Metocarbamol: Formula, Presentation, Indications, Mechanism of Action, Dosage, Side Effects and Interactions

It is used in the treatment of musculoskeletal conditions related to muscle pain.

Methocarbamol is a centrally acting muscle relaxant used as a supplement, which indicates rest, physiotherapy, and other measures to relieve discomfort.

Chemical formula

  • C11H15NO5.


  • Oral administration tablets of 500 mg and 750 mg.


A muscle relaxant is also indicated for treating neuromuscular manifestations of tetanus, although it has now been replaced in the treatment of tetanus by Diazepam.

In severe cases, it has been replaced by a neuromuscular blocking agent such as pancuronium.

This therapy complements other measures, such as debridement, tetanus antitoxin, penicillin, tracheotomy, fluid and electrolyte replacement, and support treatment.

Thus, methocarbamol has its clinical and therapeutic uses mainly in treating muscle spasms and immobility related to strains, sprains, and back injuries, also in neck injuries, to a lesser degree.

They have also been used to treat a wide variety of clinical conditions common for skeletal muscle hyperactivity, such as muscle spasms that can occur in cases of multiple sclerosis.


Mechanism of action

The mechanism of action of Methocarbamol is not known precisely; it is believed that it may be related to its sedative and relaxing effects as a central nervous system depressant.

The relaxing effects in the skeletal muscle of methocarbamol administered orally and parenterally are minimal.

This drug does not directly relate to skeletal muscle; unlike neuromuscular blocking agents, it does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.

Instead of acting directly on the skeletal muscle, these agents work on the central nervous system.

It has been shown that several of these drugs depress polysynaptic reflexes preferentially.

So the muscle relaxant effects of most of these agents may be related to the depressant effects of the drug in the central nervous system.

Methocarbamol is a central muscle relaxant for skeletal muscles, structurally related to guaifenesin, causes muscle relaxation, and is thought to work centrally, perhaps due to general depressant effects.

Methocarbamol has no direct relaxing effects on skeletal muscle, nerve fibers, or the motor endplate and does not directly relax the contracted skeletal muscles.


The recommended doses are:

  • Methocarbamol, 500 mg: in adults, treatment should be started with three tablets and a maintenance dose of two pills every six hours.
  • Methocarbamol, 750 mg: in adults, it should be activated with two tablets every six hours and a maintenance dose of one tablet every four hours or two tablets every eight hours.

Side effects

The side effects that occur most frequently and that are coincident with the administration of methocarbamol include:

  • The body has been reported anaphylactic reactions, angioneurotic edema, fever, and headache.
  • After administering the drug, it can also occur at the level of the cardiovascular system effects such as bradycardia, hot flashes, flushing, low levels of blood pressure, syncope, and thrombophlebitis.
  • In the digestive system have been reported the occurrence of dyspepsia, gastrointestinal disorders, and jaundice, including cholestatic jaundice, nausea, and vomiting have also been reported.
  • Anorexia and adynamic ileus have also been reported.
  • Reactions such as leukopenia have been observed at the blood and lymphatic system level.
  • Hypersensitivity reactions have been observed in the immune system.
  • Symptoms such as Amnesia, confusion, diplopia, dizziness or dizziness, drowsiness, insomnia, lack of mild muscle coordination, nystagmus, sedation effects, seizures, and vertigo, have been presented to the level of the nervous system.
  • Blurred vision has been observed on the skin and special senses, diplopia, conjunctivitis, nasal congestion, metallic taste, pruritus, skin rash, and urticaria.

Warnings and contraindications

It should not be administered in allergy to the drug and is contraindicated in patients with hypersensitivity to its components.

Allergic reactions such as hives, pruritus, rash, rashes, and conjunctivitis with nasal congestion may occur in methocarbamol patients.

Anaphylactic reactions have occurred after intramuscular or intravenous administration of the drug.

Although most patients with syncope induced by methocarbamol recover with supportive treatment, epinephrine, corticosteroids, and antihistamines have been used to increase the rate of recovery in some of these patients.

When intravenous methocarbamol is administered, thrombophlebitis and pain at the injection site occur, which may result from extravasation.

The intramuscular application of the medication will also lead to local irritation.

The intravenous injection of methocarbamol can cause a minor release of the amount of hemolysis in the laboratory. An increase in hemoglobin and red blood cells in the urine can be seen.

Leukopenia can occur but is very rare.

In patients with a known or suspected history of epilepsy, parenteral dosage forms should be used with caution.

Although a causal relationship has not yet been established, seizures have been reported during the intravenous administration of Methocarbamol.

Methocarbamol can affect the mental and physical capacities required to perform dangerous activities requiring mental attention or coordination, such as operating machinery or equipment and driving a vehicle.

The patient should not operate machinery, including cars until they are sure that methocarbamol therapy will not adversely affect their ability to participate in these activities.

The injection of methocarbamol should not be administered to patients with renal failure since the polyethylene glycol vehicle can irritate the kidneys.

The safety and efficacy of methocarbamol, other than in treating tetanus, in children under 12 years of age have not been established.

Therefore, this medication should not be administered to children in this age group.

Geriatric patients are much more likely to have impaired renal function.

This condition does not allow the administration of parenteral methocarbamol and the restriction of other relaxants of skeletal muscle, which should be used with caution and under strict medical observation.

Because methocarbamol may have a general depressant effect on the central nervous system, patients receiving methocarbamol treatment should not combine the use of alcohol and other central nervous system depressants.

The safe use of methocarbamol has not yet been established through research; the possible adverse effects caused by treatment on fetal development have not been determined.

However, some fetal and congenital abnormalities have been reported after the administration of methocarbamol.

That is why methocarbamol tablets should not be used in pregnant women or have a chance of becoming pregnant.

This restriction should be mainly observed, during early pregnancy, unless, in the physician’s judgment, the potential benefits of the medication outweigh the possible risks to the fetus.

In the case of lactating mothers, research has been conducted on methocarbamol and its metabolites in animals. It has been reported that they are excreted in the milk of dogs.

However, it is not sure if methocarbamol or its metabolites are excreted in human milk.

However, because many drugs are excreted in human milk, caution should be exercised when methocarbamol is administered to a nursing woman, and treatment or breastfeeding should be discontinued.

Its pediatric use is not recommended in patients under 16 years of age since the safety and efficacy of methocarbamol in pediatric patients have not been established.


Methocarbamol can cause interactions between drug and laboratory tests.

This medication may cause color interference in some 5-hydroxy indole acetic acid tests when the nitrosonaphthol reagent is used—those tests for urinary vanillylmandelic acid in the Gitlow method.

Methocarbamol should be used with great caution in the case of patients suffering from myasthenia gravis.

As well as those who receive treatment with anticholinesterase agents, since this can inhibit the effects of pyridostigmine bromide.