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1. causing relaxation.
2. an agent that causes relaxation.
muscle relaxant an agent that specifically aids in reducing muscle tension.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


PMS-Methocarbamol (CA), Robaxin

Pharmacologic class: Autonomic nervous system agent

Therapeutic class: Skeletal muscle relaxant (centrally acting)

Pregnancy risk category C


Unknown. Thought to depress central perception of pain without directly relaxing skeletal muscles or directly affecting motor endplate or motor nerves.


Injection: 100 mg/ml in 10-ml ampules, 100 mg/ml in 10-ml vials

Tablets: 500 mg, 750 mg

Indications and dosages

Adjunct in muscle spasms caused by acute, painful musculoskeletal conditions

Adults: Initially, 1.5 g P.O. q.i.d. (up to 8 g/day) for 2 to 3 days, then 4 to 4.5 g/day P.O. in three to six divided doses; or 750 mg P.O. q 4 hours or 1 g P.O. q.i.d. or 1.5 g P.O. t.i.d. If oral dosing isn't feasible or if condition is severe, give 1 to 3 g/day I.M. or I.V. for maximum of 3 days.

Off-label uses

• Tetanus


• Hypersensitivity to drug, its components, or polyethylene glycol (with parenteral form)

• Renal impairment (with parenteral form)


Use cautiously in:

• seizure disorders (with parenteral use)

• pregnant or breastfeeding patients

• children (safety not established).


• For direct I.V. injection, administer slowly. Keep patient supine for 10 to 15 minutes afterward.

• For I.V. infusion, dilute 1 g with up to 250 ml 5% dextrose or 0.9% sodium chloride injection.

• Avoid extravasation; drug is hypertonic.

• Don't give subcutaneously.

• For I.M. use, inject no more than 500 mg (5 ml of 10% injection) into each gluteal area.

• Don't use parenteral form in patients with renal impairment. Polyethylene glycol vehicle may irritate kidneys.

• When giving for tetanus, crush and suspend tablets in water or saline solution, and give via nasogastric tube, if necessary.

• Be aware that drug is usually given as part of regimen that includes rest and physical therapy.

Adverse reactions

CNS: dizziness, light-headedness, drowsiness, syncope, seizures (with I.V. use)

CV: bradycardia or hypotension (with I.V. use)

EENT: blurred vision, conjunctivitis, nasal congestion

GI: nausea, GI upset, anorexia

GU: brown, black, or green urine

Musculoskeletal: mild muscle incoordination (with I.V. or I.M. use)

Skin: flushing (with I.V. use), pruritus, rash, urticaria

Other: fever, pain at I.M. injection site, phlebitis at I.V. site, allergic reactions including anaphylaxis (with I.M. or I.V. use)


Drug-drug. Antihistamines, CNS depressants (such as opioids, sedative-hypnotics): additive CNS depression

Drug-diagnostic tests. Urinary 5-hydroxyindoleacetic acid, urine vanillylmandelic acid: false elevations

Drug-herbs. Chamomile, hops, kava, skullcap, valerian: increased CNS depression

Drug-behaviors. Alcohol use: increased CNS depression

Patient monitoring

• Assess for orthostatic hypotension, especially with parenteral use. Keep patient supine for 10 to 15 minutes after I.V. administration.

Watch for anaphylaxis after I.M. or I.V. administration.

Stay alert for bradycardia and syncope after I.V. or I.M. dose. As needed and prescribed, give epinephrine, corticosteroids, or antihistamines.

• Monitor I.V. site frequently to prevent sloughing and thrombophlebitis.

Patient teaching

• Tell patient that drug may turn urine brown, black, or green.

• Caution patient to avoid driving and other hazardous activities, because drug may cause drowsiness or dizziness.

• Instruct patient to move slowly when changing position, to avoid dizziness from sudden blood pressure decrease.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


A drug that is a central nervous system depressant and is used for the relief of discomfort associated with painful musculoskeletal conditions.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A centrally-acting muscle relaxant drug used to treat conditions of severe muscle spasm. A brand name is Robaxin.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005