Limited information is available on the acute toxicity of methocarbamol. Overdose of methocarbamol is frequently in conjunction with alcohol or other CNS depressants and includes the following symptoms: nausea, drowsiness, blurred vision, hypotension, seizures and coma. One adult survived the deliberate ingestion of 22 to 30 grams of methocarbamol without serious toxicity. Another adult survived a dose of 30 to 50 grams. The principal symptom in both cases was extreme drowsiness. Treatment was symptomatic and recovery was uneventful. However, there have been cases of fatal overdose.
Management of overdose includes symptomatic and supportive treatment. Supportive measures include maintenance of an adequate airway, monitoring urinary output and vital signs, and administration of intravenous fluids if necessary. The usefulness of haemodialysis in managing overdose is unknown.
Coma or pre-coma states. Known brain damage or epilepsy. Myasthenia gravis.
Not applicable.
Adverse reactions reported coincident with the administration of methocarbamol include
Body as a whole: Angioneurotic oedema, anaphylactic reaction, fever, headache.
Cardiovascular system: Bradycardia, flushing, hypotension, syncope.
Digestive system: Dyspepsia, jaundice (including cholestatic jaundice), nausea and vomiting.
Blood and lymphatic system: Leucopenia.
Nervous system: Restlessness, anxiety, tremor, amnesia, confusion, diplopia, dizziness or light-headedness, vertigo, drowsiness, insomnia, mild muscular incoordination, nystagmus, seizures (including grand mal).
Skin and special senses: Blurred vision, conjunctivitis with nasal congestion, metallic taste, pruritus, rash, urticaria.
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme, Website: www.mhra.gov.uk/yellowcard.
Nothing of note to the prescriber.
As a short-term adjunct to the symptomatic treatment of acute musculoskeletal disorders associated with painful muscle spasms.
Pharmacotherapeutic group: Muscle relaxants, centrally acting agents; Carbamic acid esters, ATC code: M03BA03.
Myomethol-750 is used as a short-term adjunct to the symptomatic treatment of acute musculoskeletal disorders associated with painful muscle spasms.
The mechanism of action of methocarbamol in humans has not been established, but may be due to general central nervous system depression. It has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fibre.
Methocarbamol is absorbed from the gastro-intestinal tract and produces peak plasma concentrations after about 1-3 hours. Its activity derives from the intact molecule and only a small proportion is converted to guaiphenesin.
Renally impaired
The clearance of methocarbamol in renally-impaired patients on maintenance haemodialysis was reduced about 40% compared to a normal population, although the mean elimination half-life in these two groups was similar (1.2 versus 1.1 hours, respectively).
Hepatically impaired
In patients with cirrhosis secondary to alcohol abuse, the mean total clearance of methocarbamol was reduced approximately 70% compared to a normal population (11.9 L/hr), and the mean elimination half-life was extended to approximately 3.4 hours. The fraction of methocarbamol bound to plasma proteins was decreased to approximately 40 to 45% compared to 46 to 50% in an age- and weight-matched normal population.
Myomethol-750 should be used with caution in patients with renal and hepatic insufficiency.
This product may cause drowsiness and patients receiving it should not drive nor operate machinery unless their physical and mental capabilities remain unaffected - especially if other medication capable of causing drowsiness is also being taken.
For oral use.
Posology
Adults: The usual dose is 2 tablets four times daily but therapeutic response has been achieved with doses as low as 1 tablet three times daily.
Elderly: Half the maximum dose or less may be sufficient to produce a therapeutic response.
Paediatric population
Not recommended.
Hepatically impaired
In patients with chronic hepatic disease the elimination half-life may be prolonged. Therefore, consideration should be given to increasing the dose interval.
None
