Skelaxin

Generic Name: Metaxalone
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.^b

Uses for Skelaxin

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 condition^{105 106 108} ), 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

Skelaxin 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 Skelaxin

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 Skelaxin

Specific Drugs and Laboratory Tests

Skelaxin 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.

Comparative Pricing

This pricing information is subject to change at the sole discretion of DS Pharmacy. This pricing information was updated 02/2013. 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