Generic Name: methocarbamol

Brand Names: Carbacot, Skelex, Robaxin, Robaxin-750

Uses

Muscular Conditions

Adjunct to rest, physical therapy, analgesics, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.

For low back pain, generally reserve skeletal muscle relaxants for adjunctive treatment when pain is unresponsive to OTC analgesics (e.g., NSAIAs).

Skeletal muscle relaxants less well tolerated than NSAIAs, and clinical superiority to NSAIAs not established for low back pain.

Various skeletal muscle relaxants appear to have comparable efficacy for low back pain relief and are more effective than placebo.

Initially, symptomatic control of acute low back pain focuses on providing sufficient comfort to allow maximum possible activity while awaiting spontaneous recovery; later, as aid to overcome specific activity intolerance.

Because of rapid spontaneous recovery rate, efficacy of various therapies may be difficult to establish; improvement of low back pain usually occurs within 2 weeks, substantial improvement within 4 weeks.

Ineffective in the treatment of skeletal muscle hyperactivity secondary to chronic neurologic disorders (e.g., cerebral palsy) and other dyskinesias.

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. However, most authorities prefer other sedatives or muscle relaxants (e.g., diazepam) and, in severe cases, neuromuscular blocking agents.

Dosage and Administration

Administration

Administer orally; may administer IV or IM when oral administration is not feasible or for severe musculoskeletal pain. Do not administer sub-Q.

Switch from parenteral to oral therapy as soon as possible.

Oral Administration

NG Tube

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

IV Administration

For solution compatibility information, see Compatibility under Stability.

Administer by direct IV injection or by IV infusion.

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

Avoid extravasation; solution is hypertonic.

For direct IV use, inject undiluted solution slowly to minimize adverse effects.

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.

Dilution

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

Visually inspect diluted solutions for haze prior to administration. (See Stability.)

Rate of Administration

For direct IV injection, maximum rate of 300 mg (3 mL of 10% injection) per minute. Some clinicians have recommended injection at rate of 180 mg/m² per minute in children.

IM Administration

Administer no more than 500 mg (5 mL of 10% injection) into each gluteal region.

Dosage

Pediatric Patients

Tetanus

IV

Children ≥12 years of age: Recommended minimum initial dose is 15 mg/kg or 500 mg/m²; 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).

Adults

Muscular Conditions

Oral

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

A few patients may require initial dosage of 8 g daily in divided doses.

IV or IM

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

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

Tetanus

IV, then Oral

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

Repeat IV infusion of 1–2 g every 6 hours until NG tube can be inserted. Up to 24 g daily (via NG tube) may be required.

Prescribing Limits

Pediatric Patients

Tetanus

IV

Maximum 1.8 g/m² daily for 3 consecutive days.

Adults

Muscular Conditions

IV or IM

Maximum 3 g daily for 3 consecutive days.

Cautions

Contraindications

• Injection contraindicated in patients with impaired renal function. (See Renal Impairment under Cautions.)
• Known hypersensitivity to methocarbamol or any ingredient in the formulation.

Warnings/Precautions

Warnings

CNS Depression

Performance of activities requiring mental alertness or physical coordination may be impaired.

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

Sensitivity Reactions

Anaphylactic reactions, urticaria, pruritus, rash, skin eruptions, and conjunctivitis with nasal congestion have occurred.

Latex Sensitivity

The stopper of the methocarbamol injection (Robaxin^®) vial contains dry natural rubber (latex). Some individuals may be hypersensitive to natural latex proteins. Take appropriate precautions if injection is handled by or administered to individuals with a history of latex sensitivity.

General Precautions

Epilepsy

Use IV or IM with caution, if at all, in patients with known or suspected epilepsy.

Specific Populations

Pregnancy

Category C.

Lactation

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

Pediatric Use

Safety and efficacy (other than IV use in the management of tetanus) not established in children.

Renal Impairment

Polyethylene glycol vehicle of methocarbamol injection may be irritating to the kidneys; may worsen preexisting acidosis and urea retention. Do not administer to patients with impaired renal function.

Common Adverse Effects

Drowsiness, dizziness, lightheadedness.

Interactions

Specific Drugs and Laboratory Tests

Pharmacokinetics

Absorption

Bioavailability

Rapidly and almost completely absorbed following oral administration.

Onset

Usually within 30 minutes following oral administration.

Almost immediate after IV administration.

Distribution

Extent

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

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

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

Plasma Protein Binding

46–50%.

Elimination

Metabolism

Extensively metabolized, presumably in the liver, by dealkylation and hydroxylation.

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. Very small amounts excreted in feces.

Half-life

0.9–1.8 hours.

Special Populations

In geriatric patients, half-life slightly prolonged.

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

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

Stability

Storage

Oral

Tablets

Tight containers at 20–25°C.

Parenteral

Injection

20–25°C (may be exposed to 15–30°C). Do not freeze.

Do not refrigerate after dilution (see Compatibility under Stability).

Compatibility

For information on systemic interactions resulting from concomitant use, see Interactions.

Parenteral

Precipitation and haze formation may occur if diluted solution is refrigerated.

Haze formation in diluted solutions may be unpredictable; visually inspect all diluted solutions prior to administration regardless of storage conditions.

Solution Compatibility

Actions

• CNS depressant with sedative and skeletal muscle relaxant effects.
• Precise mechanism of action is not known; does not directly relax skeletal muscle and has minimal skeletal muscle relaxant effects. Beneficial effect probably is related to the drug’s sedative effect.
• Unlike neuromuscular blocking agents, does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.

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.
• 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.
• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.
• Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

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

Comparative Pricing

This pricing information is subject to change at the sole discretion of DS Pharmacy. This pricing information was updated 09/2009. For the most current and up-to-date pricing information, please visit www.drugstore.com. Actual costs to patients will vary depending on the use of specific retail or mail-order locations and health insurance copays.

AHFS Drug Information. © Copyright, 1959-2009, Selected Revisions April 2007. American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland 20814.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.