Metaxalone – LiverTox – NCBI Bookshelf

Last Update: September 13, 2021.

OVERVIEW

Introduction

Metaxalone is a centrally acting skeletal muscle relaxant that has been in use for more than 40 years. Metaxalone has not been associated with serum aminotransferase elevations during therapy or with clinically apparent hepatic injury.

Background

Metaxalone (me tax’ a lone) acts centrally as a skeletal muscle relaxant, but its efficacy and precise mechanism of action are not well documented. Metaxalone was approved for use in the United States in 1962 and has been a widely used muscle relaxant, but its use recently has declined. Current indications include the treatment of pain from acute musculoskeletal conditions and muscle spasms. The recommended dosage is 800 mg orally three to four times daily. Metaxalone is available by prescription only in 400 and 800 mg tablets in generic forms as well as under the commercial name Skelaxin. Sparse data are available regarding metaxalone safety. Side effects are not common, but can include drowsiness, dizziness, headache, nausea, and dry mouth. When combined with other serotonergic medications (such as serotonin reuptake inhibitors, tricyclic antidepressants, triptans, opiates and others), metaxalone can cause acute serotonin syndrome marked by agitation, confusion, hallucinations, tachycardia, hyperthermia, incoordination, neuromuscular rigidity, nausea and abdominal pain.

Hepatotoxicity

According to the product brochure, metaxalone may cause jaundice, although there are no specific case reports of hepatotoxicity from metaxalone in the literature and no prospective trials with routine monitoring of aminotransferase levels. Given its long history, metaxalone appears to be without significant hepatotoxicity.

Likelihood score: E (Unlikely cause of clinically apparent liver injury).

Drug Class: Muscle Relaxants

CHEMICAL FORMULA AND STRUCTURE

ANNOTATED BIBLIOGRAPHY

References updated: 13 September 2021

• Zimmerman HJ. Muscle spasmolytics. In, Hepatotoxicity: The Adverse Effects of Drugs and Other Chemicals on the Liver. 2nd Ed. Philadelphia: Lippincott, 1999. p. 544-45.

  (Expert review of hepatotoxicity published in 1999; dantrolene, chlorzoxazone and baclofen are discussed; mentions that metaxalone has been cited as causing jaundice but that no such case reports have appeared in the literature).

• Hibbs RE, Zambon AC. Agents acting at the neuromuscular junction and autonomic ganglia. In, Brunton LL, Chabner BA, Knollman BC, eds. Goodman & Gilman’s The pharmacological basis of therapeutics, 12th ed. New York: McGraw-Hill, 2011. p. 255-76.

  (Textbook of pharmacology and therapeutics)

• 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]

  (A review of safety and efficacy of muscle relaxants which states “Although rare instances of hepatic enzyme elevation and anemia have been reported [with metaxalone], this association appears to be based on a false-positive hepatic assay using the cephalin flocculation test.”).

• Chou R, Peterson K, Helfand M. Comparative efficacy and safety of skeletal muscle relaxants for spasticity and musculoskeletal conditions: a systematic review. J Pain Symptom Manage. 2004;28:140–75. [PubMed: 15276195]

  (Thorough review of the pharmacology, efficacy and side effects of the muscle relaxants).

• Moore KA, Levine B, Fowler D. A fatality involving metaxalone. Forensic Sci Int. 2005;149:249–51. [PubMed: 15749367]

  (54 year old woman found dead in whom postmortem analysis indicated metaxalone overdose; liver reported as being normal).

• Poklis JL, Ropero-Miller JD, Garside D, Winecker RE. Metaxalone (Skelaxin)-related death. J Anal Toxicol. 2004;28:537–41. [PubMed: 15516312]

  (21 year old woman found dead in whom postmortem analysis indicated metaxalone overdose; no mention of liver abnormalities, although highest levels of drug were present in liver).

• Russo MW, Galanko JA, Shrestha R, Fried MW, Watkins P. Liver transplantation for acute liver failure from drug-induced liver injury in the United States. Liver Transpl. 2004;10:1018–23. [PubMed: 15390328]

  (Among ~50,000 liver transplants done in the US between 1990 and 2002, 270 [0.5%] were done for drug induced acute liver failure, but none were attributed to muscle relaxants).

