800 mg oval, scored pink tablet. Each tablet contains 800 mg metaxalone and the following inactive skelaxin controlled substance: alginic acid, ammonium calcium alginate, B-Rose Liquid, corn starch, and magnesium stearate. Metaxalone has no direct action on the contractile mechanism of striated muscle, the motor end plate, or the nerve fiber.

Pharmacokinetics The pharmacokinetics of metaxalone have been evaluated in healthy adult volunteers after single dose administration of Skelaxin under fasted and fed conditions at doses ranging from 400 mg to 800 mg. Absorption Peak plasma concentrations of metaxalone occur approximately 3 hours after a 400 mg oral dose under fasted conditions. Thereafter, metaxalone concentrations decline log-linearly with a terminal half-life of 9. Dose proportionality at doses above 800 mg has not been studied.

The absolute bioavailability of metaxalone is not known. The single-dose pharmacokinetic parameters of metaxalone in two groups of healthy volunteers are shown in Table 1. 400 mg Skelaxin tablet under fasted conditions and following a standard high-fat breakfast. Similar food effect results were observed in the above study when one Skelaxin 800 mg tablet was administered in place of two Skelaxin 400 mg tablets.

Metaxalone is metabolized by the liver and excreted in the urine as unidentified metabolites. Metaxalone does not significantly inhibit major CYP enzymes such as CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. The results were analyzed separately, as well as in combination with the results from three other studies. The bioavailability of metaxalone under fasted and fed conditions in three groups of healthy volunteers of varying age is shown in Table 2. 1 hours in females and 7.

Similar findings were also seen when the previously described combined dataset was used in the analysis. Renal Insufficiency The impact of hepatic and renal disease on the pharmacokinetics of metaxalone has not been determined. The mode of action of this drug has not been clearly identified, but may be related to its sedative properties. Metaxalone does not directly relax tense skeletal muscles in man. Contraindications Known hypersensitivity to any components of this product. Known tendency to drug induced, hemolytic, or other anemias.

Significantly impaired renal or hepatic function. The onset of symptoms generally occurs within several hours to a few days, but may occur later than that. Discontinue Skelaxin if serotonin syndrome is suspected. Exercise caution with patients who take more than one of these CNS depressants simultaneously.

Precautions Skelaxin should be administered with great care to patients with pre-existing liver damage. Serial liver function studies should be performed in these patients. False-positive Benedict’s tests, due to an unknown reducing substance, have been noted. A glucose-specific test will differentiate findings.