Robaxin (Methocarbamol)

(British Approved Name, US Adopted Name, rINN)

Drug Nomenclature

International Nonproprietary Names (INNs) in main languages (French, Latin, Russian, and Spanish):

Synonyms: Guaiphenesin Carbamate; Methocarbamolum; Metocarbamol; Metokarbamol; Metokarbamoli

Pharmacopoeias. In US.

The United States Pharmacopeia 31, 2008, and Supplements 1 and 2 (Methocarbamol). A white powder, odourless or having a slight characteristic odour. M.p. about 94° or, if previously ground to a fine powder, about 90°. Soluble 1 in 40 of water at 20°; sparingly soluble in chloroform; soluble in alcohol only with heating; insoluble in n-hexane and in benzene. Store in airtight containers.

Adverse Effects

Adverse effects reported with methocarbamol include nausea, vomiting, anorexia, lightheadedness, dizziness, lassitude, drowsiness, restlessness, anxiety, confusion, tremor, vertigo, blurred vision, fever, headache, convulsions, and hypersensitivity reactions including rashes, pruritus, urticaria, angioedema, and conjunctivitis with nasal congestion.

After injection patients may experience flushing and a metallic taste; incoordination, diplopia, nystagmus, vertigo, syncope, hypotension, bradycardia, and anaphylaxis have been reported. There may be sloughing and thrombophlebitis at the site of injection.

Precautions

Methocarbamol is contra-indicated in coma or pre-coma states, brain damage, myasthenia gravis, or in patients with a history of epilepsy. Caution is advisable in renal or hepatic impairment.

Methocarbamol may cause drowsiness; patients affected should not drive or operate machinery.

Preparations for injection may contain, as a solvent, a macrogol which could increase existing acidosis and urea retention in patients with renal impairment; such preparations should not be used in patients with known or suspected renal disease.

Abnormal coloration

Methocarbamol has been reported to cause brown to black or green discoloration of the urine on standing.

Interactions

The CNS effects of methocarbamol may be potentiated by alcohol or other CNS depressants. Methocarbamol has also been reported to potentiate the effects of anorectics and antimuscarinics, and to inhibit the effect of pyridostigmine.

Pharmacokinetics

Methocarbamol is rapidly and almost completely absorbed from the gastrointestinal tract after oral doses. Its plasma half-life is reported to be about 1 to 2 hours. It is metabolised by dealkylation and hydroxylation and is excreted in urine primarily as the glucuronide and sulfate conjugates of its metabolites. A small amount is excreted in faeces.

Uses and Administration

Methocarbamol is a centrally acting skeletal muscle relaxant whose action may be due to general depressant effects on the CNS.

Methocarbamol is used as an adjunct in the short-term symptomatic treatment of painful muscle spasm associated with musculoskeletal conditions. It is sometimes given with analgesics in compound preparations for the treatment of musculoskeletal pain.

The usual initial oral dose for muscle spasm is 1.5 g four times daily, reduced to a maintenance dose of about 4 g daily after 2 to 3 days. A dose of 750 mg three times daily may be sufficient for a therapeutic effect. Half the maximum daily dose or less may be sufficient for elderly patients.

Methocarbamol has also been given intravenously at a rate of not more than 300 mg/minute, by slow injection or by infusion in sodium chloride 0.9% or glucose 5% injection. The parenteral route should not be used for more than 3 consecutive days and the dose should not exceed 3 g daily. The patient should remain lying down during, and for 10 to 15 minutes after, intravenous doses. The US manufacturers state that the injection is hyperton-ic and extravasation should be avoided. However, it may also be given by intramuscular injection in a dose of up to 500 mg into each gluteal region at intervals of 8 hours.

Preparations

The United States Pharmacopeia 31, 2008, and Supplements 1 and 2: Methocarbamol Injection; Methocarbamol Tablets.

Proprietary Preparations

Canada: Robaxin;

France: Lumirelax;

Germany; Ortoton;

Hong Kong; Robaxin ;

India: Robinax;

Mexico: Remisol; Rexivin;

South Africa: Robaxin;

Spain: Robaxin;

Thailand: Laxan; Manobaxine; Musxan; Myocin ; Myomethol; Robaxin ;

United Kingdom (UK): Robaxin;

United States of America (US and USA): Robaxin.

Multi-ingredient

Canada: Aspirin Backache; Dodds Back Ease; Methox-acet; Methoxacet-C; Methoxisal; Methoxisal-C; Muscle & Back Pain Relie ; Muscle & Back Pain Relief Extra Strength; Muscle & Back Pain Relief-8; Muscle Relaxant and Analgesic ; Obusforme ; Relaxophen; Robax Platinum; Robaxacet; Robaxacet-8; Robaxisal; Robaxisal-C; Spasmhalt; Spasmhalt-ASA;

Germany; Ortoton Plus;

India: Flexinol; Ibugesic-M; Robiflam; Robinaxol;

Mexico: Artridol; Carbafen; Carbager-Plus; Carbamox; Dolocam Plus; Flexamol; Malival Compuesto; Morlan; Remisol-Plus; Retoflam F; Reupat; Robaxifen; Robaxisal; Vengesic ;

South Africa: Robaxisal;

Spain: Robaxisal Compuesto; Robaxisal ;

Turkey: Miyorel;

Venezuela: Beseroldos; Robaxifen; Robaxisal.

Muscle relaxants

Zanaflex

Jennifer Bowles

Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.