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Metaxalone

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Subjective Effects
Interactions
Tolerance
Metaxalone molecule structureMetaxalone molecule structure
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Metaxalone is a skeletal muscle relaxant1 and central nervous system depressant2 in the phenol ether chemical class. It is used to relieve pain associated with strains, sprains, and other musculoskeletal conditions, alongside rest and physical therapy. It does not directly relax tense skeletal muscles.3 Side effects include drowsiness, dizziness, nausea, and vomiting4, and it is considered a high-risk medication in older adults because of its potential side effects.

Dosage & Duration

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Dosage

Doses are population estimates that vary widely between individuals.

Threshold~400 mg
Light400-800 mg
Moderate800-1600 mg
Strong1600-2400 mg
Heavy2400+ mg

Duration

Onset15-45 minutes
After Effects1-8 hours
Total4-8 hours

Subjective Effects

Subjective Effects not written up yet

Pharmacology

Pharmacodynamics

Metaxalone's mechanism of action in humans has not been established, but its muscle-relaxant action may result from general central nervous system depression5 and its sedative properties.6 It does not directly relax tense skeletal muscles in humans.7

Pharmacokinetics

Metaxalone undergoes hepatic metabolism, with unidentified metabolites excreted in urine.7 It is a substrate of CYP1A2 and CYP2C19,4 inhibits CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A, and induces CYP1A2 and CYP3A4. Absolute oral bioavailability is unknown,6 but food increases absorption. In one study, food increased peak blood concentration by 77.5% and exposure measured by AUC0-t and AUC0-∞ by 23.5% and 15.4%, respectively, compared with fasting. The reported half-life is 9.2 ± 4.8 hours, and the volume of distribution is 800 L. Reported clearance under fasting conditions was 68 ± 50 L/h after one 400 mg tablet and 66 ± 51 L/h after two 400 mg tablets.

Metabolitesnone documented yet

Interactions

Interactions not written up yet

An unlisted combination is an unknown one, not a safe one. Check a dedicated combination chart before mixing.

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Tolerance

Tolerance not written up yet

Harm Potential

Toxicity

Lethal Dosage

During LD50 testing in rats and mice, increasing doses caused progressively deeper sedation, hypnosis, and ultimately respiratory failure.8 A canine LD50 could not be determined because higher doses induced vomiting within 15–30 minutes.9

LD50 Data
SpeciesRouteValue
RatOral775 mg/kg
MouseOral1690 mg/kg
Respiratory system

Increasing oral doses of metaxalone caused respiratory failure in rats and mice during LD50 testing.

History & Culture

On December 15, 2005, Spiridon Spireas received U.S. patent US20050276844 for bioavailable compositions of metaxalone and processes for producing them.…

Legality

International

Metaxalone is approved.

By Country

Prescription1
United States flagUnited StatesPrescription only

References

Citations

  1. Metaxalone: MedlinePlus Drug Information. MedlinePlus (2024). https://medlineplus.gov/druginfo/meds/a682010.html1
  2. Considerations for the Appropriate Use of Skeletal Muscle Relaxants for the Management Of Acute Low Back Pain. Pharmacy and Therapeutics (2014). https://pmc.ncbi.nlm.nih.gov/articles/PMC41037161
  3. Metaxalone Tablets. DailyMed (2012). https://www.dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=117c6190-77a2-2036-e054-00144ff8d46c&type=display1
  4. DailyMed — METAXALONE tablet (Direct_Rx; ANDA 203695). dailymed.nlm.nih.gov (n.d.). https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=45726fbc-3450-63f7-e063-6394a90a671a123
  5. Metaxalone: Uses, Interactions, Mechanism of Action. DrugBank (n.d.). https://go.drugbank.com/drugs/DB006601
  6. Metaxalone Monograph for Professionals. Drugs.com / ASHP (2026). https://www.drugs.com/monograph/metaxalone.html12
  7. DailyMed — METAXALONE tablet (Blenheim Pharmacal, Inc.). DailyMed (2015). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=117c6190-77a2-2036-e054-00144ff8d46c12
  8. Metaxalone Tablets. DailyMed (2024). https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=b713a0f2-d47a-0ae7-e053-2995a90a5b851
  9. metaxalone. DailyMed (2022). https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=686b8c39-4ed8-4d69-e053-2991aa0a579d1
  10. METAXALONE TABLETS, USP. DailyMed (2020). https://www.dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=168c539d-3637-4a43-a8b6-cd8e82cf6342&type=display1

Article Status

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    Step 1 · Automated synthesis

    An autonomous workflow built by Josie Kins compiled this article's foundation from information published across the web.

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