Skeletal Muscle Relaxant
Action And Clinical Pharmacology: The mechanism of action of methocarbamol has not been established, but may be due to general CNS depression. It has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber. Methocarbamol is metabolized to yield a dealkylated and a hydroxylated product. These 2 metabolites are found primarily as glucuronide and sulfate conjugates. Based on elimination of radioactivity, the half-life of methocarbamol and its metabolites is about 2 hours. Animal studies reveal that methocarbamol crosses the placental barrier and blood-brain barrier.
Indications And Clinical Uses: An adjunct to rest, physical therapy and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions.
Contra-Indications: Hypersensitivity to methocarbamol.
Precautions: Occupational Hazards: Methocarbamol may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle; ambulatory patients should therefore be cautioned accordingly. Patients should be cautioned about combined effects of methocarbamol with alcohol and with other CNS depressants.
Methocarbamol may cause a color interference in screening tests for 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).
Pregnancy: Safe use in pregnancy has not been established with regard to possible adverse effects in fetal development.
Lactation: It is not known whether methocarbamol is excreted in human milk.
Children: Safety and effectiveness in children 12 years of age and less have not been established.
Adverse Reactions: Following oral administration, minor untoward effects such as lightheadedness, dizziness, drowsiness and mild nausea occasionally occur, and frequently disappear on reduction of dosage (seen in approximately 4 to 5% of patients). Allergic manifestations such as urticaria, pruritus, rash or conjunctivitis with nasal congestion have been reported in a few hypersensitive patients.
Symptoms And Treatment Of Overdose: Symptoms: No deaths or major toxicity have been reported from overdosage with methocarbamol, administered parenterally or orally. One adult survived the deliberate ingestion of 22 to 30 g of methocarbamol without serious toxicity. Another survived 30 to 50 g. The principal symptom was drowsiness in both cases.
Treatment: Reduction of dosage. Supportive therapy for 24 hours as methocarbamol is excreted within that period of time.
Dosage: Adults: 6 g daily for first 48 to 72 hours of acute skeletal muscle spasm. Severe conditions: 8 g daily. Thereafter reduce dosage to 4 g daily.
Availability And Storage: Robaxin: Each white, scored, compressed tablet, engraved “WR”, contains: methocarbamol 500 mg. Nonmedicinal ingredients: cornstarch, magnesium stearate, povidone, sodium lauryl sulfate, sodium starch glycolate and stearic acid. Energy:
Robaxin-750: Each white, scored, capsule-shaped tablet, monogrammed “WR”, contains: methocarbamol 750 mg. Nonmedicinal ingredients: cornstarch, magnesium stearate, povidone, sodium lauryl sulfate, sodium starch glycolate and stearic acid. Energy:
ROBAXIN® ROBAXIN®-750 Whitehall-Robins Methocarbamol Skeletal Muscle Relaxant
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