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Metaxalone (Monograph)

Brand name: Skelaxin
Drug 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

Medically reviewed by on Feb 14, 2024. Written by ASHP.


Centrally acting skeletal muscle relaxant.

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.

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

Various skeletal muscle relaxants appear to have comparable efficacy for low back pain relief.

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

Metaxalone Dosage and Administration


Oral Administration

Administer orally.

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


Pediatric Patients

Muscular Conditions

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


Muscular Conditions

800 mg 3 or 4 times daily.

Cautions for Metaxalone




Serotonin Syndrome

Serotonin syndrome reported in patients receiving higher than recommended doses of metaxalone or concomitant therapy with serotonergic drugs. (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).

Discontinue metaxalone if serotonin syndrome is suspected.

Concomitant Use with CNS Depressants

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

Sensitivity Reactions

Hypersensitivity Reactions

Possible hypersensitivity reactions.

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.


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

Pediatric Use

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

Geriatric Use

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

Hepatic Impairment

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

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

Renal Impairment

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

Common Adverse Effects

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

Drug Interactions

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)

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

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

Serotonin syndrome reported with concomitant use

Observe patient carefully, particularly during treatment initiation or dosage adjustments

Discontinue immediately if serotonin syndrome suspected

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

Possible false-positive results

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

No interference with test

Metaxalone Pharmacokinetics



Absolute bioavailability not determined.

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


Usually within 1 hour.


About 4–6 hours.


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%.



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



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

Elimination Route

Excreted in urine as unidentified metabolites.


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







Advice to Patients


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 2024, Selected Revisions February 24, 2020. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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