Metaxalone: uses, dosing, side effects & brands

Metaxalone is a muscle relaxant used to treat Muscle Cramp, Muscle Rigidity, Muscle Spasticity, Myositis.

The FDA classifies metaxalone as a muscle relaxant. Most muscle relaxants work in the brain and spinal cord rather than on the muscle itself: they damp down the overactive nerve signals and reflexes that keep muscles tense, easing spasms and tightness. Some specialized agents instead act directly on muscle calcium release. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

The elimination half-life of metaxalone is about 9 hours (terminal half-life 9.0 ± 4.8 hours after a 400 mg oral dose, fasted; ~8 hours at 800 mg) — that is how long the body takes to clear half of a dose. This is the terminal (elimination) half-life the label reports; the label describes single log-linear (terminal) decline, not a separate distribution phase. Metaxalone is NOT a prodrug and the label names no active metabolite — it is hepatically metabolized to "unidentified metabolites" excreted in urine, so no metabolite outlasting the parent is described. Half-life is markedly shortened by food: with a high-fat meal it fell to ~2.4 h (vs 9.0 h) at 400 mg and ~4.2 h (vs 8.0 h) at 800 mg, alongside more complete absorption and higher exposure. Sex difference: mean half-life ~11.1 h in females vs ~7.6 h in males, with higher exposure in females. Age: the label does not give a separate elderly half-life but says metaxalone PK is significantly more affected by age under fasted conditions, with bioavailability/exposure rising with age (AUC∞ ~15,000 in ~26-yr-olds vs ~24,000 ng·h/mL in ~72-yr-olds at 800 mg fasted). Hepatic/renal impairment: the label states the impact of hepatic and renal disease on metaxalone PK has NOT been determined and advises using it with caution in these patients — so no adjusted half-life is available. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run metaxalone against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 2 metaxalone-containing products in the U.S.: Metaxalone and Skelaxin. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, metaxalone is currently marketed as tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Yes. Our catalog lists 1 generic metaxalone product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.