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 Drugs.com on Feb 14, 2025. Written by ASHP.

Introduction

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 condition^{105 106 108} ), 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

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.)

Dosage

Pediatric Patients

Muscular Conditions

Oral

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

Adults

Muscular Conditions

Oral

800 mg 3 or 4 times daily.¹

Cautions for Metaxalone

Contraindications

• 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

Warnings/Precautions

Warnings

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

Pregnancy

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

Lactation

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}

Drug Interactions

Specific Drugs and Laboratory Tests

Metaxalone Pharmacokinetics

Absorption

Bioavailability

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

Onset

Usually within 1 hour.^b

Duration

About 4–6 hours.^b

Food

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

Distribution

Extent

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

Elimination

Metabolism

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

Half-life

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

Stability

Storage

Oral

Tablets

15–30°C.¹

Actions

• 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.)

Preparations

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

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