Side Effects of Robaxin (methocarbamol)

Robaxin (methocarbamol) is a skeletal muscle relaxant with sedative effects used to relieve discomfort associated with painful skeletal muscle spasms. Robaxin is also used to relieve tetanus spasms. 

The exact mechanism of how Robaxin works is not known. Robaxin is presumed to work by depressing the central nervous system, leading to relaxation of muscles. 

Common side effects of Robaxin include

• drowsiness,
• dizziness,
• confusion,
• headache,
• flushing,
• nausea, and
• vomiting.

Serious side effects of Robaxin include

• fever,
• chills,
• flu symptoms,
• lowered heart rate,
• lightheadedness,
• seizures (convulsions), and
• yellowing of skin or eyes (jaundice).

Drug interactions of Robaxin include narcotic painkillers, alcohol, sedative or hypnotic medications, and other medications that depress the central nervous system, because the combination can increase sedation, as well as cause loss of consciousness, troubled breathing, lowered heart rate, and in severe cases, death or coma. 

There are no adequate studies of Robaxin to determine safe and effective use in pregnant women. Robaxin should be avoided in pregnant mothers to avoid any risk to a fetus. 

It is unknown if Robaxin enters breast milk. It should be avoided in breastfeeding mothers to prevent any adverse effects to the newborn.

Common side effects of methocarbamol include:

• drowsiness,
• dizziness,
• lightheadedness,
• confusion,
• headache,
• flushing,
• lowered heart rate,
• nausea, and
• vomiting.

The following adverse reactions have been reported coincident with the administration of methocarbamol. Some events may have been due to an overly rapid rate of intravenous injection.

Body as a whole: Anaphylactic reaction, angioneurotic edema, fever, headache

Cardiovascular system: Bradycardia, flushing, hypotension, syncope, thrombophlebitis

In most cases of syncope there was spontaneous recovery. In others, epinephrine, injectable steroids, and/or injectable antihistamines were employed to hasten recovery.

Digestive system: Dyspepsia, jaundice (including cholestatic jaundice), nausea and vomiting

Hemic and lymphatic system: Leukopenia

Immune system: Hypersensitivity reactions

Nervous system: Amnesia, confusion, diplopia, dizziness or light-headedness, drowsiness, insomnia, mild muscular incoordination, nystagmus, sedation, seizures (including grand mal), vertigo

The onset of convulsive seizures during intravenous administration of methocarbamol has been reported in patients with seizure disorders. The psychic trauma of the procedure may have been a contributing factor. Although several observers have reported success in terminating epileptiform seizures with Robaxin Injectable, its administration to patients with epilepsy is not recommended.

Skin and special senses: Blurred vision, conjunctivitis, nasal congestion, metallic taste, pruritus, rash, urticaria

Other: Pain and sloughing at the site of injection

See prescription labeling for interaction with CNS drugs and alcohol.

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

Drug/Laboratory Test Interactions

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