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Pronunciation
(me TAKS a lone)
Generic Available (U.S.)
Yes
U.S. Brand Names
Canadian Brand Names
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Relief of discomfort associated with acute, painful musculoskeletal conditions
Pregnancy Considerations
Teratogenic effects were not observed in animal studies. There are no adequate and well-controlled studies in pregnant women. Use during pregnancy (especially first trimester) only if benefits outweigh risks.
Lactation
Excretion in breast milk unknown/not recommended
Contraindications
Hypersensitivity to metaxalone or any component of the formulation; significantly impaired hepatic or renal function, history of drug-induced hemolytic anemias or other anemias
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; routine monitoring of transaminases is recommended. Contraindicated in patients with significant impairment.
• Renal impairment: Use with caution in patients with renal impairment; contraindicated in patients with significant impairment.
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).
• Females: An increase in bioavailability and half-life have been observed in female patients.
• Pediatrics: Safety and efficacy have not been established in children ≤12 years of age.
Adverse Reactions
Frequency not defined.
Central nervous system: Dizziness, drowsiness, headache, irritability, nervousness
Dermatologic: Rash (with or without pruritus)
Gastrointestinal: Gastrointestinal upset, nausea, vomiting
Hematologic: Hemolytic anemia, leukopenia
Hepatic: Jaundice
Miscellaneous: Hypersensitivity (including rare anaphylactoid reactions)
Metabolism/Transport Effects
Substrate of CYP1A2, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4
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
Conivaptan: May increase the serum concentration of CYP3A4 Substrates. Management: Upon completion/discontinuation of conivaptan, allow at least 7 days before initiating therapy with drugs that are CYP3A4 substrates. Risk D: Consider therapy modification
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. Management: For patients being treated with hydroxyzine, a reduction in the dose of any other CNS depressants that are to be used in combination is recommended. With concurrent use, monitor patients closely for excessive response to the combination. Risk D: Consider therapy modification
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
Peginterferon Alfa-2b: May decrease the serum concentration of CYP2D6 Substrates. 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
Tocilizumab: May decrease the serum concentration of CYP3A4 Substrates. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Ethanol: May increase CNS depression; monitor for increased effects with coadministration. Caution patients about effects.
Food: Bioavailability may be increased (may increase CNS depression).
Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola (may increase CNS depression).
Storage
Store at controlled room temperature of 15°C to 30°C (59°F to 86°F).
Mechanism of Action
Precise mechanism has not been established; however, efficacy appears to result from disruption of the spasm-pain-spasm cycle, probably by a general CNS depressant effect. Does not have a direct effect on skeletal muscle.
Pharmacodynamics/Kinetics
Onset of action: ~1 hour
Duration: ~4-6 hours
Distribution: Vd: ~800 L
Metabolism: Hepatic via CYP1A2, CYP2D6, CYP2E1, CYP3A4 and to lesser extent CYP2C8, CPY2C9, and CYP2C19
Bioavailability: Not established; food may increase
Half-life elimination: 4-14 hours
Time to peak: Tmax: ~3 hours
Excretion: Urine (as metabolites)
Dosage
Oral: Children >12 years and Adults: Muscle discomfort: 800 mg 3-4 times/day
Dosage adjustment in renal impairment: Use caution in patients with mild-to-moderate renal impairment; contraindicated with significant impairment. No specific recommendation are provided in approved labeling.
Dosage adjustment in hepatic impairment: Use caution in patients with mild-to-moderate hepatic impairment; contraindicated with significant impairment. No specific recommendation are provided in approved labeling.
Administration: Oral
May be administered with or without food. However, serum concentrations may be increased when administered with food; clinical significance has not been established. Patients should be monitored.
Test Interactions
False-positive Benedict's test
Dietary Considerations
Administration with food may increase serum concentrations.
Geriatric Considerations
This medication is considered to be potentially inappropriate in this patient population (Beers Criteria severity: High).
Dental Health: Effects on Dental Treatment
No significant effects or complications reported
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
Drowsiness and dizziness are common; may cause paradoxical stimulation
Mental Health: Effects on Psychiatric Treatment
May cause leukopenia; use caution with clozapine and carbamazepine; concurrent use with psychotropics may produce additive sedation
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Tablet, oral: 800 mg
Skelaxin®: 800 mg [scored]
Pricing: U.S. (www.drugstore.com)
Tablets (Metaxalone)
800 mg (30): $99.99
Tablets (Skelaxin)
800 mg (30): $128.60
References
Toth PP and Urtis J, “Commonly Used Muscle Relaxant Therapies for Acute Low Back Pain: A Review of Carisoprodol, Cyclobenzaprine Hydrochloride, and Metaxalone,” Clin Ther, 2004, 26(9):1355-67.
International Brand Names
Lexi-Comp.com
Last full review/revision May 2011
Content last modified May 2011
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