Metaxalone Oral: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing

See also How to Use section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor’s approval.

Some products that may interact with this drug include: diet pills/appetite suppressants (such as diethylpropion), drugs for attention deficit disorder (such as atomoxetine, methylphenidate), apraclonidine, bupropion, buspirone, carbamazepine, cyclobenzaprine, deutetrabenazine, a certain combination product (dextromethorphan/quinidine), levodopa, maprotiline, methyldopa, metoclopramide, certain opioid pain relievers (such as fentanyl, meperidine, methadone, tapentadol), certain drugs for Parkinson’s disease (such as entacapone, tolcapone), certain supplements (such as tryptophan, tyramine), tetrabenazine, tricyclic antidepressants (such as amitriptyline, doxepin), valbenazine.

The risk of serotonin syndrome/toxicity increases if you are also taking other drugs that increase serotonin. Examples include street drugs such as MDMA/”ecstasy,” St. John’s wort, certain antidepressants (including mirtazapine, SSRIs such as fluoxetine/paroxetine, SNRIs such as duloxetine/venlafaxine), tramadol, certain “triptans” used to treat migraine headaches (such as rizatriptan, sumatriptan, zolmitriptan), among others. The risk of serotonin syndrome/toxicity may be more likely when you start or increase the dose of these drugs.

Some products can interact with metaxalone if you take them together, or even if you take them weeks before or after taking metaxalone. Tell your doctor or pharmacist if you take anything in the list of products that may interact with this drug, or any of the products that increase serotonin, within 2 weeks before or after taking metaxalone. Also tell them if you have taken fluoxetine within 5 weeks before starting metaxalone. Ask your doctor how much time to wait between starting or stopping any of these drugs and starting metaxalone.

Taking other MAO inhibitors with this medication may cause a serious (possibly fatal) drug interaction. Do not take any other MAO inhibitors (isocarboxazid, linezolid, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, safinamide, selegiline, tranylcypromine) during treatment with this medication. Most MAO inhibitors should also not be taken for two weeks before and after treatment with this medication. Ask your doctor when to start or stop taking this medication.

Before using metaxalone, report the use of drugs that may increase the risk of extremely high blood pressure (hypertensive crisis) when combined with metaxalone, including herbal products (such as ephedra/ma huang), nasal decongestants (such as phenylephrine, pseudoephedrine), and stimulants (such as amphetamines, ephedrine, epinephrine, phenylalanine). Metaxalone should not be used with any of these medications. Talk to your doctor or pharmacist for more details.

Tell your doctor or pharmacist if you are taking other products that cause drowsiness such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana (cannabis), drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), other muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

This medication may interfere with certain lab tests (such as certain urine glucose tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.

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Metaxalone: MedlinePlus Drug Information

pronounced as (me tax’ a lone)

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Metaxalone, a muscle relaxant, is used with rest, physical therapy, and other measures to relax muscles and relieve pain and discomfort caused by strains, sprains, and other muscle injuries.

Metaxalone comes as a tablet to take by mouth. It usually is taken three or four times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take metaxalone exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

Before taking metaxalone,

• tell your doctor and pharmacist if you are allergic to metaxalone, any other medications, or any of the ingredients in metaxalone tablets. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take while taking metaxolone. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• tell your doctor if you have or have ever had kidney disease, liver disease, seizures, or a blood disorder.
• tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking metaxalone, call your doctor immediately.
• talk to your doctor about the risks and benefits of taking metaxalone if you are 65 years of age or older. Older adults should not usually take metaxalone because it is not as safe or effective as other medications that can be used to treat the same condition.
• you should know that this drug may make you drowsy. Do not drive a car or operate machinery until you know how metaxalone affects you.
• remember that alcohol can add to the drowsiness caused by this drug.

