Phenylephrine information from DrugsUpdate
P - Caution when used during pregnancy
Phenylephrine or Neo-Synephrine is an α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure. Phenylephrine has recently been marketed as a substitute for pseudoephedrine (e.g.,Sudafed (Original Formulation)), but there are recent claims that oral phenylephrine may be no more effective as a decongestant than a placebo.
Pharmacodynamics
Stimulates postsynaptic alpha receptors, resulting in rise in intense arterial peripheral vasoconstriction. Causes marked increase in systolic, diastolic, and pulmonary pressures, as well as reflex bradycardia. Slightly decreases cardiac output and increases coronary blood flow.
Pharmacokinetics
Metabolism
In liver and GI.
Onset
Rapid (IV).
Duration
20 min (IV); 50 min (subcutaneous).
Phenylephrine Indications / Phenylephrine Uses
Information Not Available
Phenylephrine Adverse Reactions / Phenylephrine Side Effects
Cardiovascular
Angina; arrhythmias; bradycardia; CV collapse with hypotension; fatal subarachnoid hemorrhage; hypertension; MI; syncope; tachycardia.
CNS
Anxiety; CNS depression; convulsions; dizziness; excitability; fear; hallucinations; headache; insomnia; nervousness; pallor; restlessness; tremor; weakness.
EENT
With ophthalmic and intranasal forms: blurring of vision; rebound congestion; transitory stinging on initial instillation.
GI
Nausea.
Genitourinary
Dysuria; urinary retention.
Respiratory
Respiratory difficulty.
Precautions
Warnings
Injection
Health care providers should completely familiarize themselves with the complete contents of the product information before prescribing phenylephrine injection.
Monitor
Check BP frequently during continuous infusion; monitor BP in elderly patients with known cardiac disease.
Special Precautions
Information Not Available
Other Drug Interactions
Atropine
Concurrent use may enhance the pressor effects and induce tachycardia, especially in infants.
Beta-blockers
Decrease phenylephrine's effect.
Digitalis glycosides, general anesthetics
Arrhythmias.
Furazolidone, MAOIs
May significantly increase pressor response resulting in hypertensive crisis and intracranial hemorrhage.
Guanethidine, methyldopa, reserpine
May increase pressor response of phenylephrine; resulting in severe hypertension.
Halogenated hydrocarbon anesthetics
May sensitize myocardium to effects of catecholamines. Use extreme caution to avoid arrhythmias.
Oxytocic drugs
May cause severe persistent hypertension.
Tricyclic antidepressants
May decrease or increase response; use with caution.
Laboratory Test Interactions
Products with potassium guaiacolsulfonate may increase renal Cl for urate and thereby lower serum uric acid levels; may increase urinary 50 hydroxyindoleacetic acid; may falsely elevate VMA test for catecholis.
Dosage
Mild or Moderate Hypotension
Adults
Subcutaneous / IM 1 to 10 mg (usually 2 to 5 mg); do not exceed initial dose of 5 mg. Avoid repeat injections more often than every 10 to 15 min. IV 0.1 to 0.5 mg (usually 0.2 mg); do not exceed initial dose of 0.5 mg. Avoid repeat injections more often than every 10 to 15 min.
Severe Hypotension and Shock
Adults
IV continuous infusion For initial dose, give 100 to 180 mcg/min of 1:50,000 solution (10 mg per 500 mL of dextrose injection or sodium chloride); once BP has stabilized to low normal level, decrease to maintenance rate of 40 to 60 mcg/min. If prompt initial vasopressor response is not obtained, increase dosage in increments greater than or equal to 10 mg and add to infusion; adjust rate until desired BP is obtained.
Hypotension of Spinal Anesthesia
Adults
Subcutaneous / IM 2 to 3 mg three to four min before injection of anesthetic. IV For hypotensive emergencies during spinal anesthesia, inject 0.2 mg, increasing by no more than 0.1 to 0.2 mg/dose (max, 0.5 mg/dose).
Children
Subcutaneous / IM 0.5 to 1 mg per 25 lb (55 kg).
Prolongation of Spinal Anesthesia
Adults
2 to 5 mg added to anesthetic solution increases duration of motor block by up to 50%.
Vasoconstriction for Regional Analgesia
Adults
At least 2 mg added to local anesthetic solution in concentration of 1:20,000 (1 mg of phenylephrine per 20 mL of anesthetic solution).
