Methocarbamol

Methocarbamol is a drug used for short-term musculoskeletal pain. Methocarbamol is often used in combination with physical therapy and pain medications. It is less appropriate for lower back pain. It is also used to a limited extent in rheumatoid arthritis and cerebral palsy. It generally takes effect within half an hour. It is administered by mouth or by injection into a vein.

Methocarbamol was developed in the early 1950s to treat muscle spasticity and associated pain.

Pharmacodynamics

Methacarbamol is a skeletal muscle relaxant with an unknown mechanism of action. However, the mechanism of action of methacarbamol is thought to depend on its depressant effect on the central nervous system. Methacarbamol has been shown to act via blockade of spinal polysynaptic reflexes and decreases nerve transmission in spinal and supraspinal polysynaptic pathways. It also prolongs the refractory period of muscle cells. The substance has no effects on contraction of muscle fibers, motor endplates, or nerve fibers.

Pharmacokinetics

Time to maximum concentration is approximately 1 hour in both healthy patients and hemodialysis patients. Methocarbamol is 46-50% protein-bound in healthy patients. Methocarbamol is metabolized in the liver by demethylation and conjugated by glucuronidation or sulfation and excreted in the urine. The elimination half-life is approximately 1.14 hours.

Side effects

Methocarbamol is a centrally acting skeletal muscle relaxant that has significant adverse effects, particularly on the central nervous system.

Possible side effects include:

• Drowsiness
• blurred vision
• Headache
• Nausea
• Skin rash

Other less common side effects include:

• Ataxia
• stomach upset
• mood changes
• difficulty urinating
• itching
• Fever

Contraindications

In combination with benzodiazepines, barbiturates, codeine, or other muscle relaxants, methocarbamol may cause it to cause potentially life-threatening respiratory depression.

Methocarbamol should not be taken during pregnancy. It is also not recommended to be taken during breastfeeding.