Methocarbamol

Pronunciation

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
Brands: Robaxin

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.a b c

If pharmacologic therapy is required for acute low back pain (usually a benign and self-limiting condition105 106 108 ), an analgesic (e.g., acetaminophen, NSAIA) generally is recommended.104 105 106 108 117 Skeletal muscle relaxants may be used alone or in combination with analgesics for short-term relief; however, consider high incidence of adverse effects (e.g., CNS effects).104 106 107 108 Use skeletal muscle relaxants with caution and weigh risks against benefits.104 106 107 108

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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.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.a b c Do not administer sub-Q.b

Switch from parenteral to oral therapy as soon as possible.b

Oral Administration

NG Tube

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

IV Administration

For solution compatibility information, see Compatibility under Stability.

Administer by direct IV injection or by IV infusion.b c

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

Avoid extravasation; solution is hypertonic.b c

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

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.b c

Dilution

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

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

Rate of Administration

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

IM Administration

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

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).b c

Adults

Muscular Conditions
Oral

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

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

IV or IM

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

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

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).b c

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

Prescribing Limits

Pediatric Patients

Tetanus
IV

Maximum 1.8 g/m2 daily for 3 consecutive days.b c

Adults

Muscular Conditions
IV or IM

Maximum 3 g daily for 3 consecutive days.b c

Cautions for Methocarbamol

Contraindications

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

  • Known hypersensitivity to methocarbamol or any ingredient in the formulation.a b c

Warnings/Precautions

Warnings

CNS Depression

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

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

Sensitivity Reactions

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

Latex Sensitivity

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

General Precautions

Epilepsy

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

Specific Populations

Pregnancy

Category C.a b c

Lactation

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

Pediatric Use

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

Renal Impairment

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

Common Adverse Effects

Drowsiness, dizziness, lightheadedness.a b c

Interactions for Methocarbamol

Specific Drugs and Laboratory Tests

Drug or Test

Interaction

Comments

Anticholinesterase agents (e.g., pyridostigmine)

Potential for severe weaknessa b c

Use with caution in patients with myasthenia gravisa b c

CNS depressants (e.g., alcohol)

Potential for additive CNS depressiona b c

Use caution to avoid overdosagea b c

Tests for 5-hydroxyindolacetic acid (5-HIAA) in urine (nitrosonaphthol reagent in quantitative method of Udenfriend)

False-positive results (color interference) a b c

Tests for vanillylmandelic acid (VMA) in urine by the screening method of Gitlow

False-positive results (color interference)a b c

Methocarbamol Pharmacokinetics

Absorption

Bioavailability

Rapidly and almost completely absorbed following oral administration.b

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.b

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

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

Plasma Protein Binding

46–50%.a c

Elimination

Metabolism

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

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.b Very small amounts excreted in feces.b

Half-life

0.9–1.8 hours.b

Special Populations

In geriatric patients, half-life slightly prolonged.a c

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

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

Stability

Storage

Oral

Tablets

Tight containers at 20–25°C.a

Parenteral

Injection

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

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

Compatibility

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

Parenteral

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

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

Solution Compatibility

Compatible

Dextrose 5% in waterc

Sodium chloride 0.9%c

Actions

  • CNS depressant with sedative and skeletal muscle relaxant effects.a b c

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

  • 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.a b c

  • 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.a b c

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.a b

  • 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.

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

Methocarbamol

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Tablets

500 mg*

Methocarbamol Tablets

750 mg*

Methocarbamol Tablets

Tablets, film-coated

500 mg

Robaxin

Schwarz

750 mg

Robaxin

Schwarz

Parenteral

Injection

100 mg/mL

Robaxin

Baxter

Comparative Pricing

This pricing information is subject to change at the sole discretion of DS Pharmacy. This pricing information was updated 02/2014. Actual costs to patients will vary depending on the use of specific retail or mail-order locations and health insurance copays.

Methocarbamol 500MG Tablets (WEST-WARD): 60/$15.99 or 120/$24.97

Methocarbamol 750MG Tablets (WEST-WARD): 30/$14.99 or 90/$24.97

Robaxin 500MG Tablets (ACTIENT PHARMACEUTICALS): 30/$65.40 or 90/$163.51

Robaxin-750 750MG Tablets (ACTIENT PHARMACEUTICALS): 30/$82.83 or 90/$219.08

AHFS DI Essentials. © Copyright, 2004-2014, Selected Revisions November 18, 2012. American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland 20814.

References

103. See S, Ginzburg R. Skeletal muscle relaxants. Pharmacotherapy. 2008; 28:207-13. [PubMed 18225966]

104. van Tulder MW, Touray T, Furlan AD et al. Muscle relaxants for non-specific low back pain. Cochrane Database Syst Rev. 2003; :CD004252. [PubMed 12804507]

105. Roelofs PD, Deyo RA, Koes BW et al. Non-steroidal anti-inflammatory drugs for low back pain. Cochrane Database Syst Rev. 2008; :CD000396. [PubMed 18253976]

106. Chou R, Qaseem A, Snow V et al. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med. 2007; 147:478-91. [PubMed 17909209]

107. Institute for Clinical Systems Improvement. Health care guideline: adult acute and subacute low back pain. 15th ed. Bloomington, MN; 2012 Jan. From the ICSI website

108. Toth PP, Urtis J. Commonly used muscle relaxant therapies for acute low back pain: a review of carisoprodol, cyclobenzaprine hydrochloride, and metaxalone. Clin Ther. 2004; 26:1355-67. [PubMed 15530999]

117. Boothby LA, Doering PL, Hatton RC. Carisoprodol: a marginally effective skeletal muscle relaxant with serious abuse potential. Hosp Pharm. 2003; 38:337-45.

a. Schwarz Pharma. Robaxin and Robaxin-750 tablets prescribing information. Milwaukee, WI; 2003 Apr.

b. AHFS Drug Information 2004. McEvoy GK, ed. Methocarbamol. Bethesda, MD: American Society of Health-System Pharmacists; 2004: 1336-7.

c. Baxter. Robaxin injection prescribing information. Deerfield, IL; 2003 Nov.

d. Food and Drug Administration. Amended economic impact analysis of final rule requiring use of labeling on natural rubber containing devices. 21 CFR Part 801. Final rule. (Docket No. 96N-0119) Fed Regist. 1998; 63:50660-704.

e. Food and Drug Administration. Latex-containing devices; user labeling. 21 CFR Part 801. Proposed rule. (Docket No. 96N-0119) Fed Regist. 1996; 61:32617-21.

f. Food and Drug Administration. Natural rubber-containing medical devices; user labeling. 21 CFR Part 801. Final rule. (Docket No. 96N-0119) Fed Regist. 1997; 62:51021-30.

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