Methocarbamol is a centrally-acting skeletal muscle relaxant used as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. It is a carbamate derivative of guaifenesin. Its precise mechanism is not fully understood but is believed to involve central nervous system depression, leading to muscle relaxation without directly affecting the contractile mechanism of striated muscle, the motor end plate, or the nerve fiber.
Adult: Initial dose: 1.5 grams (three 500mg tablets) four times a day for the first 48-72 hours. For severe conditions, 2 grams (four 500mg tablets) four times a day may be used. Maintenance dose: 1 gram (two 500mg tablets) four times a day, or 1.5 grams (three 500mg tablets) three times a day.
Note: Take with or without food. Tablets should be swallowed whole with a full glass of water. Do not crush or chew. May be taken with food if gastrointestinal upset occurs.
The exact mechanism of action of methocarbamol is not fully elucidated. It does not directly relax tense skeletal muscles. It is believed to exert its effects by general central nervous system (CNS) depression. It may inhibit polysynaptic reflexes in the spinal cord and descending reticular formation, leading to a reduction in skeletal muscle hyperactivity and spasm associated with acute painful conditions.
Pregnancy: Pregnancy Category C (US FDA). Animal studies have shown adverse effects. There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus, especially in the first trimester.
Driving: NOT ADVISABLE. Methocarbamol can cause significant drowsiness, dizziness, and blurred vision, impairing the ability to drive or operate machinery. Patients should not engage in these activities until they know how the drug affects them.
| CNS Depressants (Alcohol, Benzodiazepines, Opioids, Sedative Antihistamines) | Additive CNS depression, increased risk of sedation, dizziness, respiratory depression, and impaired psychomotor performance. | Major |
| Anticholinergic Drugs (e.g., Tricyclic Antidepressants, Atropine) | Increased risk of anticholinergic side effects like dry mouth, urinary retention, constipation. | Moderate |
| Pyridostigmine (and other Cholinesterase Inhibitors) | Methocarbamol may antagonize the effects in myasthenia gravis. | Moderate |
| CYP1A2 Inhibitors (e.g., Ciprofloxacin, Fluvoxamine) | May increase methocarbamol plasma concentrations, increasing risk of adverse effects. | Moderate |
| MAO Inhibitors (e.g., Phenelzine, Selegiline) | Theoretical risk of enhanced CNS depression or hypertensive crisis; use with extreme caution. | Major |
Same composition (Methocarbamol (500mg)), different brands: