Brand name: Robaxin
Drug class: Centrally Acting Skeletal Muscle Relaxants
VA class: MS200
Chemical name: 1-Carbamate-3-(2-methoxyphenoxy)-1,2-propanediol
Molecular formula: C₁₁H₁₅NO₅
CAS number: 532-03-6

Medically reviewed by Drugs.com on Feb 14, 2025. Written by ASHP.

Introduction

Centrally acting skeletal muscle relaxant.^b

Uses for Methocarbamol

Muscular Conditions

Adjunct to rest, physical therapy, analgesics, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.^{1 2 18 110}

If pharmacologic therapy is required for acute low back pain (usually a benign and self-limiting condition),^{105 106 108} experts state that an NSAIA or skeletal muscle relaxant may be considered.¹⁰⁹ Skeletal muscle relaxants may provide small improvements in pain relief, but are associated with a high incidence of adverse effects (e.g., CNS effects).^{104 106 107 108 109} Use with caution after weighing risks against benefits.^{104 106 107 108}

Various skeletal muscle relaxants appear to have comparable efficacy for low back pain relief.^{103 104 106 108}

Methocarbamol is ineffective in the treatment of skeletal muscle hyperactivity secondary to chronic neurologic disorders (e.g., cerebral palsy) and other dyskinesias.^b

Tetanus

Has been used as an adjunct to debridement, tetanus antitoxin, penicillin, tracheotomy, fluid and electrolyte replacement, and supportive therapy in the management of tetanus.^{2 b} However, most authorities prefer other sedatives or muscle relaxants (e.g., diazepam) and, in severe cases, neuromuscular blocking agents.^b

Methocarbamol Dosage and Administration

Administration

Administer orally; may administer IV or IM when oral administration is not feasible or for severe musculoskeletal pain.^{1 2 b} Do not administer sub-Q.²

Oral Administration

NG Tube

For administration via NG tube, crush tablets and suspend in water or saline solution.²

IV Administration

For solution compatibility information, see Compatibility under Stability.

Administer undiluted by direct IV injection (at a rate not exceeding 3 mL/minute), or dilute and administer by IV infusion.²

Patient should be recumbent during and for 10–15 minutes following IV administration.²

Avoid extravasation; solution is hypertonic.²

Blood aspirated into syringe does not mix with methocarbamol injection; either inject any blood in the syringe or stop the injection when the plunger reaches the blood.²

Dilution

For IV infusion, dilute 1 g with up to 250 mL of 5% dextrose or 0.9% sodium chloride injection.²

Rate of Administration

For direct IV injection, maximum rate of 3 mL/minute.²

IM Administration

Administer no more than 500 mg (5 mL of the 100-mg/mL injection) into each gluteal region.²

Dosage

Pediatric Patients

Tetanus

IV

Recommended minimum initial dose is 15 mg/kg or 500 mg/m²; may give additional doses of 15 mg/kg or 500 mg/m² by direct IV injection or IV infusion every 6 hours, if necessary (maximum 1.8 g/m² daily for 3 consecutive days).²

Adults

Muscular Conditions

Oral

Usual initial dosage is 1.5 g 4 times daily for 2–3 days.¹ For maintenance, decrease dosage to 4–4.5 g daily in 3–6 divided doses.¹

Patients with severe symptoms may require initial dosage of 8 g daily in divided doses.¹

IV or IM

Usually, 1 g as a single dose, followed by oral methocarbamol to maintain relief.²

For more severe conditions or when oral administration is not feasible, additional doses of 1 g may be administered every 8 hours (maximum 3 g daily for 3 consecutive days).² If necessary, may readminister IM or IV after a 48-hour drug-free interval.²

Tetanus

IV, then Oral

Recommended initial dose is 1–2 g by direct IV injection; may administer additional 1–2 g by IV infusion (for total initial dose of up to 3 g).²

Repeat dosage regimen every 6 hours until NG tube can be inserted.² May then administer crushed tablets suspended in water or saline through NG tube.² Up to 24 g daily (via NG tube) may be required.²

Prescribing Limits

Pediatric Patients

Tetanus

IV

Maximum 1.8 g/m² daily for 3 consecutive days.²

Adults

Muscular Conditions

IV or IM

Maximum 3 g daily for 3 consecutive days.²

Cautions for Methocarbamol

Contraindications

• Injection contraindicated in patients with impaired renal function.² (See Renal Impairment under Cautions.)

