Orphenadrine Starting Dose for Mild Stiffness
For mild stiffness, start orphenadrine at 100 mg orally twice daily. 1
FDA-Approved Dosing
The FDA label for orphenadrine specifies that after initial parenteral administration (60 mg IV/IM every 12 hours), relief may be maintained with one 100 mg tablet twice daily for oral therapy. 1 This represents the standard oral maintenance dose and serves as the appropriate starting point for mild stiffness when initiating oral treatment directly.
Key Clinical Considerations
Anticholinergic effects are prominent with orphenadrine, as it is an analog of diphenhydramine with both central and peripheral anticholinergic properties. 2 Common side effects include drowsiness, confusion, sinus tachycardia, and antimuscarinic symptoms. 3
Twice-daily dosing (every 12 hours) is the standard regimen, providing consistent muscle relaxant effects throughout the day. 1
Toxicity can occur at relatively low doses, particularly in vulnerable populations. Children have experienced profound central anticholinergic toxicity (hallucinations, severe agitation, seizures) with as little as 200 mg (two 100 mg tablets). 2, 4 While the question pertains to adults, this underscores the need for caution even at standard dosing.
Important Safety Warnings
Monitor for anticholinergic toxicity: Watch for confusion, agitation, tachycardia, urinary retention, dry mouth, and blurred vision. 2, 3
Avoid in elderly patients or those with cognitive impairment, as anticholinergic medications increase fall risk and delirium. 5
Drug interactions are significant: Orphenadrine can lower plasma concentrations of other medications metabolized hepatically and may have additive anticholinergic effects with other agents. 6
Cardiotoxicity is possible in overdose, though severe cardiac dysrhythmias were not observed in recent case series at doses up to 10 grams. 3 However, ventricular tachycardia has been reported in pediatric poisoning cases. 4
Common Pitfall to Avoid
Do not start with higher doses thinking more aggressive treatment is needed for muscle stiffness—the standard 100 mg twice daily dose is effective for maintenance therapy and minimizes anticholinergic side effects. 1 Escalating beyond this dose increases toxicity risk without clear additional benefit for mild symptoms.