Take the missed dose as soon as you remember it. However, if it is almost time for your next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Metaxalone may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• drowsiness
• dizziness
• headache
• nervousness

If you experience any of the following symptoms, call your doctor immediately:

• agitation, hallucinations, coma
• fast heart rate, high body temperature
• muscle twitching, loss of muscle control
• nausea, vomiting, diarrhea
• severe skin rash
• difficulty breathing
• yellowing of the skin or eyes
• unusual bruising or bleeding
• unusual tiredness or weakness
• seizures

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature, away from excess heat and moisture (not in the bathroom).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA’s Safe Disposal of Medicines website (http://goo. gl/c4Rm4p) for more information if you do not have access to a take-back program.

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can’t be awakened, immediately call emergency services at 911.

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Carcinogenesis, mutagenesis, impaired fertility

The carcinogenic potential of metaxalone has not been determined.

Pregnancy

Reproduction studies in rats showed no evidence of impaired fertility or fetal harm due to metaxalone. Post-marketing experience has not shown any evidence of fetal injury, but such experience cannot rule out the possibility of rare or subtle injury to the human fetus. The safe use of metaxalone has not been demonstrated in relation to possible adverse effects on fetal development. Therefore, metaxalone tablets should not be used in women who are or may be pregnant, especially during early pregnancy, unless the physician considers that the potential benefits outweigh the potential hazards.

Nursing mothers

It is not known if this drug is excreted in breast milk. As a general rule, caution should not be exercised when taking medications, as many medications are excreted in breast milk.

Pediatric use

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

Overdose and Contraindications

Intentional or accidental overdose deaths have occurred with metaxalone, especially when combined with antidepressants, and this class of drug has been reported in combination with alcohol.

Serotonin syndrome has been reported when metaxalone was used at doses above the recommended dose layers (see WARNINGS ).

When determining LD ₅₀ progressive sedation, hypnosis and finally respiratory failure were found in rats and mice with increasing dosage. No LD can be found in dogs ₅₀ is determined because higher doses were emetic after 15-30 minutes.

Treatment

Gastric lavage and supportive care. It is recommended that you consult with your regional gift management center.

PRICE

Hypersensitivity to components of this product is known.

Known tendency to drug-induced, hemolytic or other anemia.

Significantly impaired renal or hepatic function.

Clinical pharmacology

CLINICAL PHARMACOLOGY

Mechanism of action

The mechanism of action of metaxalone in humans has not been established, but it can be attributed to a general depression of the central nervous system.

Metaxalone has no direct effect on the contractile mechanism of the striated muscle, motor end plate or nerve fiber.

Pharmacokinetics

The pharmacokinetics of metaxalone was studied in healthy adult volunteers after a single dose of metaxalone in sober and well-fed conditions at doses ranging from 400 to 800 mg.

Absorption

Peak plasma concentrations of metaxalone occur approximately 3 hours after an oral dose of 400 mg under sober conditions. The logarithmic concentrations of metaxalone then decrease with a finite half-life of 9.0 ± 4.8 hours. Doubling the dose of Metaxalone from 400 mg to 800 mg results in an approximately proportional increase in Metaxalone exposure as evidenced by peak plasma concentrations (Cmax) and area under the curve (AUC). Dose proportionality at doses above 800 mg has not been studied. The absolute bioavailability of metaxalone is not known.

Pharmacokinetic parameters of single dose metaxalone in two groups of healthy volunteers are shown in Table 1.

Table 1: Mean (% CV) pharmacokinetic parameters of Metaxalone

Dose (mg)	Cmax (ng/ml)	Tmax (h)	AUC∞ (ng & ml; h/ml)	t½ (h)	CL / F ( L / h)
400 1	983 (53)	3. 3 (35)	7479 (51)	9, 0 (53)	68 (50)
800 2	1816 (43)	3.0 (39)	15044 (46)	8.0 (58)	66 (51)
1 Subjects received 1x400mg tablet sober (N = 42) 2 Subjects received 2x400mg tablets sober conditions (N = 59)

