phenylephrine hydrochloride: clinical use

Prescribing considerations

• Confirm the intended route and product: indications, contraindications and pregnancy advice differ substantially.
• Assess cardiovascular disease, blood pressure, thyroid disease, diabetes, peripheral vascular disease, glaucoma and interacting medicines.
• For eye use, assess the anterior chamber angle where narrow-angle glaucoma is a concern and minimise systemic absorption with nasolacrimal occlusion.
• Injection should be given by trained clinicians; prevent and promptly manage extravasation. The concentrated formulation requires dilution.

Contraindications and cautions

• Hypersensitivity to phenylephrine or formulation excipients.
• For selected injections: severe hypertension, severe hyperthyroidism or significant peripheral vascular disease.
• For selected high-strength eye drops: cardiovascular disease, hypertension, aneurysm, tachycardia, thyrotoxicosis, long-standing insulin-dependent diabetes and susceptible narrow-angle glaucoma.
• For oral capsules: cardiovascular disease, hypertension, diabetes, closed-angle glaucoma, hyperthyroidism, prostatic enlargement and phaeochromocytoma.
• Concurrent or recent monoamine oxidase inhibitor use; exact restrictions are product-specific.

Monitoring

• Monitor blood pressure and heart rate during intravenous treatment.
• Monitor cardiac rhythm and organ perfusion in patients with cardiovascular disease or reduced cardiac output.
• Observe the intravenous site for blanching, pain, leakage or tissue ischaemia.
• After eye administration, remain alert for marked hypertension, arrhythmia or acute angle-closure symptoms.

Clinical pharmacology

Phenylephrine is a predominantly alpha-1-adrenoceptor agonist. Vasoconstriction increases systemic vascular resistance and blood pressure, but can reduce cardiac output and trigger reflex bradycardia. In the eye it produces pupil dilation with minimal cycloplegia; orally it reduces nasal mucosal swelling.

Formulation and product differences

• The oral capsule contains lactose.
• The selected eye-drop product is a preservative-free sterile single-use unit containing sodium metabisulphite and has age- and cardiovascular-specific restrictions.
• The ready-to-use injection is a clear intravenous solution.
• The concentrated injection must be diluted before intravenous administration and protected from light.

Eye drops

Route: Ophthalmic

Strengths: 2.5% w/v, 10% w/v

Capsule

Route: Oral

Strengths: 12.2 mg

Injection

Route: Parenteral

Strengths: 50 micrograms/mL, 100 micrograms/mL, 0.1 mg/mL, 10 mg/mL