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Class: Centrally Acting Skeletal Muscle Relaxants
VA Class: MS200
Chemical Name: 5-[(3,5-Dimethylphenoxy)methyl]-2-oxazolidinone
Molecular Formula: C12H15NO3
CAS Number: 1665-48-1
Brands: Skelaxin

Medically reviewed by Last updated on Feb 24, 2020.


Centrally acting skeletal muscle relaxant.b

Uses for Metaxalone

Muscular Conditions

Adjunct to rest, physical therapy, analgesics, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.1 15 112

If pharmacologic therapy is required for acute low back pain (usually a benign and self-limiting condition105 106 108 ), experts state that an NSAIA or skeletal muscle relaxant may be considered.109 Skeletal muscle relaxants may provide small improvements in pain relief, but are associated with a high incidence of adverse effects (e.g., CNS effects).104 106 107 108 109 Use with caution after weighing risks against benefits.104 106 107 108

Various skeletal muscle relaxants appear to have comparable efficacy for low back pain relief.103 104 106 108

Metaxalone is ineffective in the treatment of skeletal muscle hyperactivity secondary to chronic neurologic disorders (e.g., cerebral palsy) and other dyskinesias.b

Metaxalone Dosage and Administration


Oral Administration

Administer orally.1

Manufacturer makes no specific recommendations regarding administration with meals; however, administration with food may increase exposure, which can increase sedative effects.1 (See Food under Pharmacokinetics.)


Pediatric Patients

Muscular Conditions

Children >12 years of age: 800 mg 3 or 4 times daily.1


Muscular Conditions

800 mg 3 or 4 times daily.1

Cautions for Metaxalone


  • History of drug-induced, hemolytic, or other anemia.1

  • Substantial hepatic or renal impairment.1

  • Known hypersensitivity to metaxalone or any ingredient in the formulation.1



Serotonin Syndrome

Serotonin syndrome reported in patients receiving higher than recommended doses of metaxalone or concomitant therapy with serotonergic drugs.1 (See Specific Drugs and Laboratory Tests under Interactions.)

Characterized by mental status and behavioral changes (e.g., agitation, hallucinations, coma), altered muscle tone or neuromuscular activity (e.g., hyperreflexia, incoordination, rigidity), autonomic instability (e.g., tachycardia, labile BP, hyperthermia), and GI symptoms (e.g., nausea, vomiting, diarrhea).1

Discontinue metaxalone if serotonin syndrome is suspected.1

Concomitant Use with CNS Depressants

May enhance the effects of other CNS depressants.1 (See Specific Drugs and Laboratory Tests under Interactions.)

Sensitivity Reactions

Hypersensitivity Reactions

Possible hypersensitivity reactions.b

Specific Populations


Animal studies have failed to reveal fetal risk, but safe use during pregnancy not established; do not use in women who are or may become pregnant unless possible benefits outweigh potential risks.1


Not known whether metaxalone is distributed into milk.1 Use not recommended.1

Pediatric Use

Safety and efficacy not established in children ≤12 years of age.1

Geriatric Use

Because of risk of injury, skeletal muscle relaxants should generally be avoided in geriatric patients.111

Hepatic Impairment

Use with caution; contraindicated in patients with substantial hepatic impairment.1

Perform liver function tests periodically in patients with preexisting liver damage.1

Renal Impairment

Use with caution; contraindicated in patients with substantial renal impairment.1

Common Adverse Effects

Drowsiness, dizziness, headache, nervousness or irritability, nausea, vomiting, GI upset.1 b

Interactions for Metaxalone

Specific Drugs and Laboratory Tests

Drug or Test



CNS depressants (e.g., alcohol, benzodiazepines, opiate agonists, tricyclic antidepressants)

Additive CNS depression; fatalities reported following inadvertent or intentional overdosage of metaxalone when used in conjunction with other CNS depressants (e.g., alcohol, antidepressants)1

Use concomitantly with caution and monitor patients closely for respiratory depression and sedation1

Serotonergic drugs (e.g., SSRIs, SNRIs, tricyclic antidepressants, meperidine, MAO inhibitors, tramadol)

Serotonin syndrome reported with concomitant use1

Observe patient carefully, particularly during treatment initiation or dosage adjustments1

Discontinue immediately if serotonin syndrome suspected1

Tests for glucose that utilize cupric sulfate (Benedict’s Solution, Clinitest, Fehling’s Solution)

Possible false-positive results1 b

Tests for glucose that utilize glucose oxidase (Clinistix, Diastix, Tes-Tape)

