. Monitor effectiveness of therapy (according to rationale for therapy) and adverse reactions at beginning and periodically during therapy. Monitor I.V. site closely to prevent extravasation. Assess knowledge/teach patient appropriate use, interventions to reduce side effects, and adverse symptoms to report.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Injection, solution: 100 mg/mL (10 mL) [in polyethylene glycol; vial stopper contains latex]
Tablet: 500 mg, 750 mg
Pricing: U.S. (www.drugstore.com)
Tablets (Methocarbamol)
500 mg (60): $14.97
Tablets (Robaxin)
500 mg (30): $37.97
Tablets (Robaxin-750)
750 mg (30): $48.52
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
Lexi-Comp.com
Last full review/revision September 2008
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