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Methocarbamol

Pronunciation

Pronunciation: meth-oh-CAR-buh-mahl
Class: Skeletal muscle relaxant, centrally acting

Trade Names

Robaxin
- Tablets 500 mg
- Injection 100 mg/mL

Robaxin-750
- Tablets 750 mg

Pharmacology

May cause relaxation of skeletal muscle via general CNS depression. Does not directly relax tense skeletal muscles.

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Pharmacokinetics

Absorption

T max is 2 h.

Distribution

Methocarbamol protein binding is 46% to 50%.

Elimination

Inactive metabolites are excreted in urine and small amounts in feces. The t ½ is 1 to 2 h.

Onset

Onset is 30 min.

Special Populations

Renal Function Impairment

Cl is decreased approximately 40% in patients with severe renal impairment.

Hepatic Function Impairment

Cl is decreased approximately 70%; t 1/ 2 is prolonged to approximately 3.4 h in cirrhosis patients.

Children

Safety and efficacy in children younger than 16 yr of age not established, except in tetanus.

Indications and Usage

Adjunctive therapy for relief of painful, acute musculoskeletal conditions; control of neuromuscular manifestations of tetanus.

Contraindications

Renal pathologic disorders (parenteral form); standard considerations.

Dosage and Administration

Skeletal Muscle Relaxation
Adults Initial dose

IV/IM 3 g over no more than 3 consecutive days. Repeat course after 48-h lapse if condition persists. PO 1.5 g 4 times daily.

Maintenance

PO 1 g 4 times daily, 750 mg every 4 h, or 1.5 g 3 times daily. For first 48 to 72 h, 6 to 8 g/day is recommended; then reduce to 4 g/day.

Tetanus
Adults

IV 1 to 2 g; additional 1 to 2 g may be added to infusion up to 3 g total. Repeat every 6 h until oral form may be administered.

Children

IV/IV infusion 15 mg/kg initially; then 15 mg/kg every 6 h.

General Advice

  • Injection
  • For IV or IM administration only. Not for intradermal, subcutaneous, or intra-arterial administration.
  • Administer direct IV injection of undiluted methocarbamol at max rate of 3 mL/min.
  • For IV infusion dilute prescribed dose in no more than 250 mL of sodium chloride injection or 5% dextrose injection.
  • Use diluted solution as soon as possible. Do not refrigerate diluted solution for IV administration.
  • Administer prescribed IM dose by deep, slow injection into gluteal region. Do not inject more than 5 mL at 1 site. Rotate injection sites.
  • Do not administer injection if particulate matter, cloudiness, or discoloration noted.

Storage/Stability

Store at controlled room temperature (68° to 77°F).

Drug Interactions

Alcohol, CNS depressants

CNS depressant effects may be additive.

Anticholinesterase agents (eg, pyridostigmine)

Because effects may be inhibited by methocarbamol, use with caution in patients with myasthenia gravis who are receiving anticholinergic agents.

Laboratory Test Interactions

Screening tests for 5-hydroxy-indoleacetic acid or vanillylmandelic acid

Drug may cause color interference.

Adverse Reactions

Cardiovascular

Bradycardia; hypotension; syncope; thrombophlebitis.

CNS

Headache; amnesia; confusion; dizziness/lightheadedness; drowsiness; insomnia; mild muscular incoordination; sedation; seizures (including grand mal); vertigo.

Dermatologic

Flushing; pruritus; rash; urticaria.

EENT

Diplopia; nystagmus; blurred vision; conjunctivitis; nasal congestion.

GI

Dyspepsia; nausea; vomiting; metallic taste.

Hematologic

Leukopenia.

Hepatic

Jaundice (including cholestatic jaundice).

Miscellaneous

Hypersensitivity reactions, anaphylactic reactions; angioneurotic edema; fever.

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy in children younger than 16 yr of age not established, except for management of tetanus.

Overdosage

Symptoms

Frequently occurs in conjunction with alcohol or other CNS depressants and includes nausea, drowsiness, blurred vision, hypotension, seizures, and coma.

Patient Information

  • Advise patient or caregiver that injectable medication will be prepared and administered by a health care provider in a medical setting.
  • Advise patient that medication will be most effective when combined with rest and prescribed physical therapy.
  • Advise patient that dose may be adjusted periodically in order to achieve max benefit.
  • Advise patient to take prescribed dose as needed for muscle spasm or limited mobility.
  • Advise patient to take without regard to meals but to take with food if stomach upset occurs.
  • Instruct patient to avoid alcoholic beverages and sedatives (eg, diazepam) while taking methocarbamol.
  • Advise patient that medication may cause urine to turn a dark brown, black, or green and not to be concerned; this is expected and not harmful.
  • Advise patient that drug may cause drowsiness or dizziness and to use caution while driving or performing other tasks requiring mental alertness until tolerance is determined.
  • Advise patient to stop taking and notify health care provider if any of the following occur: allergic reaction, persistent dizziness, excessive sedation.

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