Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ROBAXIN-750 vs CYCLOBENZAPRINE HYDROCHLORIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Methocarbamol, the active ingredient in Robaxin-750, is a centrally acting muscle relaxant. Its precise mechanism is not fully understood, but it is believed to cause general central nervous system depression, possibly through inhibition of polysynaptic reflexes at the spinal cord level.
Cyclobenzaprine is a centrally acting muscle relaxant that reduces tonic somatic motor activity at the supraspinal level, primarily at the brainstem reticular formation and descending pathways. It is structurally related to tricyclic antidepressants and inhibits reuptake of norepinephrine and serotonin, but the direct relationship to its muscle relaxant effects is not fully established.
Adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions
Treatment of muscle spasm associated with acute, painful musculoskeletal conditions (FDA approved),Adjunct to rest and physical therapy for relief of muscle spasm (FDA approved)
750 mg orally four times daily (total daily dose 3000 mg).
Adults: 5 mg orally three times daily; may increase to 10 mg three times daily based on response. Maximum 30 mg per day.
Terminal elimination half-life: 1-2 hours (methocarbamol); clinical context: short half-life necessitates frequent dosing (q6h) and may lead to fluctuating plasma levels.
Terminal half-life: 18–24 hours (range 8–37 hours). Clinical context: requires multiple doses to achieve steady state (5–6 days); active metabolite norcyclobenzaprine has half-life ~30 hours.
Hepatic metabolism via dealkylation and hydroxylation, primarily by cytochrome P450 enzymes; metabolites are excreted renally.
Hepatic metabolism primarily via CYP3A4, CYP1A2, and CYP2D6; also undergoes N-demethylation and glucuronidation. Active metabolites include norcyclobenzaprine.
Renal: 90-95% as metabolites (mainly conjugated), <1% unchanged; biliary/fecal: minor; <2% eliminated in feces.
Renal: ~50% as unchanged drug and metabolites; Fecal: ~40% primarily as metabolites; Biliary: minimal.
46-50% (primarily to albumin); binding is reversible and non-saturable at therapeutic concentrations.
~93% bound to albumin and alpha-1-acid glycoprotein.
0.9-1.5 L/kg (apparent Vd); clinical meaning: indicates extensive distribution into total body water and tissues, including muscle.
~5 L/kg (range 3–7 L/kg). Clinical meaning: extensive tissue distribution, including central nervous system.
Oral: about 50-75% (due to first-pass metabolism); bioavailability may vary with food (high-fat meal reduces rate but not extent).
Oral: 33–55% due to first-pass metabolism; lower for immediate-release compared to extended-release (same extent but slower absorption).
GFR 30-50 m L/min: administer 750 mg every 8 hours; GFR <30 m L/min: avoid use or administer with extreme caution; not studied in dialysis.
No specific dosing adjustment recommended; use caution in severe renal impairment due to potential accumulation.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 30-50% (e.g., 375-500 mg q6h); Child-Pugh Class C: contraindicated due to risk of hepatic encephalopathy.
Child-Pugh Class A or B: No adjustment. Child-Pugh Class C: Contraindicated due to risk of toxicity (minimal data). Use with caution in mild to moderate impairment; consider lower starting dose.
Not recommended for pediatric use; safety and efficacy not established.
Not recommended for children under 15 years; safety and efficacy not established. For adolescents ≥15 years: same as adult dosing.
Initiate at low end of dosing range (e.g., 375 mg q6h) due to increased risk of sedation and falls; monitor renal function and CNS effects.
Start with 5 mg once daily; increase slowly to a maximum of 10 mg three times daily over 2 weeks. Increased sensitivity; monitor for anticholinergic effects and sedation.
None
None
May cause drowsiness, dizziness, or blurred vision; patients should not operate machinery or drive until effects are known.,Use with caution in patients with known drug sensitivities or allergies.,May impair mental and/or physical abilities.,Seizures have been reported in patients with underlying seizure disorders or concurrent use of CNS depressants.,Serotonergic effects may occur with concurrent use of serotonergic drugs.