No interference with test1 b

Metaxalone Pharmacokinetics



Absolute bioavailability not determined.1

Bioavailability appears to increase with age under fasted, but not fed, conditions.1 Bioavailability is higher and mean half-life is longer in females compared with males.1


Usually within 1 hour.b


About 4–6 hours.b


High-fat meal delays time to peak plasma concentration by about 1–2 hours, increases peak plasma concentration by 178–194%, and increases extent of absorption (AUC) by 115–142%.1



Not known whether metaxalone crosses the placenta or is distributed into milk.1 b



Metabolized in the liver by CYP1A2, 2D6, 2E1, 3A4, and to a lesser extent, by CYP2C8, 2C9, and 2C19.1

Elimination Route

Excreted in urine as unidentified metabolites.1


About 2–4 hours under fed conditions; about 8–9 hours under fasted conditions.1







  • CNS depressant with sedative and skeletal muscle relaxant effects.1 b

  • Precise mechanism of action is not known; does not directly relax skeletal muscle and has minimal skeletal muscle relaxant effect.1 b Beneficial effect probably is related to sedative properties.1 b

  • Unlike neuromuscular blocking agents, does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.b

Advice to Patients

  • Potential for metaxalone to impair mental alertness or physical coordination, especially with concomitant use of alcohol or other CNS depressants; use caution when driving or operating machinery.1

  • Risk of serotonin syndrome with higher than recommended doses or concomitant therapy with serotonergic drugs.1 Advise patients of the symptoms of serotonin syndrome and instruct them to seek immediate medical care if they develop any such symptoms.1

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription (e.g., serotonergic drugs) and OTC drugs and dietary or herbal supplements, as well as concomitant illnesses.1

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.1

  • Importance of informing patients of other important precautionary information.1 (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name



Dosage Forms


Brand Names




800 mg*

Metaxalone Tablets

Skelaxin (scored)


AHFS DI Essentials™. © Copyright 2020, Selected Revisions February 24, 2020. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.


Only references cited for selected revisions after 1984 are available electronically.

1. Pfizer. Skelaxin (metaxalone) tablets prescribing information. NY, NY; 2018 Mar.

15. SCHWAB RS. MUSCLE RELAXANTS. Practitioner. 1964; 192:104-8.

103. See S, Ginzburg R. Skeletal muscle relaxants. Pharmacotherapy. 2008; 28:207-13.

104. van Tulder MW, Touray T, Furlan AD et al. Muscle relaxants for non-specific low back pain. Cochrane Database Syst Rev. 2003; :CD004252.

105. Roelofs PD, Deyo RA, Koes BW et al. Non-steroidal anti-inflammatory drugs for low back pain. Cochrane Database Syst Rev. 2008; :CD000396.

106. Chou R, Qaseem A, Snow V et al. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med. 2007; 147:478-91.

107. Institute for Clinical Systems Improvement. Health care guideline: adult acute and subacute low back pain. 15th ed. Bloomington, MN; 2012 Jan. From the ICSI website

108. Toth PP, Urtis J. Commonly used muscle relaxant therapies for acute low back pain: a review of carisoprodol, cyclobenzaprine hydrochloride, and metaxalone. Clin Ther. 2004; 26:1355-67.

109. Qaseem A, Wilt TJ, McLean RM et al. Noninvasive Treatments for Acute, Subacute, and Chronic Low Back Pain: A Clinical Practice Guideline From the American College of Physicians. Ann Intern Med. 2017; 166:514-530.

110. Friedman BW, Cisewski D, Irizarry E et al. A Randomized, Double-Blind, Placebo-Controlled Trial of Naproxen With or Without Orphenadrine or Methocarbamol for Acute Low Back Pain. Ann Emerg Med. 2018; 71:348-356.e5.

111. Spence MM, Shin PJ, Lee EA et al. Risk of injury associated with skeletal muscle relaxant use in older adults. Ann Pharmacother. 2013 Jul-Aug; 47:993-8.

112. Friedman BW, Irizarry E, Solorzano C et al. A Randomized, Placebo-Controlled Trial of Ibuprofen Plus Metaxalone, Tizanidine, or Baclofen for Acute Low Back Pain. Ann Emerg Med. 2019;

113. Friedman BW, Dym AA, Davitt M et al. Naproxen With Cyclobenzaprine, Oxycodone/Acetaminophen, or Placebo for Treating Acute Low Back Pain: A Randomized Clinical Trial. JAMA. 2015; 314:1572-80.

b. AHFS Drug Information 2020. Snow EK, ed. Metaxalone. Bethesda, MD: American Society of Health-System Pharmacists; 2020.