• Chalasani N, Fontana RJ, Bonkovsky HL, Watkins PB, Davern T, Serrano J, Yang H, Rochon J. , Drug Induced Liver Injury Network (DILIN). Causes, clinical features, and outcomes from a prospective study of drug-induced liver injury in the United States. Gastroenterology. 2008;135:1924–34. [PMC free article: PMC3654244] [PubMed: 18955056]

  (Among 300 cases of drug induced liver disease in the US collected from 2004 to 2008, one was attributed to chlorzoxazone, but none to metaxalone).

• Reuben A, Koch DG, Lee WM., Acute Liver Failure Study Group. Drug-induced acute liver failure: results of a U.S. multicenter, prospective study. Hepatology. 2010;52:2065–76. [PMC free article: PMC3992250] [PubMed: 20949552]

  (Among 1198 patients with acute liver failure enrolled in a US prospective study between 1998 and 2007, 133 were attributed to drug induced liver injury, but none were due to metaxalone or other muscle relaxants).

• Björnsson ES, Bergmann OM, Björnsson HK, Kvaran RB, Olafsson S. Incidence, presentation and outcomes in patients with drug-induced liver injury in the General population of Iceland. Gastroenterology. 2013;144:1419–25. [PubMed: 23419359]

  (In a population based study of drug induced liver injury from Iceland, 96 cases were identified over a 2 year period, but none were attributed to metaxalone or other muscle relaxants).

• Chalasani N, Bonkovsky HL, Fontana R, Lee W, Stolz A, Talwalkar J, Reddy KR, et al. United States Drug Induced Liver Injury Network. Features and outcomes of 899 patients with drug-induced liver injury: The DILIN Prospective Study. Gastroenterology. 2015;148:1340–1352. [PMC free article: PMC4446235] [PubMed: 25754159]

  (Among 899 cases of drug induced liver injury enrolled in a US prospective study between 2004 and 2013, 5 [0.7%] were attributed to muscle relaxants, one of which was possibly related to metaxalone).

• Li Y, Delcher C, Reisfield GM, Wei YJ, Brown JD, Winterstein AG. Utilization patterns of skeletal muscle relaxants among commercially insured adults in the United States from 2006 to 2018. Pain Med. 2021:pnab088. Epub ahead of print. [PubMed: 33690860]

  (Analysis of utilization of skeletal muscle relaxants in the US over a 12 year period demonstrated an increasing use of cyclobenzaprine [65% of prescriptions], baclofen and tizanidine but decreasing use of metaxalone and carisoprodol).

Memorial Sloan Kettering Cancer Center

Adult Medication

This information from Lexicomp^® explains what you need to know about this medication, including what it’s used for, how to take it, its side effects, and when to call your healthcare provider.

Brand Names: US

Metaxall [DSC]; Skelaxin [DSC]

What is this drug used for?

• It is used to relax muscles.

What do I need to tell my doctor BEFORE I take this drug?

• If you are allergic to this drug; any part of this drug; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
• If you have any of these health problems: Kidney disease or liver disease.
• If you have anemia or have been told you are at risk of having anemia.

This is not a list of all drugs or health problems that interact with this drug.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take this drug?

• Tell all of your health care providers that you take this drug. This includes your doctors, nurses, pharmacists, and dentists.
• Do not take more than what your doctor told you to take. Taking more than you are told may raise your chance of very bad side effects.
• Avoid driving and doing other tasks or actions that call for you to be alert until you see how this drug affects you.
• Talk with your doctor before you use alcohol, marijuana or other forms of cannabis, or prescription or OTC drugs that may slow your actions.
• This drug is used with rest, PT (physical therapy), pain drugs, and other therapies.
• This drug may affect certain lab tests. Be sure your doctor and lab workers know you use this drug.
• If you are 65 or older, use this drug with care. You could have more side effects.
• Tell your doctor if you are pregnant, plan on getting pregnant, or are breast-feeding. You will need to talk about the benefits and risks to you and the baby.

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Fever, chills, or sore throat.
• Severe stomach pain.
• Dark urine or yellow skin or eyes.
• Feeling irritable.
• A rare but life-threatening health problem called serotonin syndrome has happened with high doses of this drug. This has also happened when normal doses of this drug were taken along with drugs for depression, migraines, or certain other drugs. Call your doctor right away if you have agitation; change in balance; confusion; hallucinations; fever; fast or abnormal heartbeat; flushing; muscle twitching or stiffness; seizures; shivering or shaking; sweating a lot; very bad diarrhea, upset stomach, or throwing up; or very bad headache.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Feeling dizzy or sleepy.
• Headache.
• Feeling nervous and excitable.
• Upset stomach or throwing up.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to your national health agency.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

How is this drug best taken?

Use this drug as ordered by your doctor. Read all information given to you. Follow all instructions closely.

• Take with or without food. Taking this drug with food may cause more sleepiness or dizziness.

What do I do if I miss a dose?

• If you take this drug on a regular basis, take a missed dose as soon as you think about it.
• If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
• Do not take 2 doses at the same time or extra doses.
• Many times this drug is taken on an as needed basis. Do not take more often than told by the doctor.

How do I store and/or throw out this drug?

• Store at room temperature in a dry place. Do not store in a bathroom.
• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.

General drug facts

• If your symptoms or health problems do not get better or if they become worse, call your doctor.
• Do not share your drugs with others and do not take anyone else’s drugs.
• Some drugs may have another patient information leaflet. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider.
• Some drugs may have another patient information leaflet. Check with your pharmacist. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider.
• If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

Consumer Information Use and Disclaimer

This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider’s examination and assessment of a patient’s specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at https://www.wolterskluwer.com/en/know/clinical-effectiveness-terms.

Last Reviewed Date

2020-07-20

Copyright

© 2023 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.

Last Updated

Monday, December 12, 2022

Metaxalone – instructions for use

Metaxalone

Instruction:

• Pharmacological action
• Pharmacokinetics
• Readings
• Contraindications
• Pregnancy and breastfeeding
• Pediatric use
• Use in elderly patients
• Dosage and Administration
• Side effects
• Precautions
• Transport management
• Classification

Pharmacological action

Metaxalone is a central muscle relaxant. The mechanism of action is not fully understood, presumably associated with a general depression of the central nervous system.

Pharmacokinetics

Absorption

Maximum plasma concentration (C _max ) – 296 mcg / ml. Time to reach maximum plasma concentration (TC _max ) – 3 hours.

Onset within 1 hour, duration 4-6 hours.

Distribution

Distribution volume (V _d ) – 800 l.

Metabolism

Biotransformed in the liver.

Elimination

Half-life (T _½ ) – 4-14 hours. About Excreted in the urine.

Indications

Painful muscle spasm in diseases and injuries of the musculoskeletal system.

Contraindications

Hypersensitivity; drug hemolytic anemia in history; significant renal/liver failure.

Pregnancy and breastfeeding

Use in pregnancy

FDA fetal category C.

Adequate and well-controlled clinical studies of the safety of metaxalone during pregnancy have not been conducted. It is not known whether the drug has immediate or delayed adverse effects on the fetus.

Animal studies showed no evidence of impaired fertility or harm to the fetus.

The use of metaxalone in pregnant women is contraindicated.

Use during breastfeeding

Special studies on the safety of the use of metaxalone during breastfeeding have not been conducted.

It is not known whether metaxalone is excreted in breast milk. A risk to the infant cannot be ruled out.

If necessary, the use of the drug during lactation should stop breastfeeding.

Pediatric use

Safety and efficacy in children under 12 years of age have not been established.

Use in elderly patients

Worse tolerated in elderly patients.

Dosage and Administration

Children over 12 years of age and adults: Orally, 800 mg 3-4 times a day.

Side effects

The frequency of occurrence of adverse reactions has not been determined: gastrointestinal disorders, nausea, vomiting, dizziness, headache, drowsiness, nervousness, hemolytic anemia (rare), leukopenia (rare), jaundice (rare), hypersensitivity (rare).

Precautions

CNS depression may occur

Increased sedation may occur when combined with other sedatives.

Bioavailability may be increased in women.

