Adult: As adjunct to rest, physical therapy or other measures for symptomatic relief of pain: As 400 mg or 800 mg tab: 800 mg 3-4 times daily. As 640 mg tab: 640 mg 3-4 times daily. Max: 2,560 mg daily. Refer to individual product guidelines for detailed recommendations when switching between the use of 400 mg or 800 mg tab to the 640 mg tab. Child: ≥13 years As 400 mg or 800 mg tab: Same as adult dose.
Renal Impairment
Severe: Contraindicated.
Hepatic Impairment
Severe: Contraindicated.
Administration
Metaxalone May be taken with or without food.
Contraindications
Known tendency for haemolytic anaemia, drug-induced anaemia, or other anaemias. Severe renal and hepatic impairment.
Special Precautions
The 400 mg or 800 mg tabs are not interchangeable with the 640 mg tab on a mg-per-mg basis due to different pharmacokinetic profiles. Mild to moderate renal and hepatic impairment. Avoid use in elderly patients. Pregnancy and lactation. Concomitant use with serotonergic agents (e.g. SNRIs, SSRIs, TCAs, MAOIs, triptans, 5-hydroxytryptamine 3 [5-HT3] receptor antagonists).
Adverse Reactions
Significant: CNS depression. Blood and lymphatic system disorders: Haemolytic anaemia, leucopenia. Gastrointestinal disorders: Nausea, vomiting, gastrointestinal distress. Hepatobiliary disorders: Jaundice. Immune system disorders: Hypersensitivity reaction, anaphylaxis. Rarely, anaphylactoid reaction. Nervous system disorders: Dizziness, headache, drowsiness, nervousness, irritability. Skin and subcutaneous tissue disorders: Rash (with or without pruritus). Potentially Fatal: Serotonin syndrome, particularly when used with other serotonergic agents (e.g. SNRIs, SSRIs, TCAs, MAOIs, triptans, 5-HT3 receptor antagonists) or when used at higher than recommended doses.
Patient Counseling Information
This medicine may cause drowsiness or dizziness, if affected, do not drive or operate machinery.
Overdosage
Symptom: Serotonin syndrome.
Management: Symptomatic and supportive treatment. Perform gastric lavage.
Drug Interactions
Increased risk of serotonin syndrome with other serotonergic agents (e.g. SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, MAOIs). Enhanced sedative effects with benzodiazepines.
Food Interaction
Enhanced CNS depressant effect with alcohol.
Lab Interference
May cause false-positive results for glucose determinations using cupric sulfate (e.g. Benedict's solution, Fehling's solution).
Action
Description: Mechanism of Action: Metaxalone is a centrally acting muscle relaxant. The precise mechanism of action has not been established. Its effect may be associated with CNS depression. It has no direct effect on the contractile mechanism of striated muscle, the motor end plate or the nerve fibre. Onset: Within 1 hour. Duration: 4-6 hours. Pharmacokinetics: Absorption: Absorbed from the gastrointestinal tract. Bioavailability: May be increased with food. Time to peak plasma concentration: Approx 3 hours. Distribution: Extensively distributed in the tissues. Volume of distribution: Approx 800 L. Metabolism: Metabolised in the liver by CYP1A2, CYP2D6, CYP2E1, CYP3A4 and to a lesser extent by CYP2C8, CYP2C9, and CYP2C19. Excretion: Via urine (as metabolites). Elimination half-life: 9±4.8 hours.
Chemical Structure
Metaxalone Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 15459, Metaxalone. https://pubchem.ncbi.nlm.nih.gov/compound/Metaxalone. Accessed Feb. 24, 2026.
Brayfield A, Cadart C (eds). Metaxalone. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 09/02/2026.Metaxalone 640 mg Tablet (INA Pharmaceutics Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 19/02/2026.Metaxalone Tablet (Actavis Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 09/02/2026.Metaxalone. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 09/02/2026.Metaxalone. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 09/02/2026.Skelaxin (Pfizer Laboratories Div Pfizer Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 18/02/2021.
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