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
Introduction
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
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.)
Dosage
Pediatric Patients
Muscular Conditions
Oral
Children >12 years of age: 800 mg 3 or 4 times daily.
Adults
Muscular Conditions
Oral
800 mg 3 or 4 times daily.
Cautions for Metaxalone
Contraindications
-
History of drug-induced, hemolytic, or other anemia.
-
Substantial hepatic or renal impairment.
-
Known hypersensitivity to metaxalone or any ingredient in the formulation.
Warnings/Precautions
Warnings
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
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.
Lactation
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 |
Interaction |
Comments |
---|---|---|
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
Absorption
Bioavailability
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.
Onset
Usually within 1 hour.
Duration
About 4–6 hours.
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%.
Distribution
Extent
Not known whether metaxalone crosses the placenta or is distributed into milk.
Elimination
Metabolism
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.
Half-life
About 2–4 hours under fed conditions; about 8–9 hours under fasted conditions.
Stability
Storage
Oral
Tablets
15–30°C.
Actions
-
CNS depressant with sedative and skeletal muscle relaxant effects.
-
Precise mechanism of action is not known; does not directly relax skeletal muscle and has minimal skeletal muscle relaxant effect. Beneficial effect probably is related to sedative properties.
-
Unlike neuromuscular blocking agents, does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.
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.
-
Risk of serotonin syndrome with higher than recommended doses or concomitant therapy with serotonergic drugs. Advise patients of the symptoms of serotonin syndrome and instruct them to seek immediate medical care if they develop any such symptoms.
-
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.
-
Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.
-
Importance of informing patients of other important precautionary information. (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
Routes |
Dosage Forms |
Strengths |
Brand Names |
Manufacturer |
---|---|---|---|---|
Oral |
Tablets |
800 mg* |
Metaxalone Tablets |
|
Skelaxin (scored) |
Pfizer |
AHFS DI Essentials™. © Copyright 2025, 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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