• Known hypersensitivity to methocarbamol or any ingredient in the formulation.^{1 2}

Warnings/Precautions

Warnings

CNS Depression

Performance of activities requiring mental alertness or physical coordination may be impaired.^{1 2}

Possible additive effect with other CNS depressants and/or alcohol.^{1 2} (See Specific Drugs and Laboratory Tests under Interactions.)

Sensitivity Reactions

Anaphylactic reactions, angioedema, urticaria, pruritus, rash, skin eruptions, and conjunctivitis with nasal congestion have occurred.^{1 2 b}

General Precautions

Seizure Disorders

Although causal relationship not established, seizures reported during IV administration.^b Use injection with caution in patients with known or suspected seizure disorders.²

Specific Populations

Pregnancy

Not known whether the drug can cause fetal harm or affect reproductive capacity.¹ Fetal and congenital abnormalities reported following in utero exposure; animal reproductive studies not conducted.¹ Do not use during pregnancy, particularly during early pregnancy, unless potential benefits outweigh possible risks.¹

Lactation

Distributed into milk in dogs; not known whether distributed into human milk.¹ Use caution.¹

Pediatric Use

Safety and efficacy (other than IV use in the management of tetanus) not established in pediatric patients <16 years of age.^{1 2}

Geriatric Use

Because of risk of injury, skeletal muscle relaxants should generally be avoided in geriatric patients.¹¹¹

Renal Impairment

Polyethylene glycol vehicle of methocarbamol injection may worsen preexisting acidosis and urea retention; although amount present in preparation is well within limits of safety, caution is advised.² Do not administer to patients with impaired renal function.² (See Contraindications under Cautions.)

Common Adverse Effects

Drowsiness, dizziness, lightheadedness.^{1 2 b}

Drug Interactions

Specific Drugs and Laboratory Tests

Methocarbamol Pharmacokinetics

Absorption

Bioavailability

Rapidly and almost completely absorbed following oral administration.²²

Onset

Usually within 30 minutes following oral administration.^b

Almost immediate after IV administration.^b

Distribution

Extent

Widely distributed in dogs, with highest concentrations in the kidney and liver.²⁹

Methocarbamol and/or its metabolites cross the placenta in dogs.²⁹

Distributed into milk in dogs; not known whether distributed into human milk.¹

Plasma Protein Binding

46–50%.¹

Elimination

Metabolism

Extensively metabolized, presumably in the liver, by dealkylation and hydroxylation.^{1 23}

Elimination Route

Eliminated principally in urine as metabolites (40–50% as glucuronide and sulfate conjugates, remainder as unidentified metabolites); small amount (10–15%) eliminated unchanged in urine.^{1 22 23 b} Very small amounts excreted in feces.²³

Half-life

0.9–1.8 hours.^b

Special Populations

In geriatric patients, half-life slightly prolonged.¹

In patients with renal impairment on maintenance dialysis, clearance decreased by 40% but no apparent increase in half-life.¹

In patients with cirrhosis secondary to alcohol abuse, clearance decreased by 70% and half-life increased to about 3.4 hours.¹

Stability

Storage

Oral

Tablets

Tight containers at 20–25°C.¹ Protect from light and moisture.¹⁰²

Parenteral

Injection

20–25°C (may be exposed to 15–30°C).²

Do not refrigerate after dilution.² Precipitation and haze formation may occur if diluted solution is refrigerated.^b Haze formation in diluted solutions may be unpredictable; visually inspect all diluted solutions prior to administration regardless of storage conditions.^b

Compatibility

Parenteral

Solution Compatibility

Actions

• CNS depressant with sedative and skeletal muscle relaxant effects.^{1 2 b}

• Precise mechanism of action is not known; does not directly relax skeletal muscle and has minimal skeletal muscle relaxant effects.^{1 2 b} Beneficial effect probably is related to the drug’s sedative effect.^{1 2 b}

• Unlike neuromuscular blocking agents, does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.^b

Advice to Patients

• Potential to impair mental alertness or physical coordination, especially with concomitant use of alcohol or other CNS depressants; use caution when driving or operating machinery.^{1 2}

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as concomitant illnesses.^{1 2}

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.^{1 2}

• Importance of informing patients of other important precautionary information.^{1 2} (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

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