Metaxalone

Pronunciation

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

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.101 b

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

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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.101

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.)

Dosage

Pediatric Patients

Muscular Conditions
Oral

Children >12 years of age: 800 mg 3 or 4 times daily.101 b

Adults

Muscular Conditions
Oral

800 mg 3 or 4 times daily.101 b

Cautions for Metaxalone

Contraindications

  • History of drug-induced, hemolytic, or other anemia.101 b

  • Substantial hepatic or renal impairment.101 b

  • Known hypersensitivity to metaxalone or any ingredient in the formulation.101 b

Warnings/Precautions

Warnings

CNS Depressants

May enhance the effects of other CNS depressants.101 b (See Specific Drugs and Laboratory Tests under Interactions.)

Sensitivity Reactions

Hypersensitivity Reactions

Possible hypersensitivity reactions.101 b

Specific Populations

Pregnancy

Category B.

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

Lactation

Not known whether metaxalone is distributed into milk.101 Use not recommended.101 b

Pediatric Use

Safety and efficacy not established in children ≤12 years of age.101 b

Geriatric Use

Use with caution due to greater frequency of decreased hepatic or renal function and of concomitant disease and drug therapy observed in the elderly.101 b

Hepatic Impairment

Use great caution in patients with a history of liver disease.101 b Perform liver function tests periodically during metaxalone therapy.101 b

Contraindicated in patients with substantial hepatic impairment.101 b

Renal Impairment

Caution advised; contraindicated in patients with substantial renal impairment.101 b

Common Adverse Effects

Drowsiness, dizziness, headache, nervousness or irritability, nausea, vomiting, GI upset.101 b

Interactions for Metaxalone

Specific Drugs and Laboratory Tests

Drug or Test

Interaction

Comments

CNS depressants (e.g., alcohol, barbiturates)

Additive CNS depression101 b

Use caution to avoid overdosage101 b

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

Possible false-positive results101 b

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

No interference with test101 b

Metaxalone Pharmacokinetics

Absorption

Bioavailability

Absolute bioavailability not determined.101

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%; clinical importance unknown.101

Distribution

Extent

Not known whether metaxalone crosses the placenta or is distributed into milk.101 b

Elimination

Metabolism

Metabolized in the liver.101 b

Elimination Route

Excreted in urine as unidentified metabolites.101 b

Half-life

About 2–4 hours.101 b

Stability

Storage

Oral

Tablets

15–30°C.101 b

Actions

  • CNS depressant with sedative and skeletal muscle relaxant effects.101 b

  • 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 clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as concomitant illnesses.101 b

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.101 b

  • 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.

Metaxalone

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Tablets

800 mg

Skelaxin (scored)

King

Comparative Pricing

This pricing information is subject to change at the sole discretion of DS Pharmacy. This pricing information was updated 02/2014. Actual costs to patients will vary depending on the use of specific retail or mail-order locations and health insurance copays.

Metaxalone 800MG Tablets (COREPHARMA LLC): 30/$119.99 or 90/$342.97

Skelaxin 800MG Tablets (KING PHARMA): 30/$141.74 or 90/$388.46

AHFS DI Essentials. © Copyright, 2004-2014, Selected Revisions November 18, 2012. American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland 20814.

References

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. [PubMed 18225966]

104. van Tulder MW, Touray T, Furlan AD et al. Muscle relaxants for non-specific low back pain. Cochrane Database Syst Rev. 2003; :CD004252. [PubMed 12804507]

105. Roelofs PD, Deyo RA, Koes BW et al. Non-steroidal anti-inflammatory drugs for low back pain. Cochrane Database Syst Rev. 2008; :CD000396. [PubMed 18253976]

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. [PubMed 17909209]

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. [PubMed 15530999]

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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