Orphenadrine
NORFLEX
Pronunciation: or-FEN-a-dreen
“No reflex Orphan drain”
muscles → muscle relaxant
What it isAntimuscarinic, H1, and NMDA antagonist used for acute musculoskeletal spasm.
Why this oneUnlike purely sedating relaxants, it adds an NMDA-linked analgesic component, though efficacy evidence is weak.
What limits itAnticholinergic burden makes it poor for older adults. Overdose can be lethal through arrhythmia, seizure, and coma.
Pearls
- Also sold with aspirin and caffeine for acute musculoskeletal pain.
- No advantage shown over cheaper nonopioid analgesics.
Orphenadrine prescription history
Animated chart of estimated U.S. prescriptions per year, Muscle relaxants (1950–2026). Orphenadrine enters in 1959 (estimated).
FDA-approved for
- muscle spasm (~1959)
Principal riskAnticholinergic burden; lethal in overdose
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Adjunct for acute painful musculoskeletal conditions | Adults | 1 tablet BID (one AM, one PM) | 1 tablet BID | 1 tablet BID |
Renal Undefined
Hepatic Undefined
Instructions
- Take one tablet in the morning and one in the evening
Available strengths
- ER tab 100 mg
- inj 30 mg/mL
Contraindications
- Glaucoma
- Pyloric or duodenal obstruction
- Stenosing peptic ulcers
- Prostatic hypertrophy or bladder-neck obstruction
- Cardiospasm (megaesophagus)
- Myasthenia gravis
Cautions
- Anticholinergic effects (dry mouth, tachycardia, urinary retention, blurred vision), dose-related
- Rare aplastic anemia reported
- Mental confusion may occur in elderly patients
Adverse reactions
- Dry mouth
- Tachycardia/palpitation
- Urinary hesitancy or retention
- Blurred vision/mydriasis
- Nausea/vomiting
- Headache
- Dizziness
- Constipation
- Drowsiness
- Agitation/tremor/hallucinations
- Pruritus
Pregnancy Pregnancy Category C; use only if clearly needed
Lactation Undefined
Cost
| Strength | #/mo | generic $ | CostPlus | |
|---|---|---|---|---|
| 100 mg | ER tab | 60 BID | $27.22/mo | offered |
| 30 mg/mL | inj | per unit | $5.73/mL | not offered |
Generic entry1982
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Memory aids: interaction avatars
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Self-check
- Orphenadrine: Which activity adds an analgesic component?
NMDA antagonism. - Orphenadrine: What makes it a poor choice for older adults?
Anticholinergic burden.