Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content ++ Pharmacology. Methocarbamol is a centrally acting muscle relaxant. It does not directly relax skeletal muscle and does not depress neuromuscular transmission or muscle excitability; muscle relaxation is probably related to its sedative effects. After intravenous administration, the onset of action is nearly immediate. Elimination occurs by hepatic metabolism, with a serum half-life of 0.9–2.2 hours.IndicationsControl of painful muscle spasm caused by black widow spider envenomation (See Spiders). Methocarbamol should be used as an adjunct to other medications (eg, morphine, diazepam) that are considered more effective.Management of muscle spasm caused by mild tetanus (See Tetanus) or strychnine (See Strychnine) poisoning.ContraindicationsKnown hypersensitivity to the drug.History of epilepsy (intravenous methocarbamol may precipitate seizures).Adverse effectsDizziness, drowsiness, nausea, flushing, and metallic taste may occur.Extravasation from an intravenous site may cause phlebitis and sloughing. Do not administer subcutaneously.Hypotension, bradycardia, and syncope have occurred after intramuscular or intravenous administration. Keep the patient in a recumbent position for 10–15 minutes after injection.Urticaria and anaphylactic reactions have been reported.Use in pregnancy. There is no reported experience, and no FDA category has been assigned.Drug or laboratory interactionsMethocarbamol produces additive sedation with alcohol and other CNS depressants.Methocarbamol may cause false-positive urine test results for 5-hydroxyindole acetic acid (5-HIAA) and vanillylmandelic acid (VMA).The urine may turn brown, black, or blue after it stands.Dosage and method of administrationParenteralAdminister 1 g (children: 15 mg/kg) IV over 5 minutes, followed by 0.5 g in 250 mL of 5% dextrose (children: 10 mg/kg in 5 mL of 5% dextrose) over 4 hours. Repeat every 6 hours to a maximum of 3 g daily.For tetanus, higher doses are usually recommended. Give 1–2 g IV initially, no faster than 300 mg/min; if needed, use a continuous infusion up to a total of 3 g.The usual intramuscular dose is 500 mg every 8 hours for adults and 10 mg/kg every 8 hours for children. Do not inject more than 5 mL into the gluteal region. Do not give subcutaneously.Oral. Switch to oral administration as soon as tolerated. Give 0.5–1 g (children: 10–15 mg/kg) PO or by gastric tube every 6 hours. The maximum dose is 1.5 g every 6 hours; for tetanus, the maximum adult dose is 24 g/d.FormulationsParenteral. Methocarbamol (Robaxin, others), 100 mg/mL in 10-mL vials (in solution with polyethylene glycol).Oral. Methocarbamol (Robaxin, others), 500- and 750-mg tablets.Suggested minimum stocking levels to treat a 100-kg adult for the first 8 hours and 24 hours: methocarbamol, first 8 hours: 8 g or eight vials (100 mg/mL, 10 mL each); first 24 hours: 24 g or 24 vials (100 mg/mL, 10 mL each). Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth