Phenylephrine

Generic name: Phenylephrine

Drug class: Sympathomimetic amines

Dosage form: Oral tablets, nasal spray, ophthalmic solution, injectable solution

Root of administration: Oral, nasal, ophthalmic, intravenous

Dose:

• Oral tablets: 10 mg every 4 hours; do not exceed 6 tablets in 24 hours.
• Nasal spray: Follow package instructions; typically 1-2 sprays in each nostril every 4 hours; do not exceed 3 doses in 24 hours.
• Ophthalmic solution: 2.5% or 10% solution; applied as directed by healthcare provider, usually 1 drop in the affected eye(s) every 3-7 days.
• Injectable solution: For adults undergoing surgery with neuraxial or general anesthesia: initial dose of 50 to 250 mcg by intravenous bolus; maintenance dose of 0.5 to 1.4 mcg/kg/min by intravenous continuous infusion, titrated to blood pressure goal.

Mechanism of action: Phenylephrine is a selective α₁-adrenergic receptor agonist that causes vasoconstriction, leading to reduced swelling and congestion in nasal passages and sinuses, and increased blood pressure in cases of hypotension.

Drug usage cases:

• Temporary relief of nasal congestion due to the common cold, hay fever, or other upper respiratory allergies.
• Management of hypotension during anesthesia.
• Induction of mydriasis (pupil dilation) during eye examinations.
• Treatment of hemorrhoids to reduce swelling and discomfort.

Drug contraindications:

• Hypersensitivity to phenylephrine or any component of the formulation.
• Severe hypertension or severe coronary artery disease.
• Concurrent use with monoamine oxidase inhibitors (MAOIs) or within 14 days of stopping an MAOI.
• Narrow-angle glaucoma (for ophthalmic use).
• Use in neonates and infants under 2 years of age (for oral and nasal use).

Side effects:

• Common: Headache, dizziness, nausea, vomiting, restlessness, insomnia, increased blood pressure, reflex bradycardia.
• Serious: Chest pain, arrhythmias, severe hypertension, urinary retention, blurred vision, anxiety, tremors, palpitations, difficulty breathing, skin irritation (with topical use).

Warnings:

• Use with caution in patients with cardiovascular disease, hypertension, hyperthyroidism, diabetes, or prostate enlargement.
• Monitor blood pressure regularly during treatment, especially in patients with pre-existing hypertension.
• Avoid concurrent use with other sympathomimetic drugs to prevent additive effects.
• Topical use may cause local irritation; discontinue if severe irritation occurs.
• Intravenous use may cause tissue necrosis if extravasation occurs; ensure proper intravenous access.
• Use in pregnancy only if clearly needed; phenylephrine is excreted in breast milk; exercise caution when administering to nursing mothers.

Use during pregnancy or breastfeeding: Phenylephrine is classified as a Category C drug for pregnancy, indicating that risk cannot be ruled out. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Phenylephrine is excreted in breast milk; caution is advised when administering to nursing mothers, as the effects on a nursing infant are unknown.