Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
METAXALONE vs ACTIQ
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Metaxalone is a centrally acting muscle relaxant whose exact mechanism is unknown. It is thought to produce skeletal muscle relaxation by depressing the central nervous system (CNS), possibly through general CNS depression or by blocking polysynaptic reflexes in the spinal cord.
Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.
FDA-approved: Adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.,Off-label: Management of muscle spasms, spasticity.
Management of breakthrough pain in cancer patients aged 16 and older who are already receiving and tolerant to opioid therapy for their underlying persistent cancer pain
800 mg orally 3 to 4 times daily
200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.
Terminal elimination half-life is approximately 0.5 to 1.5 hours, reflecting rapid clearance and supporting short-lived clinical effects.
Terminal half-life 0.83–2 hours (mean 1.3 h) in adults; note that context: transmucosal absorption leads to rapid onset but short duration; half-life is not correlated with clinical effect due to oral transmucosal route and rapid redistribution.
Extensively metabolized in the liver via cytochrome P450 enzymes (CYP1A2, CYP2D6, CYP3A4, CYP2C19, and CYP2E1) to unidentified metabolites. Less than 1% excreted unchanged in urine.
Primarily hepatic via CYP3A4 to inactive metabolites (norfentanyl, despropionylfentanyl, hydroxyfentanyl) and other metabolites; <7% excreted unchanged in urine.
Primarily renal; approximately 90% of a dose is excreted in urine as glucuronide conjugates and unchanged drug, with less than 1% eliminated in feces via biliary excretion.
Primarily renal as metabolites (about 75% as metabolites, <10% unchanged). Fecal excretion accounts for <9%. Biliary excretion is minor.
Approximately 98% bound to plasma proteins, primarily albumin.
Fentanyl is 80–85% bound to plasma proteins (primarily albumin and α1-acid glycoprotein).
Approximately 0.3–0.5 L/kg, indicating moderate distribution into total body water and peripheral tissues.
Approximately 4 L/kg (range 3–6 L/kg); large Vd indicates extensive tissue distribution and redistribution contributing to short duration.
Oral bioavailability is high, estimated at >80% based on urinary recovery studies.
Oral transmucosal: 50% (range 47–54%) relative to IV; variable and enhanced by rapid absorption through buccal mucosa.
No specific dose adjustment guidelines available; use with caution in severe renal impairment (Cr Cl <30 m L/min) due to potential for accumulation.
No specific GFR-based dose adjustment recommended; use with caution in severe renal impairment (Cr Cl < 30 m L/min) and consider dose reduction due to potential accumulation.
No specific dose adjustment guidelines available; use with caution in severe hepatic impairment (Child-Pugh class C) as metabolism may be reduced.
Child-Pugh Class A/B: No adjustment. Child-Pugh Class C: Reduce initial dose to 100 mcg and titrate slowly; monitor closely for prolonged effects.
Safety and efficacy not established; not recommended for use in children under 12 years of age.
Not approved for pediatric use; safety and efficacy not established in patients under 16 years.
Start at lower end of dosing range (e.g., 800 mg 3 times daily) due to increased sensitivity and risk of adverse effects; monitor closely.
Initiate at 100 mcg transmucosally; titrate slowly due to increased sensitivity and risk of respiratory depression. Monitor for adverse effects.
None.
Risk of respiratory depression, addiction, abuse, and misuse; accidental ingestion can be fatal; concomitant use with benzodiazepines or CNS depressants may cause profound sedation, respiratory depression, coma, and death; not for use in opioid non-tolerant patients; risk of neonatal opioid withdrawal syndrome with prolonged use during pregnancy; serious, life-threatening, or fatal respiratory depression may occur even at recommended doses.
Serotonin syndrome risk when co-administered with serotonergic drugs (e.g., SSRIs, SNRIs, MAOIs).,Hepatic toxicity: rare reports of liver injury; use caution in patients with hepatic impairment.,CNS depressant effects: may impair mental and physical abilities; avoid concurrent alcohol or other CNS depressants.,Elderly may be more sensitive to sedative effects.
Risk of respiratory depression; addiction, abuse, and misuse; interactions with CNS depressants; serotonin syndrome; adrenal insufficiency; severe hypotension; seizures; withdrawal; use in patients with head injuries, increased intracranial pressure, biliary tract disease, pancreatitis; risk of choking with lozenge; oral mucosal irritation; dental caries; hypokalemia; hyponatremia; use in elderly, cachectic, or debilitated patients.
Hypersensitivity to metaxalone or any component of the formulation.,Significant hepatic impairment (e.g., severe liver disease, cirrhosis).,History of drug-induced hemolytic anemia.,Concurrent use of MAOIs or within 14 days of MAOI therapy (potential for serotonin syndrome).
Significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment; known or suspected paralytic ileus; hypersensitivity to fentanyl or any component; opioid non-tolerant patients; management of acute or postoperative pain including headache/migraine, dental pain, or emergency department use.
Metaxalone may be taken with or without food. Grapefruit juice may increase metaxalone levels by inhibiting CYP1A2 and CYP3A4; avoid concurrent consumption. High-fat meals may slightly delay absorption but not clinically significant.
No significant food interactions. Grapefruit juice may increase fentanyl levels, but specific studies with ACTIQ are lacking. Avoid alcohol, as it may increase sedation and respiratory depression risk.
FDA pregnancy category C. No adequate studies in pregnant women. Animal studies have shown adverse effects (fetal resorptions, decreased fetal weight) at doses 5-10 times the human dose. Risk cannot be ruled out. Use only if potential benefit justifies potential risk to fetus. First trimester: Avoid; data insufficient. Second/third trimester: Limited data; may cause maternal sedation and neonatal respiratory depression if used near term.
FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause neonatal opioid withdrawal syndrome; avoid use during labor due to risk of neonatal respiratory depression.
Unknown if excreted in human milk. M/P ratio not established. Caution advised due to potential for sedation in the infant. Monitor for drowsiness, poor feeding, or weight loss. Consider alternative agents with more safety data.
Excreted in breast milk; M/P ratio not established. Limited data suggest low levels, but risk of infant sedation and respiratory depression. Avoid use while breastfeeding unless potential benefit outweighs risk.
No specific dose adjustments recommended due to lack of pharmacokinetic data in pregnancy. However, increased hepatic clearance during pregnancy may reduce drug levels; monitor clinical effect and adjust dose as needed. Use lowest effective dose for shortest duration.
Due to increased plasma volume and hepatic metabolism in pregnancy, dose requirements may increase; adjust based on clinical response and tolerance. Avoid use during labor and delivery due to risk of neonatal respiratory depression; short-term use preferred.
Metaxalone is a centrally acting muscle relaxant with a unique chemical structure (oxazolidinone derivative). It is metabolized primarily by CYP1A2 and CYP2D6; caution with inhibitors or inducers of these enzymes. Onset of action is 1-2 hours; peak effect at 3-4 hours. Due to sedative properties, avoid concurrent use with alcohol or other CNS depressants. Use with caution in elderly due to anticholinergic effects and fall risk. Metaxalone is not recommended for patients with significant hepatic impairment (Child-Pugh Class C). It has no direct effect on skeletal muscle contraction but acts on CNS polysynaptic pathways.
ACTIQ is a transmucosal immediate-release fentanyl formulation indicated for breakthrough cancer pain in opioid-tolerant patients. Initiate with the lowest strength (200 mcg) and titrate upward. Avoid use in opioid-naive patients due to risk of fatal respiratory depression. Place the unit between cheek and lower gum, not sublingually. Instruct patient not to bite or suck the unit. Monitor for sedation and respiratory depression. Multiple units may be used per episode if needed, but wait at least 4 hours before next episode. Dispose of partially used units by flushing down toilet.
Take metaxalone exactly as prescribed; do not increase dose or frequency without consulting your doctor.,May cause drowsiness or dizziness; do not drive or operate heavy machinery until you know how this medication affects you.,Avoid alcohol or other sedatives while taking metaxalone as they may worsen drowsiness.,If you miss a dose, skip the missed dose and continue with your regular schedule; do not double the dose.,Contact your healthcare provider if you experience signs of an allergic reaction (rash, hives, difficulty breathing) or jaundice (yellowing of skin/eyes).,Store at room temperature, away from moisture and heat.,Do not stop abruptly; gradual dose reduction may be recommended to prevent withdrawal symptoms.
Only use ACTIQ if you are already taking regular around-the-clock opioid pain medicine and are tolerant to opioids.,Do not use ACTIQ for short-term pain like after surgery, headache, or dental pain.,Place the unit in your cheek pouch, not under your tongue. Do not chew or suck it.,If you need more than 4 units per day, contact your doctor as your dose may need adjustment.,Store ACTIQ in a safe place away from children, as accidental ingestion can be fatal.,Dispose of unused or partially used units by flushing them down the toilet.
"The combination of Normethadone, a μ-opioid receptor agonist with respiratory depressant effects, and Metaxalone, a centrally acting muscle relaxant that also depresses the central nervous system (CNS), results in synergistic CNS depression and respiratory depression. This can lead to profound sedation, coma, or fatal respiratory failure, particularly in patients with pre-existing respiratory compromise or those taking other CNS depressants. Concomitant use increases the risk of hypotension and bradycardia due to combined cardiorespiratory depressant effects."
"The coadministration of Metaxalone and Tiagabine may lead to increased central nervous system (CNS) depression due to additive pharmacodynamic effects. Metaxalone, a centrally acting muscle relaxant, and Tiagabine, a selective GABA reuptake inhibitor, both potentiate GABAergic activity and depress neuronal excitability. This synergism can result in enhanced sedation, dizziness, ataxia, and cognitive impairment, increasing the risk of falls and respiratory depression, especially in susceptible patients."
"Concurrent use of fluticasone propionate, a corticosteroid with immunosuppressive and anti-inflammatory properties, and metaxalone, a centrally acting muscle relaxant with sedative effects, may result in additive immunosuppression and central nervous system (CNS) depression. Corticosteroids can mask signs of infection or exacerbate existing infections, while metaxalone contributes to sedation and dizziness. This combination may increase the risk of adverse effects such as heightened sedation, impaired cognitive function, and increased susceptibility to infections, particularly in elderly or debilitated patients."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about METAXALONE vs ACTIQ, answered by our medical review team.
METAXALONE is a Skeletal Muscle Relaxant that works by Metaxalone is a centrally acting muscle relaxant whose exact mechanism is unknown. It is thought to produce skeletal muscle relaxation by depressing the central nervous system (CNS), possibly through general CNS depression or by blocking polysynaptic reflexes in the spinal cord.. ACTIQ is a Opioid Analgesic that works by Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between METAXALONE and ACTIQ depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of METAXALONE is: 800 mg orally 3 to 4 times daily. The standard adult dose of ACTIQ is: 200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between METAXALONE and ACTIQ in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. METAXALONE is classified as Category A/B. FDA pregnancy category C. No adequate studies in pregnant women. Animal studies have shown adverse effects (fetal resorptions, decreased fetal weight) at doses 5-10 times the human. ACTIQ is classified as Category C. FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.