α1-adrenoceptor agonist (vasopressor) Pregnancy: SPC 4.6: animal studies are insufficient with respect to reproductive toxicity and teratogenicity. Use of injectable phenylephrine is possible during pregnancy in accordance with the indications. Administration in late pregnancy or labour may potentially cause fetal hypoxia and bradycardia; combination with some oxytocic agents can cause severe hypertension. Breast-feeding: small quantities are excreted into human breast milk and oral bioavailability may be low - after a single bolus administration during childbirth, breast-feeding is possible.

Phenylephrine hydrochloride

Brand names: Boots Decongestant, Sudafed PE

Phenylephrine hydrochloride is a selective alpha-1 adrenergic agonist used parenterally as a vasopressor to treat hypotension, including spinal/epidural anaesthesia-induced and other peri-operative hypotension.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Intravenous bolus injection: 50 to 100 micrograms, which can be repeated until the desired effect is attained. Continuous intravenous infusion: initial dose 25 to 50 micrograms/min.

Route: Parenteral administration - intravenous bolus injection or intravenous infusion

Frequency: Bolus may be repeated until the desired effect is attained; the infusion rate may be increased or decreased to maintain the systolic blood pressure close to the normal value

Max: One bolus dose should not exceed 100 micrograms. Infusion doses between 25 and 100 micrograms/min have been assessed to be effective.

Units are exactly as stated in SPC 4.2 - micrograms per bolus and micrograms/min for infusion (NOT per kg). Hepatic impairment: higher doses of phenylephrine may be needed in patients with cirrhosis of the liver. Older people: treatment of the elderly should be carried out with care; SPC 4.8 notes the risk of phenylephrine toxicity is increased in elderly patients. Paediatric population: the safety and efficacy of phenylephrine in children have not been established and no data are available. SPC 4.4: arterial blood pressure should be monitored during treatment; consider dose reduction in patients with reduced cardiac output or coronary vascular disease when systemic blood pressure is near the lower end of the target range; particular attention should be paid to avoid extravasation, since this may cause tissue necrosis. Should only be administered by healthcare professionals with appropriate training and relevant experience. Product fetched: Phenylephrine 0.1 mg/ml solution for injection; the SPC text also refers to the 50 micrograms/ml and 100 micrograms/ml solution for injection strengths.

Dose adjustments

Renal

Lower doses of phenylephrine may be needed in patients with impaired renal function (SPC 4.2). No numeric adjustment is specified.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Severe hypertension or peripheral vascular disease, due to the risk of ischaemic gangrene or vascular thrombosis
In combination with non-selective monoamine oxidase inhibitors, or within 2 weeks of their withdrawal, due to the risk of paroxysmal hypertension and possibly fatal hyperthermia
Severe hyperthyroidism

Side effects

Reflex bradycardia - the most commonly reported cardiovascular adverse event (frequency not known)
Hypertension and hypertensive crisis; hypertension is more frequent with high doses (frequency not known)
Nausea and vomiting (frequency not known)
Tachycardia, palpitations, arrhythmia, angina pectoris, myocardial ischaemia (frequency not known)
Headache, nervousness, insomnia, paraesthesia, tremor; anxiety, excitability, agitation, confusion (frequency not known)
Skin necrosis with extravasation, pallor or skin blanching, sweating (frequency not known)

Interactions

Non-selective monoamine oxidase inhibitors (iproniazid, nialamide) - contraindicated; paroxysmal hypertension and possibly fatal hyperthermia, still possible 15 days after discontinuation of the MAOI
Selective type A monoamine oxidase inhibitors (moclobemide, toloxatone) and linezolid - inadvisable; risk of vasoconstriction and/or hypertensive crisis
Dopaminergic ergot alkaloids (bromocriptine, cabergoline, lisuride, pergolide) and vasoconstrictor ergot alkaloids (dihydroergotamine, ergotamine, methylergometrine, methysergide) - inadvisable; risk of vasoconstriction and/or hypertensive crisis
Tricyclic antidepressants (e.g. imipramine) - inadvisable; paroxysmal hypertension with possibility of arrhythmias
Noradrenergic-serotoninergic antidepressants (milnacipran, venlafaxine) - inadvisable; paroxysmal hypertension with possibility of arrhythmias
Guanethidine - listed in SPC 4.5 (source text truncated at this entry; review the full section 4.5)
Some oxytocic agents - the combination can cause severe hypertension (SPC 4.6)

Clinical monograph

How it works

It stimulates peripheral alpha-1 adrenoceptors to cause vasoconstriction, raising systemic vascular resistance and blood pressure; the resulting rise in afterload often produces a reflex (vagally mediated) bradycardia.

Prescribing in practice

Reflex bradycardia is common as blood pressure rises, and extravasation of the more concentrated solutions can cause tissue ischaemia and necrosis, so give via a secure cannula and monitor the infusion site.
Use with caution in hypertension, hyperthyroidism, ischaemic heart disease and severe coronary or peripheral arterial disease, where excessive vasoconstriction may be harmful.
Marked pressor response and hypertensive crisis can occur in patients taking monoamine oxidase inhibitors or with other sympathomimetics, so review concurrent therapy before use.

Monitoring

Monitor blood pressure and heart rate continuously during parenteral administration, titrating to the target pressure.

Counselling the patient

Explain to the team that this is a vasopressor given to support blood pressure and that pulse and pressure are being watched closely.
Report any pain, swelling or colour change at the drip site promptly as this may indicate the drug has leaked from the vein.

Evidence & guidelines

Phenylephrine is widely recommended for managing hypotension during spinal anaesthesia, particularly in obstetric practice where it helps preserve umbilical cord pH compared with some alternatives.

Reference: AAGBI; SSC 2021; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Pathways

📚 MRCEM Revision

Featured in these MRCEM clinical pathways

Phenylephrine hydrochloride is a core drug in the following exam-focused workups on our sister siteReviseMRCEM.

Acute Red Eye

MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.