Influence on the ability to drive vehicles and control mechanisms

Due to the fact that metaxalone can cause dizziness and drowsiness, it is necessary to refrain from driving vehicles and engaging in activities that require increased concentration of attention and speed of psychomotor reactions.

Classification

• Pharmacological group

  n-anticholinergics (muscle relaxants)

• FDA pregnancy category

  C
  (risk not excluded)

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More on the topic

Find out more about the active ingredient Metaxalone: ​​

• Reviews
• Questions
• Latin name
• Chemical formula

Information about the active substance Metaxalone is intended for medical and pharmaceutical professionals, for reference purposes only. The instructions are not intended to replace professional medical advice, diagnosis or treatment. The information contained here may change over time. The most accurate information on the use of drugs containing the active substance Metaxalone is contained in the manufacturer’s instructions attached to the package.

Metaxalone (skelaxin): side effects, dosages, treatments, interactions, warnings

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• What is
  • What is metaxalone and how does it work?
• Side effects
  • What side effects are associated with the use of metaxalone?
• Drug interactions
  • What other drugs interact with metaxalone?
• Warnings and precautions
  • What are the warnings and precautions for metaxalone?

Trade name: Skelaxin

Generic name: metaxalone

Drug class: skeletal muscle relaxants

What is metaxalone and how does it work?

Metaxalone is a skeletal muscle relaxant indicated for the short-term treatment of painful muscle spasms.

Metaxalone is marketed under the following trade names: Skelaxin.

Metaxalone dosages:

Dosage forms and strengths

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Tablet

• 800mg

Dosage Recommendation:

Musculoskeletal pain

• Indicated for acute, painful musculoskeletal conditions

900 05 Adults: 800 mg orally every 6 to 8 hours.

• Children 12 years of age and older: 800 mg orally every 6 to 8 hours.
• Children under 12 years of age: Safety and efficacy not established.

Dosage Modifications

Renal Insufficiency

• Mild to Moderate Disorders: Use caution.
• Severe violation: contraindicated.

Liver failure

• Mild to moderate impairment: use caution.
• Severe violation: contraindicated.

What side effects are associated with the use of metaxalone?

Side effects of metaxalone include:

• Gastrointestinal drug-induced disorders
• Indigestion
• Nausea
• Vomiting
• Dizziness 9000 6
• Headache
• Drowsiness
• Nervousness
• Irritability
• Skin rash
• Hemolytic anemia (rare)
• Low white blood cell count (leukopenia) (rare)
• Immune hypersensitivity reaction (rare)

Serious side effects of metaxalone include:

• Abdominal pain
• Loss of appetite 9000 6
• Low fever
• Dark urine
• Clay colored stools
• Yellowing of the skin and eyes (jaundice) (rare)

This leaflet does not contain all possible side effects that may occur. For more information about side effects, please consult your doctor.

What other drugs interact with metaxalone?

If your doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and can monitor you for them. Do not start, stop, or change the dosage of any medicine without talking to your doctor, health care provider, or pharmacist.

Botox side effects for migraine

Severe interactions with metaxalone include:

• Idelalisib
• ivacaftor
• sodium oxybate

Metaxalone interacts moderately with at least 160 different drugs.

Mild interactions of metaxalone include:

• eucalyptus
• sage

This information does not contain all possible interactions or side effects. Therefore, before using this product, tell your doctor or pharmacist about all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Consult your healthcare professional or physician for additional medical advice, or if you have any health questions, concerns, or additional information about this medicine.

What are the warnings and precautions for metaxalone?

Warnings

This medicine contains metaxalone. Do not take skelaxin if you are allergic to metaxalone or any of the ingredients in this medicine.

Keep out of reach of children. In case of overdose, seek medical attention or contact a Poison Control Center immediately.

Contraindications.

• Hypersensitivity
• History of drug-induced hemolytic anemia
• Significant renal/hepatic impairment

Effects of drug abuse

Timolol maleate ophthalmic gel solution

• None

Short-term effects

• See “What side effects are associated with the use of metaxalone?”

Long-term effects

• See “What side effects are associated with the use of metaxalone?”

Warnings

• Central nervous system (CNS) depression may occur.
• Sedation may be increased when used with other sedatives.
• Drugs are poorly tolerated by the elderly
• Bioavailability may be increased in female patients.