Serotonin syndrome risk, especially with concomitant serotonergic drugs (e.g., SSRIs, SNRIs, MAOIs),Sedation and impairment of motor skills; caution with driving or operating machinery,Anticholinergic effects (e.g., urinary retention, angle-closure glaucoma, constipation),Cardiovascular effects: tachycardia, QT prolongation, arrhythmias (especially in elderly or with pre-existing heart disease),Hepatic impairment: use with caution; reduced clearance in mild impairment, avoid in severe impairment,Withdrawal symptoms after abrupt discontinuation: dysphoria, anxiety, insomnia,Elderly patients: increased risk of falls, confusion, anticholinergic toxicity
Hypersensitivity to methocarbamol or any component of the formulation.,Patients with known or suspected myasthenia gravis.,Patients with renal impairment (due to propylene glycol content in the injectable form; oral formulation does not contain propylene glycol but should be used cautiously).
Hypersensitivity to cyclobenzaprine or any component of the formulation,Concomitant use or within 14 days of MAO inhibitors (hypertensive crisis risk),Acute recovery phase after myocardial infarction,Arrhythmias, heart block, or conduction disturbances,Hyperthyroidism,Severe hepatic impairment
Take with food to reduce gastrointestinal upset. Avoid alcohol during treatment. No specific food restrictions.
Alcohol should be avoided due to additive CNS depression. Grapefruit juice may increase cyclobenzaprine levels (though data is limited, caution is advised). High-fat meals may delay absorption but not clinically significant. No specific dietary restrictions are required.
FDA Category C: Methocarbamol has shown fetal toxicity (reduced fetal weight, increased skeletal variations) in animal studies at doses similar to human doses. First trimester: Insufficient human data; avoid unless clearly needed. Second/third trimester: Limited data; potential for musculoskeletal effects. Use only if benefit outweighs risk.
Cyclobenzaprine is classified as FDA Pregnancy Category B. Animal reproduction studies have not shown fetal risk, and there are no adequate and well-controlled studies in pregnant women. Risk cannot be ruled out. First trimester: Limited human data, but no structural anomalies reported. Second trimester: No specific adverse effects documented. Third trimester: Potential for neonatal withdrawal symptoms (e.g., jitteriness, respiratory depression) if used near term.
Methocarbamol is excreted into breast milk in small amounts; M/P ratio not established. The American Academy of Pediatrics considers it compatible with breastfeeding. Monitor infant for sedation or muscle weakness.
Cyclobenzaprine is excreted into breast milk in low amounts; the M/P ratio is unknown. Due to its anticholinergic effects, there is potential for adverse effects in the nursing infant (e.g., sedation, constipation). The American Academy of Pediatrics considers it compatible with breastfeeding, but caution is advised; alternatives may be preferred.
No specific dose adjustments recommended based on pharmacokinetic changes in pregnancy. Use lowest effective dose; IV administration should be cautious due to increased plasma volume and risk of hypotension.
No specific dose adjustments are recommended during pregnancy. Pharmacokinetic parameters (e.g., clearance) are not significantly altered by pregnancy. Use the lowest effective dose for the shortest duration due to lack of safety data.
ROBAXIN-750 (methocarbamol 750 mg) is a centrally acting muscle relaxant. It does not directly relax skeletal muscle but acts via CNS depression. Onset of action is ~30 minutes; peak effect at 2 hours. It is often used with rest, physical therapy, and NSAIDs. Contraindicated in myasthenia gravis. Doses exceeding 6 g/day may cause severe adverse effects. Tablet contains FD&C Yellow No. 5 (tartrazine), which may cause allergic reactions in susceptible individuals.
Cyclobenzaprine is structurally related to tricyclic antidepressants and shares similar anticholinergic and sedative properties. Onset of action for muscle relaxation is typically 1 hour, but maximal effect may take several days. Avoid use in patients with hyperthyroidism, cardiac disease, or those on MAOIs. Not recommended for use longer than 2-3 weeks due to lack of evidence for chronic use. Caution in elderly due to anticholinergic effects and fall risk.
Take exactly as prescribed; do not increase dose or frequency without consulting your doctor.,This medication may cause drowsiness, dizziness, or blurred vision; avoid driving or operating machinery until you know how it affects you.,Avoid alcohol and other CNS depressants (e.g., sedatives, tranquilizers) as they may increase sedation.,Notify your doctor if you have myasthenia gravis, allergies to tartrazine (FD&C Yellow No. 5), or if you are pregnant or breastfeeding.,May discolor urine (brown, black, or blue-green); this is harmless.,Do not stop suddenly; withdrawal symptoms (e.g., anxiety, insomnia) may occur with abrupt discontinuation after prolonged use.
