phenylefrin

Phenylephrine, sometimes spelled phenylefrin, is a selective α1-adrenergic receptor agonist used as a decongestant, a mydriatic agent in ophthalmology, and a vasopressor to raise blood pressure in acute care settings.

Its primary action is vasoconstriction of arterial smooth muscle mediated by α1 receptors, reducing nasal mucosal swelling and congestion. In the eye, stimulation of the iris radial muscle causes pupil dilation (mydriasis) with little effect on accommodation.

Phenylephrine is administered by intranasal spray, oral tablet, ophthalmic drops, or intravenous/intramuscular injection. Oral bioavailability is low due to first-pass metabolism, and efficacy as a nasal decongestant at standard doses is debated; in many over-the-counter preparations, pseudoephedrine is used instead for greater effect.

Contraindications include uncontrolled hypertension, tachyarrhythmias, ischemic heart disease, and narrow-angle glaucoma. Caution is advised during pregnancy and in patients taking monoamine oxidase inhibitors or certain antidepressants, due to potential hypertensive crises and drug interactions.

Common adverse effects are hypertension, headache, reflex bradycardia, palpitations, and anxiety; nasal sprays may cause local irritation. Pharmacokinetics vary by route; peak plasma levels occur within 30–60 minutes after oral dosing, with a short duration of action and hepatic metabolism.