Food Effects

A randomized, bi-directional, crossover study was conducted in 42 healthy volunteers (31 males, 11 females) who administered a Metaxalone 400 mg tablet while sober and after a standard high-fat breakfast. Subjects ranged from 18 to 48 years (mean age = 23.5 ± 5.7 years). Compared to sober states, the presence of a high-fat meal increased by 177.5% during drug C administration and increased AUC (AUC0-t, AUC∞) by 123.5% and 115.4%, respectively. Time to peak concentration (Tmax) was also delayed (4.3 hours vs. 3.3 hours) and the terminal half-life was reduced (2. 4 hours vs. 9.0 hours) under feeding conditions compared with fasting.

In a second study with a similar effect, healthy volunteers (N = 59, 37 males, 22 females) were given two tablets of metaxalone 400 mg (800 mg) aged 18-50 years (mean age = 25). 6 ± 8.7 years). Compared to sober states, the presence of a high-fat meal increased by 193.6% during drug C administration and increased AUC (AUC0-t, AUC, ∞) by 146.4% and 142.2%, respectively. Time to Peak concentration (Tmax) was also delayed (4.9h versus 3.0 h), and the terminal half-life was shortened (4.2 h compared to 8.0 h) under fed versus fasting conditions. Similar nutritional effects were observed in the aforementioned study when a Metaxalone tablet was administered instead of two 400 mg Metaxalone tablets. An increase in metaxalone exposure, which coincides with a decrease in half-life, may be due to more complete absorption of metaxalone in the presence of a high-fat meal (Figure 1).

Figure 1: Mean (SD) concentrations of metaxalone after a dose of 800 mg under fasting and feeding conditions

Distribution, metabolism and elimination

Although plasma protein binding and absolute bioavailability of metaxalone are unknown, the apparent volume of distribution (V/F 800 L) and lipophilia (log P = 2. 42) of metaxalone indicate that the drug is mainly distributed in tissues. Metaxalone is metabolized in the liver and excreted in the urine as unidentified metabolites. Hepatic cytochrome P450 enzymes play a role in the metabolism of metaxalone. In particular, CYP1A2, CYP2D6, CYP2E1 and CYP3A4 and to a lesser extent CYP2C8, CYP2C9and CYP2C19 metabolize metaxalone.

Metaxalone does not significantly inhibit major CYP enzymes such as CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4. Metaxalone does not cause significant induction of important CYP enzymes such as CYP1A2, CYP2B6 and CYP3A4 in vitro .

Pharmacokinetics in special populations

Age

The effect of age on the pharmacokinetics of metaxalone was determined after a single administration of two 400 mg (800 mg) tablets under fasting and feeding conditions. The results were evaluated separately, as well as in combination with the results of three other studies. Using the combined data, the results show that the pharmacokinetics of metaxalone under sober conditions is significantly more dependent on age than under feeding, with bioavailability increasing with age under sober conditions.

The fasting and feeding bioavailability of metaxalone in three groups of healthy volunteers of different ages is shown in Table 2.

Table 2: Mean pharmacokinetic parameters (% CV) feeding

Gender

in which 48 healthy adult subjects (24 men, 24 women) were administered, two tablets of metaxalone 400 mg (800 mg) in sober conditions. The bioavailability of metaxalone was significantly higher in women than in men than Cmax (2115 ng/ml vs 1335 ng/ml) and AUC∞ (17884 ng h/ml vs 10328 ng h/ml). The mean half-life was 11.1 hours for women and 7.6 hours for men. The apparent volume of distribution of metaxalone was approximately 22% higher in men than in women, but the difference was not significant when adjusted for body weight. Similar results were also seen when the previously described combined data set was used in the analysis.

Liver/renal failure

The effect of liver and kidney disease on the pharmacokinetics of metaxalone has not been determined. In the absence of such information, Metaxalone should be used with caution in patients with hepatic and/or renal insufficiency.

Skelaxin (Metaxalone): Uses, Dosage, Side Effects, Interactions, Warning0294 Product Description