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Methocarbamol (Robaxin)


Methocarbamol 750
  • Generic name: Methocarbamol
  • Trade names: Robaxin®, Robaxin®-750
  • Drug class: Skeletal Muscle Relaxant, Antispasmodic
  • Dosages: 500 mg, 750 mg tablets
  • Pregnancy category: C

Methocarbamol, a guaifenesin derivative, is a centrally acting muscle relaxant (spasmolytic). It is used as adjunct to rest and physical therapy for the relief of discomfort associated with acute, painful musculoskeletal conditions (e.g. low back pain, neck pain, trauma, strain). Methocarbamol is also used to alleviate symptoms of tetanus.

  • Onset of action: within 30 minutes
  • Duration of action: 24 hours

Is Methocarbamol addictive?

Methocarbamol, at doses greatly above those used therapeutically, has some potential for abuse by persons with histories of drug abuse. However, this potential for abuse or addiction is probably decreased by the accompanying side effects at high doses [2].

Is Methocarbamol stronger than Carisoprodol (Soma)?

They are completely different medications, though do the same job.

Carisoprodol is considered to be the stronger of the two medications. However, with more strength come more side effects. Carisoprodol is a controlled substance -- it is more dangerous and addictive than other muscle relaxers.

The only head to head comparison of carisoprodol vs methocarbamol was in patients with chronic leg pain [3]. Carisoprodol was superior to methocarbamol for the relief of chronic moderate- to-severe pain.

Dosage

The recommended starting methocarbamol dosage is 1500 mg (two 750 mg tablets) 4 times daily for 2–3 days. Then, the dose should be reduced to 750 mg 4-6 times daily.

Drug interactions

  • Alcohol, CNS depressants: additive CNS depressant effects.
  • Pyridostigmine: diminished therapeutic effect of pyridostigmine.

Side effects

  • Cardiovascular: bradycardia, flushing, hypotension, syncope
  • Gastrointestinal: dyspepsia, metallic taste, nausea, vomiting, jaundice (including cholestatic jaundice)
  • Hematologic: leukopenia
  • Immune system: hypersensitivity reactions including anaphylaxis
  • Nervous system: amnesia, confusion, coordination impaired (mild), dizziness, drowsiness, headache, insomnia, lightheadedness, sedation, seizures, vertigo
  • Ocular: blurred vision, conjunctivitis, diplopia, nystagmus
  • Skin: angioneurotic edema, pruritus, rash, urticaria

Mechanism of Action

The mode of action of methocarbamol may be related to its sedative properties. It has no direct relaxant effects on tense skeletal muscles, nerve fibers, or the motor endplate.

Methocarbamol is less sedating than tizanidine (Zanaflex) and cyclobenzaprine (Flexeril).

Contraindications

  • Hypersensitivity
  • Impaired renal function (for IM)

References:

  • 1. Methocarbamol National Library of Medicine.
  • 2. Preston KL, Guarino JJ, Kirk WT, Griffiths RR. Evaluation of the abuse potential of methocarbamol. J Pharmacol Exp Ther. 1989 Mar;248(3):1146-57.
  • 3. Stern FH. A controlled comparison of three muscle relaxant agents. Clin Med 1964; 71:367-72.

Last Updated: March 02, 2013

Interesting facts
  • Methocarbamol was approved for use in the United States in 1957.
  • It has a relatively low likelihood of abuse.
  • Methocarbamol is structurally related to mephenesin, an older muscle relaxant that is no longer used because it was associated with blood clots and other dangerous effects.
  • Methocarbamol similar to guaifenesin -- it is a carbamate of guaifenesin, but is NOT metabolized to guaifenesin.


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