Drug class:
VA class: MS200

Medically reviewed by Drugs.com on Mar 10, 2024. Written by ASHP.

Introduction

Centrally acting skeletal muscle relaxant.^{110 120 121 122 125}

Uses for Orphenadrine

Muscular Conditions

Used alone or in combination with aspirin and caffeine as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.^{120 121 122}

If pharmacologic therapy is required for acute low back pain (usually a benign and self-limiting condition^{105 106 108} ), experts state that an NSAIA or skeletal muscle relaxant may be considered.¹⁰⁹ Skeletal muscle relaxants may provide small improvements in pain relief, but are associated with a high incidence of adverse effects (e.g., CNS effects).^{104 106 107 108 109} Use with caution after weighing risks against benefits.^{104 106 107 108}

Various skeletal muscle relaxants appear to have comparable efficacy for low back pain relief.^{103 104 106 108}

Orphenadrine Dosage and Administration

Administration

Administer orally or by IV or IM injection.^{120 121 122}

Oral Administration

Administer extended-release tablets orally twice daily (once in the morning and once in the evening).¹²⁰

Administer fixed-combination tablets (with aspirin and caffeine) orally 3 or 4 times daily.¹²²

IV Administration

Place patient in supine position during and for 5–10 minutes following IV injection.^a (See CNS Effects under Cautions.) To minimize adverse reactions, assist patient from recumbent position after the drug is administered.^a

Rate of Administration

Administer IV over about 5 minutes.^a

Dosage

Available as orphenadrine citrate; dosage expressed in terms of the salt.^{120 121 122}

Adults

Muscular Conditions

Extended-release Tablets

Oral

100 mg twice daily.¹²⁰

Fixed-combination Tablets

Oral

25–50 mg (in combination with aspirin 385–770 mg and caffeine 30–60 mg) 3 or 4 times daily.¹²²

Parenteral Therapy

IV or IM

60 mg every 12 hours.¹²¹

Cautions for Orphenadrine

Contraindications

• Glaucoma.^{120 121}

• Pyloric or duodenal obstruction.^{120 121}

• Stenosing peptic ulcers.^{120 121}

• Prostatic hypertrophy or obstruction of the bladder neck.^{120 121}

• Cardiospasm (megaesophagus).^{120 121}

• Myasthenia gravis.^{120 121}

• Known hypersensitivity to orphenadrine or any ingredient in the formulation.^{120 121}

Warnings/Precautions

Warnings

CNS Effects

Transient episodes of lightheadedness, dizziness, or syncope reported.^{120 121}

Performance of activities requiring mental alertness or physical coordination (e.g., operating machinery, driving a motor vehicle) may be impaired.^{120 121}

Sensitivity Reactions

Sulfite Sensitivity

Injectable formulation contains sodium bisulfite, which can cause allergic-type reactions, including anaphylaxis and life-threatening or less severe asthmatic episodes, in certain susceptible individuals.^{100 121}

Overall prevalence of sulfite sensitivity in the general population unknown but probably low; such sensitivity appears to occur more frequently in asthmatic than in nonasthmatic individuals.^{100 121}

General Precautions

Adequate Patient Monitoring

Safety of continuous therapy not established.^{120 121} Perform periodic blood, urine, and liver function tests during prolonged orphenadrine therapy^{120 121}

Cardiac Effects

Possible tachycardia and palpitation; may be associated with increased dosages.^{120 121} Use with caution in patients with tachycardia, cardiac decompensation, coronary insufficiency, or cardiac arrhythmias.^{120 121}

Use of Fixed Combinations

When orphenadrine is used in fixed combination with aspirin and caffeine, consider the cautions, precautions, and contraindications associated with each agent in the combination.¹²²

Specific Populations

Pregnancy

Category C.¹²⁰

Not known whether the drug can cause fetal harm or affect reproductive capacity.^{120 121} Use during pregnancy only if potential benefits outweigh potential risks, particularly during early pregnancy.^{120 121}

Lactation

Not known whether orphenadrine is distributed into milk; use with caution.^a

Pediatric Use

Safety and efficacy not established.^{120 121}

Geriatric Use

Because of risk of injury, skeletal muscle relaxants should generally be avoided in geriatric patients.¹¹¹

Common Adverse Effects

Dry mouth, tachycardia, palpitation, urinary hesitancy or retention, blurred vision, dilatation of pupils, increased intraocular pressure, weakness, nausea, vomiting, headache, dizziness, constipation, drowsiness.^{120 121}

Orphenadrine Pharmacokinetics

Absorption

Bioavailability

Readily absorbed following oral administration.^a

Distribution

Extent

Distribution not fully characterized in humans.^a In animals, detected in all organs, especially those with greatest perfusion (e.g., lungs).^a

Orphenadrine may cross the placenta; not known whether distributed into milk.^a

Elimination

Metabolism

Almost completely metabolized to at least 8 metabolites; however, metabolic fate not fully determined.^a

Elimination Route

Eliminated principally in urine as metabolites and, in small amounts, as unchanged drug.^a

Half-life

Approximately 14 hours.^a

Stability

Storage

Oral

Tablets

20–25°C in tight, light-resistant containers.¹²⁰

Parenteral

Injection

20–25°C.¹²¹ Protect from light; do not use if precipitation occurs.¹²¹

Actions

• Centrally acting skeletal muscle relaxant.^{110 120 121 122 125}

• Precise mechanism of action not known.^{120 121} Does not directly relax skeletal muscle;^{120 121} therapeutic action may be related to analgesic properties.^{120 121}

• May reduce skeletal muscle spasm, possibly through an atropine-like central action on cerebral motor centers or on the medulla.^a

• Exhibits postganglionic anticholinergic, antihistaminic, and local anesthetic properties.^a

Advice to Patients

• Potential to impair mental alertness or physical coordination; use caution when driving or operating machinery until effects on individual are known.^{120 121}

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as concomitant illnesses.^{120 121}

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.^{120 121}

• Importance of informing patients of other important precautionary information.^{120 121} (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

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