methocarbamol (Robaxin)

Introduction

Methocarbamol. Tradename: Robaxin.

Indications

• muscle relaxant*
• treatment of muscle spasms associated with acute, painful musculoskeletal conditions
  • tetanus

* on list of medications to avoid; no proven efficacy

Dosage

• 1000-1500 mg PO QID
• maintenance 500-1000 mg QID
• 1 g IM/IV* every 8 hours (infusion rate < 3 mL/min)

Tabs: 500 & 750 mg.

Injection: 100 mg/mL (10 mL)

* NOT recommend for SC injection

Pharmacokinetics

• excreted as a metabolite mainly in the urine with a small amount in the feces
• 1/2life 1-2 hours

elimination via liver

elimination via kidney

1/2life = 2-2 hours

Adverse effects

• common (> 10%)
  • drowsiness, dizziness, lightheadedness
• less common (1-10%)
  • nausea/vomiting, facial flushing, nystagmus, allergic dermatitis, bradycardia, nasal congestion
• uncommon (< 1%)
  • pain at site of injection, leukopenia, convulsions, fainting, thrombophlebitis, blurred vision, renal impairment
• other
  • urticaria
  • headache
  • may color urine brown, black or green

Mechanism of action

• mechanism not fully established
• may cause general CNS depression
• no direct action on contractile mechanism of striated muscle, motor endplates or nerve endplates
• does NOT directly relax tense skeletal muscles

More general terms

• skeletal muscle relaxant (tranquilizer)

Component of

• aspirin/methocarbamol (Robaxisal)

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=4107