General

Pronunciation
meth-oh-KAR-ba-mole

Trade Name(s)

• Carbacot

• Robaxin

Pregnancy Category
Category C

Ther. class.
skeletal muscle relaxants
(centrally acting)

Indications

Adjunctive treatment of muscle spasm associated with acute painful musculoskeletal conditions (with rest and physical therapy)

Action

Skeletal muscle relaxation, probably as a result of CNS depression

Therapeutic Effect(s):
Skeletal muscle relaxation

Pharmacokinetics

Absorption: Rapidly absorbed from the GI tract

Distribution: Widely distributed. Crosses the placenta; enters breast milk in small amounts

Metabolism and Excretion: Metabolized by the liver

Half-life: 1–2 hr

TIME/ACTION PROFILE (skeletal muscle relaxation)

ROUTE	ONSET	PEAK	DURATION
PO	30 min	2 hr	unknown
IM	rapid	unknown	unknown
IV	immediate	end of infusion	unknown

Contraindication/Precautions

Contraindicated in:

• Hypersensitivity

• Hypersensitivity to polyethylene glycol (parenteral only)

• Renal impairment (parenteral form)

Use Cautiously in:

• Pregnancy, lactation, and children (safety not established)

• Geri: Appears on Beers list. Poorly tolerated due to anticholinergic effects

• Seizure disorders (parenteral form)

Adverse Reactions/Side Effects

CNS: SEIZURES (IV, IM ONLY), dizziness, drowsiness, light-headedness.

EENT: blurred vision, nasal congestion.

CV: IV—bradycardia, hypotension.

GI: anorexia, GI upset, nausea.

GU: brown, black, or green urine.

Derm: flushing (IV only), pruritus, rashes, urticaria.

Local: pain at IM site, phlebitis at IV site.

Misc: ALLERGIC REACTIONS INCLUDING ANAPHYLAXIS (IM, IV USE ONLY), fever.

*CAPITALS indicates life-threatening.
*italic indicates most frequent.

Interactions

Drug-Drug
Additive CNS depression with other CNS depressants, including alcohol, antihistamines, opioid analgesics, and sedative/hypnotics

Drug-Natural Products
Concomitant use of kava, valerian, chamomile, or hops can CNS depression

Route/Dosage

• PO (Adults): 1.5 g qid initially (up to 8 g/day) for 2–3 days, then 4–4.5 g/day in 3–6 divided doses; may be followed by maintenance dosing of 750 mg q 4 hr or 1 g 4 times daily or 1.5 g 3 times daily.

• IM, IV (Adults): 1–3 g/day for not more than 3 days; course may be repeated after a 48-hr rest.

Availability

• Tablets: 500 mg, 750 mg

• Injection: 100 mg/ml in 10-ml ampules[canada], 100 mg/ml in 10-ml vials

• In combination with: aspirin (Robaxisal). See combination drugs

Assessment

• Assess patient for pain, muscle stiffness, and range of motion before and periodically throughout therapy

• Monitor pulse and blood pressure every 15 min during parenteral administration

• Geri: Assess geriatric patients for anticholinergic effects (sedation and weakness)

• Assess patient for allergic reactions (skin rash, asthma, hives, wheezing, hypotension) after parenteral administration. Keep epinephrine and oxygen on hand in the event of a reaction

• Monitor IV site. Injection is hypertonic and may cause thrombophlebitis. Avoid extravasation

Lab Test Considerations

• Monitor renal function periodically during prolonged parenteral therapy (>3 days), because polyethylene glycol 300 vehicle is nephrotoxic

» May cause falsely increased urinary 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA) determinations

Potential Nursing Diagnoses

• Acute pain (Indications)

• Impaired physical mobility (Indications)

• Risk for injury (Side Effects)

Implementation

• Provide safety measures as indicated. Supervise ambulation and transfer of patients

• PO: May be administered with food to minimize GI irritation. Tablets may be crushed and mixed with food or liquids to facilitate swallowing. For administration via NG tube, crush tablet and suspend in water or saline

• IM: Do not administer subcut. IM injections should contain no more than 5 ml (500 mg) at a time in the gluteal region

IV Adminstration:

• Direct IV:
Diluent: Administer undiluted

• Concentration:
100 mg/ml.

• Rate:
Administer at a maximum rate of 180 mg/m2/min but not > 3 ml (300 mg)/min

• Intermittent Infusion:
Diluent: Dilute each dose in no more than 250 ml of 0.9% NaCl or D5W for injection.
Concentration: 4 mg/ml for slower infusions.Do not refrigerate after dilution
Have patient remain recumbent during and for at least 10–15 min after infusion to avoid orthostatic hypotension

Patient/Family Teaching

• Advise patient to take medication as directed. Take missed doses within 1 hr; if not, return to regular dosing schedule. Do not double doses

• Encourage patient to comply with additional therapies prescribed for muscle spasm (rest, physical therapy, heat)

• May cause dizziness, drowsiness, and blurred vision. Advise patient to avoid driving and other activities requiring alertness until response to drug is known

• Instruct patient to change positions slowly to minimize orthostatic hypotension

• Advise patient to avoid concurrent use of alcohol and other CNS depressants

• Inform patient that urine may turn black, brown, or green, especially if left standing

• Instruct patient to notify health care professional if skin rash, itching, fever, or nasal congestion occurs

• Emphasize the importance of routine follow-up exams to monitor progress

Evaluation/Desired Outcomes

Decreased musculoskeletal pain and muscle spasticity

» Increased range of motion

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