Methocarbamol

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DRUGS
Methocarbamol

Methocarbamol belongs to class of centrally acting “muscle relaxant”. It is used to treat muscle pain and stiffness. It is generally used with rest and physical therapy for the treatment of muscle pain and stiffness.

Introduction

Methocarbamol belongs to class of centrally acting “muscle relaxant”. It is used to treat muscle pain and stiffness. It is generally used with rest and physical therapy for the treatment of muscle pain and stiffness.

Pharmacological class: Muscle relaxant

Indications

  • Muscle pain and stiffness

Pharamcological Action

Methocarbamol is a central muscle relaxant for skeletal muscles, used to treat spasms. It is structurally related to guaifenesin. The exact mechanism of methocarbamol causing skeletal muscle relaxation is unknown. It is thought to work centrally, perhaps by general depressant effects. It has no direct relaxant effects on striated muscle, nerve fibers, or the motor endplate. It will not directly relax contracted skeletal muscles. The drug has a secondary sedative effect.

Dosage

Usual Adult Dose for Muscle Spasm

Oral:

Initial dose: 1500 mg four times a day for the first 48 to 72 hours, up to a maximum dosage of 8 g/day for severe symptoms.

Maintenance dose: 4000 to 4500 mg/day in divided doses.

IV or IM:

1000 mg up to every 8 hours if necessary, not to exceed 3 g/day for more than 3 consecutive days except in the treatment of tetanus. 

Pharmacokinetics

The plasma clearance of methocarbamol ranges between 0.20 and 0.80 L/h/kg, the mean plasma elimination half-life ranges between 1 and 2 hours, and the plasma protein binding ranges between 46% and 50%. Methocarbamol is metabolized via dealkylation and hydroxylation. Conjugation of methocarbamol also is likely. Essentially all methocarbamol metabolites are eliminated in the urine. Small amounts of unchanged methocarbamol also are excreted in the urine.

Contraindications

  • Contraindicated in patients with liver problems

  • Contraindicated in patients with kidney diseases

  • Contraindicated in patients receiving other CNS depressants, alcohol or psychotropic drugs

  • Contraindicated in patients with known hypersensitivity to methocarbamol

  • Contraindicated in patients with seizure disorders

Drug Interactions

  • Methocarbamol may inhibit the effect of pyridostigmine bromide. Therefore, methocarbamol should be used with caution in patients with myasthenia gravis receiving anticholinesterase agents.

  • Methocarbamol may cause a color interference in certain screening tests for 5-hydroxyindoleacetic acid (5-HIAA) using nitrosonaphthol reagent and in screening tests for urinary vanillylmandelic acid (VMA) using the Gitlow method.

  • Concomitant use of methocarbamol with carbinoxamine may increase the risk of CNS depression and psychomotor impairment.

Side effects

Common (affecting between 1 in10 to 1 in 100)

  • Eyesight problem

  • Injection site signs and symptoms

  • Blurred vision

  • Dizziness

  • Double vision

  • Drowsiness

Uncommon (affecting 1 in 100 to 1 in 1000)

  • Fever caused by drug administration

  • Hives

  • Skin inflammation caused by allergy

  • Itching

  • Pink eye

  • Rash

  • Slow heartbeat

  • Stuffy nose

  • Feel like throwing up

  • Head pain

  • Indigestion

  • Involuntary eye movement

  • Muscle weakness

  • Temporary redness of face and neck

Very rare (affecting less than 1 in 10,000)

  • Abnormally low blood pressure

  • Blood clot in vein

  • Confused

  • Decreased white blood cells

  • Dyskinesia

  • Feeling faint

  • Life threatening allergic reaction

  • Yellowing of skin/eyes from bile flow and liver problems

  • Chronic trouble sleeping

  • Inducing of a relaxed easy state

  • Loss of memory

  • Sensation of spinning or whirling

Precautions

  • Special precaution is to be taken for the patients hypersensitive to latex.

  • Special precaution is to be taken if concurrent CNS depressant use is advised.

  • Special precaution is to be taken for alcohol users.

  • Special precaution is to be taken for elderly patients.

Clinic Evidence

In a randomized, placebo controlled multi-centre study, inclusion criteria were acute low back pain for at least 24 h associated with spasms in the pelvic/lumbar region and restriction of mobility. Patients were randomly assigned to a group treated with orally administered methocarbamol (n = 98) or placebo (n = 104). Individual pain perception was quantified by means of a visual analog scale (VAS). The fingertip-to-floor distance was measured as an indicator of lumbar flexion. Mobility restrictions were also assessed by a modified Schober's test. In addition, a questionnaire was used by patients and physicians to rate the efficacy of treatment. In methocarbamol group 44% of the patients pre-terminated due to complete pain relief (placebo: 18%) and 19% discontinued because the treatment was considered ineffective (placebo 52%, p < 0,0001). Measures of mobility and improvement of mobility as perceived by physician and patient at the individual end of study all were clearly in favor of the patients treated with methocarbamol. At the final visit, 67% of the patients who had received methocarbamol (35% placebo patients) and 70% of their physicians (control group: 36%) considered the treatment to be effective. No severe adverse effects were observed during the study. This study showed that methocarbamol, orally administered, is an efficient and well-tolerated therapeutic option for patients suffering from acute LBP and the typically associated restrictions of mobility.1

References

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