Paroxysmal Supraventricular Tachycardia
Adults
IV
Initial dose
0.5 mg or less via rapid IV push (within 20 to 30 sec); subsequent doses should not exceed preceding dose by more than 0.1 to 0.2 mg (max, 1 mg/dose).
Nasal Congestion
Adults and Children 12 yr of age and older
Intranasal 1 to 2 sprays or 3 drops of 0.25%, 0.5%, or 1% solution every 4 h. Oral 10 to 15 mg every 4 to 6 h, up to 60 mg/day.
Children 6 to 12 yr of age
Intranasal 2 to 3 sprays of 0.25% solution in each nostril every 3 to 4 h. Oral 7.5 mg every 4 to 6 h, up to 30 mg/day.
Children 2 to 6 yr of age
Oral 3.75 mg every 4 to 6 h, up to 15 mg/day.
Children 6 mo to 6 yr of age
Intranasal 1 to 2 drops of 0.16% solution in each nostril every 3 h.
Vasoconstriction/Pupil Dilation
Adults
Ophthalmic Instill 1 drop of 2.5% or 10% on upper limbus. If necessary, repeat after 1 h.
Uveitis/Prevention of Synechiae
Adults
Ophthalmic Instill 2.5% or 10% phenylephrine to the upper surface of the cornea and repeat as necessary, not to exceed 3 times. May continue treatment the following day if necessary. Use with atropine and hot compresses.
Wide-Angle Glaucoma
Adults
Ophthalmic Instill 1 drop of 10% on upper surface of cornea as needed.
Open-Angle Glaucoma
Adults
Ophthalmic Instill 1 drop of 2.5% solution in conjunction with miotics.
Intraocular Surgery
Adults
Ophthalmic Instill 1 drop of 2.5% or 10% solution 30 to 60 min before operation.
Refraction
Adults
Ophthalmic Instill 1 drop of 2.5% solution in conjunction with cycloplegics.
Children
Ophthalmic Instill 1 drop of 2.5% solution in conjunction with cycloplegics.
Ophthalmoscopic Examination
Adults
Ophthalmic Instill 1 drop of 2.5% solution in each eye. Dilation lasts from 1 to 3 h.
Diagnostic Procedures/Provocative Test for Angle-Block in Glaucoma
Adults
Ophthalmic Instill 2.5% solution.
Retinoscopy
Adults
Ophthalmic Instill 2.5% solution.
Blanching Test
Adults
Ophthalmic Instill 1 to 2 drops of 2.5% solution to the injected eye. After 5 min, examine for perilimbal blanching. If blanching occurs, congestion is superficial and probably does not indicate iridocyclitis.
Minor Eye Irritations
Adults
Ophthalmic Instill 1 to 2 drops of 0.12% solution up to 4 times daily.
Food(before/after)
Information Not Available
List of Contraindications
Phenylephrine and Pregnancy
Category C
Phenylephrine and Lactation
Undetermined
Phenylephrine and Children
Consult a doctor before using the tablets in children younger than 12 yr of age; consult a doctor before using the oral liquid in children younger than 2 yr of age. Safety and efficacy of 2.5% ophthalmic solution not established. Ophthalmic use of phenylephrine 10% is contraindicated in infants. Use caution in infants with known cardiac anomalies.
Phenylephrine and Geriatic
Rebound miosis may occur; reinstallation of the drug may produce less mydriasis than previously. Older individuals may also develop transient pigment floaters in the aqueous humor 40 to 45 min after installation.
Phenylephrine and Other Contraindications
Hypersensitivity to any component of the products, potassium guaiacolsulfonate, or to sympathomimetic amines; severe hypertension; ventricular tachycardia; pheochromocytoma; ophthalmic 10% solution contraindicated in infants and patients with aneurysms; low birth weight infants; anatomically narrow angles or narrow-angle glaucoma; during intraocular procedures when the corneal epithelial barrier has been disrupted; elderly patients with severe arteriosclerotic CV or cerebrovascular disease; MAOI use or 14 days after stopping an MAOI; severe coronary artery disease.
Storage
Store at 68° to 77°F and protect from light and excessive heat.
Lab interference
Store at 68° to 77°F and protect from light and excessive heat.
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