Metaxalone

Oral
Acute musculoskeletal disorders

Drug-induced haemolytic anaemia or other anaemias. Significantly impaired hepatic or renal function.

Concomitant use with serotonergic agents (e.g. SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, MAOIs). Hepatic and renal impairment. Pregnancy and lactation.

Significant: CNS depression.
Blood and lymphatic system disorders: Haemolytic anaemia, leucopenia.
Gastrointestinal disorders: Nausea, vomiting, gastrointestinal distress.
Immune system disorders: Hypersensitivity reaction, anaphylaxis. Rarely, anaphylactoid reaction.
Nervous system disorders: Dizziness, headache, drowsiness, nervousness, irritability.
Skin and subcutaneous tissue disorders: Rash (with or without pruritus), jaundice.
Potentially Fatal: Serotonin syndrome when used with serotonergic agents (e.g. SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, MAOIs).

This medicine may cause drowsiness or dizziness, if affected, do not drive or operate machinery.

Symptoms: Serotonin syndrome, death. Management: Supportive therapy. Perform gastric lavage.

Increased risk of serotonin syndrome with other serotonergic agents (e.g. SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, MAOIs). Enhanced sedative effects with benzodiazepines.

Enhanced CNS depressant effect with alcohol.

May cause false-positive results for glucose determinations using cupric sulfate (e.g. Benedict’s solution, Fehling’s solution).

Description: Metaxalone is a centrally acting muscle relaxant. The precise mechanism of action has not been established. Its effect may be associated with CNS depression. It has no direct effect on the contractile mechanism of striated muscle, the motor end plate or the nerve fibre.
Onset: Within 1 hour.
Duration: 4-6 hours.
Pharmacokinetics:
Absorption: Absorbed from the gastrointestinal tract. Bioavailability: May be increased with food. Time to peak plasma concentration: Approx 3 hours.
Distribution: Extensively distributed in the tissues. Volume of distribution: Approx 800 L.
Metabolism: Metabolised in the liver by CYP1A2, CYP2D6, CYP2E1, CYP3A4 and to a lesser extent by CYP2C8, CYP2C9, and CYP2C19.
Excretion: Via urine (as metabolites). Elimination half-life: 9±4.8 hours.

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 15459, Metaxalone. https://pubchem.ncbi.nlm.nih.gov/compound/Metaxalone. Accessed Apr. 28, 2021.

Store between 15-30°C.

Muscle Relaxants

Anon. Metaxalone. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 18/02/2021.

Anon. Metaxalone. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 18/02/2021.

Buckingham R (ed). Metaxalone. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 18/02/2021.

Metaxalone (Actavis Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 18/02/2021.

Skelaxin (Pfizer Laboratories Div Pfizer Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 18/02/2021.