This medication may cause drowsiness, dizziness, or blurred vision; avoid driving or operating machinery until you know how it affects you.,Do not drink alcohol or use other CNS depressants (e.g., benzodiazepines, opioids) while taking this medication, as it may increase sedation.,Take this medication exactly as prescribed, usually 3 times a day. Do not take more or less than directed.,This medication is intended for short-term use (up to 2-3 weeks) for muscle spasm. Do not use it for longer without consulting your doctor.,If you experience dry mouth, try sucking on sugar-free candy or ice chips. If you have difficulty urinating or vision changes, contact your doctor.,Do not stop taking this medication abruptly without consulting your doctor, although withdrawal is uncommon with short-term use.
No interactions on record
"The combination of cyclobenzaprine and carbinoxamine results in additive central nervous system depression due to their shared anticholinergic and sedative properties. This can lead to excessive sedation, impaired cognitive and motor function, and increased risk of falls or accidents. Severe cases may result in respiratory depression, especially in elderly patients or those with preexisting conditions."
"Cyclobenzaprine, a centrally acting muscle relaxant with tricyclic antidepressant (TCA)-like structure, and Dezocine, an opioid partial agonist analgesic with mu-opioid receptor activity, both depress the central nervous system (CNS) and have additive serotonergic effects. Concomitant use increases the risk of excessive CNS depression, manifesting as sedation, respiratory depression, and impaired psychomotor function, as well as potential serotonin syndrome due to combined serotonergic activity. Clinically, patients may experience profound drowsiness, confusion, respiratory compromise, and in severe cases, coma or death from respiratory failure."
"Lumacaftor, a potent inducer of cytochrome P450 (CYP) 3A4, significantly reduces the systemic exposure of cyclobenzaprine, a CYP3A4 substrate. This results in decreased plasma concentrations of cyclobenzaprine, potentially leading to reduced therapeutic efficacy for muscle spasm relief. Patients may require dose adjustments or alternative therapies to maintain clinical benefit."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ROBAXIN-750 vs CYCLOBENZAPRINE HYDROCHLORIDE, answered by our medical review team.
ROBAXIN-750 is a Skeletal Muscle Relaxant that works by Methocarbamol, the active ingredient in Robaxin-750, is a centrally acting muscle relaxant. Its precise mechanism is not fully understood, but it is believed to cause general central nervous system depression, possibly through inhibition of polysynaptic reflexes at the spinal cord level.. CYCLOBENZAPRINE HYDROCHLORIDE is a Skeletal Muscle Relaxant that works by Cyclobenzaprine is a centrally acting muscle relaxant that reduces tonic somatic motor activity at the supraspinal level, primarily at the brainstem reticular formation and descending pathways. It is structurally related to tricyclic antidepressants and inhibits reuptake of norepinephrine and serotonin, but the direct relationship to its muscle relaxant effects is not fully established.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ROBAXIN-750 and CYCLOBENZAPRINE HYDROCHLORIDE depend on the specific clinical indication. These are both Skeletal Muscle Relaxant agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ROBAXIN-750 is: 750 mg orally four times daily (total daily dose 3000 mg).. The standard adult dose of CYCLOBENZAPRINE HYDROCHLORIDE is: Adults: 5 mg orally three times daily; may increase to 10 mg three times daily based on response. Maximum 30 mg per day.. 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 ROBAXIN-750 and CYCLOBENZAPRINE HYDROCHLORIDE 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. ROBAXIN-750 is classified as Category C. FDA Category C: Methocarbamol has shown fetal toxicity (reduced fetal weight, increased skeletal variations) in animal studies at doses similar to human doses. First trimester: Ins. CYCLOBENZAPRINE HYDROCHLORIDE is classified as Category A/B. Cyclobenzaprine is classified as FDA Pregnancy Category B. Animal reproduction studies have not shown fetal risk, and there are no adequate and well-controlled studies in pregnant . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.