What is the recommended dosing for orphenadrine (muscle relaxant)?

Orphenadrine Dosing Recommendations

The recommended dosing for orphenadrine is 60 mg intravenously or intramuscularly every 12 hours, or 100 mg orally twice daily for maintenance therapy. 1

Adult Dosing

• Parenteral (IV/IM): 60 mg (one 2 mL vial) every 12 hours 1
• Oral: 100 mg twice daily for maintenance therapy 1

Clinical Considerations

Mechanism and Use

• Orphenadrine is a centrally acting skeletal muscle relaxant with anticholinergic properties 2
• The precise mechanism of action is unclear but appears to include anticholinergic effects 2
• Used primarily for relief of discomfort associated with acute painful musculoskeletal conditions 3

Perioperative Management

• Hold on the day of surgical procedures 2
• Discontinuation is recommended due to anticholinergic effects that may cause cardiovascular instability during surgery 2

Precautions and Contraindications

• Use with caution in patients with:
  • Tachycardia or cardiac arrhythmias 2
  • Cardiac decompensation or coronary insufficiency 2
  • Elderly patients (increased sensitivity to anticholinergic effects) 2
• Contraindicated in patients with:
  • Gastrointestinal tract obstruction 2
  • Stenosing peptic ulcer disease 2
  • Prostatic hypertrophy or bladder outlet obstruction 2
  • Glaucoma 2
  • Myasthenia gravis 2

Adverse Effects

• Common anticholinergic side effects include:
  • Confusion and anxiety 2
  • Tremors 2
  • Urinary retention 2
  • Dry mouth and constipation 2
  • Cardiovascular instability 2
• Potential for drug interactions with other medications having anticholinergic properties 2

Toxicity Considerations

• Doses above therapeutic range can lead to antimuscarinic toxicity 4
• Severe toxicity has been reported with overdoses (typically >2-3g) 5
• Clinical features of toxicity include:
  • Drowsiness and confusion 4
  • Sinus tachycardia 4
  • Seizures in severe cases 5
  • Potential for cardiotoxicity at very high doses 6

Clinical Efficacy

• A randomized trial comparing naproxen+orphenadrine versus naproxen alone for acute low back pain found no significant improvement in functional outcomes when adding orphenadrine 3
• The evidence supporting orphenadrine's superiority over other muscle relaxants or placebo is limited 3

Important Monitoring Considerations

• Monitor for anticholinergic side effects, particularly in elderly patients 2
• Assess for potential drug interactions with other medications that have anticholinergic properties 2
• Parenteral formulations should be visually inspected for particulate matter before administration 1