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 on November 20, 2017
Centrally acting skeletal muscle relaxant.b
Uses for Metaxalone
If pharmacologic therapy is required for acute low back pain (usually a benign and self-limiting condition105 106 108 ), an analgesic (e.g., acetaminophen, NSAIA) generally is recommended.104 105 106 108 117 Skeletal muscle relaxants may be used alone or in combination with analgesics for short-term relief; however, consider high incidence of adverse effects (e.g., CNS effects).104 106 107 108 Use skeletal muscle relaxants with caution and weigh risks against benefits.104 106 107 108
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
Manufacturer makes no specific recommendations regarding administration with meals; administration with high-fat meal increases absorption, but clinical importance is unknown.101 (See Food under Pharmacokinetics.)
Cautions for Metaxalone
Animal studies have failed to reveal fetal risk, but safe use during pregnancy has not been established; do not use in women who are or may become pregnant unless possible benefits outweigh potential risks.101 b
Common Adverse Effects
Interactions for Metaxalone
Specific Drugs and Laboratory Tests
Drug or Test
CNS depressants (e.g., alcohol, barbiturates)
Tests for glucose that utilize cupric sulfate (Benedict’s Solution, Clinitest, Fehling’s Solution)
Tests for glucose that utilize glucose oxidase (Clinistix, Diastix, Tes-Tape
Absolute bioavailability not determined.101
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%; clinical importance unknown.101
Precise mechanism of action is not known; does not directly relax skeletal muscle and has minimal skeletal muscle relaxant effect.101 b Beneficial effect probably is related to sedative properties.101 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.101 b
Importance of informing patients of other important precautionary information. (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.
AHFS DI Essentials. © Copyright 2018, Selected Revisions November 18, 2012. 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.
101. King Pharmaceuticals, Inc. Skelaxin (metaxalone) tablets prescribing information. Bristol, TN; 2003 Aug.
103. See S, Ginzburg R. Skeletal muscle relaxants. Pharmacotherapy. 2008; 28:207-13. http://www.ncbi.nlm.nih.gov/pubmed/18225966?dopt=AbstractPlus
104. van Tulder MW, Touray T, Furlan AD et al. Muscle relaxants for non-specific low back pain. Cochrane Database Syst Rev. 2003; :CD004252. http://www.ncbi.nlm.nih.gov/pubmed/12804507?dopt=AbstractPlus
105. Roelofs PD, Deyo RA, Koes BW et al. Non-steroidal anti-inflammatory drugs for low back pain. Cochrane Database Syst Rev. 2008; :CD000396. http://www.ncbi.nlm.nih.gov/pubmed/18253976?dopt=AbstractPlus
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. http://www.ncbi.nlm.nih.gov/pubmed/17909209?dopt=AbstractPlus
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 http://www.icsi.org/low_back_pain/adult_low_back_pain__8.html
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. http://www.ncbi.nlm.nih.gov/pubmed/15530999?dopt=AbstractPlus
117. Boothby LA, Doering PL, Hatton RC. Carisoprodol: a marginally effective skeletal muscle relaxant with serious abuse potential. Hosp Pharm. 2003; 38:337-45.
b. AHFS Drug Information 2006. McEvoy GK, ed. Metaxalone. Bethesda, MD: American Society of Health-System Pharmacists; 2006: 1391-2.
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