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Pronunciation
(me TAKS a lone)
Generic Available (U.S.)
Yes
Brand Names: U.S.
Brand Names: Canada
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 (minor), CYP2C19 (minor), CYP2C8 (minor), CYP2C9 (minor), CYP2D6 (minor), CYP2E1 (minor), CYP3A4 (minor); Note: Assignment of Major/Minor substrate status based on clinically relevant drug interaction potential
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 (Low risk). Risk C: Monitor therapy
Cyproterone: May decrease the serum concentration of CYP1A2 Substrates. Risk C: Monitor therapy
Cyproterone: May decrease the serum concentration of CYP2E1 Substrates. 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
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 January 2012
Content last modified January 2012
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