Orphenadrine Citrate

Pronunciation: ore-FEN-uh-dreen SIH-trate
Class: Skeletal muscle relaxant

Trade Names

Norflex
- Injection 30 mg/mL

Orphenadrine Citrate
- Tablets, sustained-release 100 mg

Pharmacology

Unknown; may be related to analgesic properties since drug acts on brain stem and does not act directly on muscles; possesses anticholinergic actions.

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Pharmacokinetics

Absorption

Readily absorbed from the GI tract. T _max is 2 h.

Distribution

Not fully characterized.

Metabolism

Degraded to 8 known metabolites.

Elimination

Eliminated through urine (as metabolites, small amount as unchanged) and feces. The t _½ is approximately 14 h (parent drug). The t _½ is 2 to 25 h (metabolites).

Duration

4 to 6 h.

Indications and Usage

Adjunctive treatment for acute, painful musculoskeletal conditions.

Unlabeled Uses

Treatment of quinine-resistant leg cramps.

Contraindications

Glaucoma; pyloric or duodenal obstruction; stenosing peptic ulcers; prostatic hypertrophy; obstruction of bladder neck; esophageal achalasia; myasthenia gravis.

Dosage and Administration

IV/IM 60 mg every 12 h as needed.

PO 100 mg twice daily.

Drug Interactions

Increased CNS depression.

Worsening schizophrenic symptoms, decreased haloperidol levels, tardive dyskinesia.

Decreased effects of phenothiazines.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Tachycardia; palpitations; transient syncope.

CNS

Weakness; headache; dizziness; lightheadedness; confusion (especially in elderly); hallucinations; agitation; tremor; drowsiness.

Dermatologic

Hypersensitivity reactions (eg, rashes).

EENT

Blurred vision; pupil dilation; increased ocular tension.

GI

Dry mouth; vomiting; nausea; constipation; gastric irritation.

Genitourinary

Urinary hesitancy and retention.

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Elderly

May be more sensitive to anticholinergic effects.

Hypersensitivity

May occur.

Sulfite Sensitivity

Some products contain bisulfites, which may cause allergic-type reactions in certain persons.

Cardiac disease

Use drug with caution in patients with cardiac decompensation, coronary insufficiency, cardiac arrhythmias or tachycardia.

Heat prostration

Can occur in presence of high environmental temperature.

Overdosage

Symptoms

Cardiac arrhythmias, seizures, coma, shock.

Patient Information

• Tell patient not to increase dosage of medication. Even slight overdose may be highly toxic.
• Instruct patient to take sips of water frequently, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.
• Advise patient that drug may cause drowsiness or dizziness, and to use caution while driving or performing other tasks requiring mental alertness.
• Instruct patient to report the following symptoms to health care provider: urinary retention, constipation, palpitations, or tremors.
• Instruct patient to avoid alcohol or other CNS depressants.

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