Phenylephrin

Phenylephrin, commonly spelled phenylephrine, is a selective alpha-1 adrenergic receptor agonist used in medicine as a decongestant, vasopressor, and mydriatic agent. It constricts vascular smooth muscle, particularly in mucous membranes, the skin, and the eye, producing vasoconstriction that reduces edema and dilation of the pupil in ophthalmic use.

Medical uses include relief of nasal congestion from colds or allergies when formulated as an intranasal spray or drops; as a vasopressor to raise blood pressure during anesthesia or in certain hypotensive conditions; and as an ophthalmic agent to dilate the pupil for examinations or surgery. It is also employed as a vasoconstrictor added to local anesthetics to prolong anesthesia and reduce bleeding.

Phenylephrin belongs to the catecholamine family and has high alpha-1 selectivity with minimal direct beta-adrenergic activity. Orally administered phenylephrine has limited systemic bioavailability due to extensive first-pass metabolism, so intranasal and injectable forms are common. The onset of nasal decongestion typically occurs within 15–60 minutes, with a duration of about 4–6 hours. The plasma half-life is generally 2–3 hours, and metabolites are mainly excreted in urine.

Safety considerations include potential hypertension, tachycardia, palpitations, headache, and nervousness. Local nasal use can cause irritation or rebound congestion. Caution is advised in patients with cardiovascular disease, hypertension, arrhythmias, glaucoma, or those taking monoamine oxidase inhibitors.

Phenylephrine-containing products are widely used as over-the-counter decongestants, though the efficacy of the oral form is debated due to limited bioavailability; intranasal formulations are often preferred for nasal symptoms. In ophthalmology, concentrations of 2.5%–10% are used for dilation.