Phenylephrine

Last updated 27/04/19

Definition

Potent alpha-1 adrenergic vasoconstrictor

Features

No chronotropic or inotropic effects
Cardiovascular effects typically not seen unless given parenterally
Metabolised by liver
Excreted in urine
T/2 2-3.5hrs

Mechanism

Alpha-1 adrenoreceptor: sympathomimetic

Vasopressor: increased systolic and diastolic blood pressure

Increased peripheral resistance (PVR)
Renal, splanchnic, cutaneous, and limb blood flow reduced

Respiratory vascular smooth muscle contraction

Nasal mucosal vasoconstriction
Increased pulmonary artery pressure

Coronary blood flow increased

Indications

Hypotension

Supraventricular Tachycardia (SVT) (old indication due to reflex bradycardia)
Nasal congestion

Dose

IV, IM, S/C, intrathecal, intranasal, PO, eye drops

Ampules: 10mg/ml in 1ml

Clear colorless solution

IV

100-500mcg boluses every 15 minutes
Duration up to 20 minutes
Infusion: Spinal anaesthesia for Caesarean section (LUSCS)

10mg into 500ml Dextrose 5% or saline 0.9% (20mcg/ml)
25-60mcg/minute stable rate
Commence at 100-180mcg/min for rapid correction of hypotension then down titrate

IM/SC

Duration up to 50 minutes

Side Effects/Precautions/Contraindications

Side Effects

Bradycardia: reflex from hypertension
Hypertension
Headache
Restlessness
Overdoes (OD)

Tingling in extremeties
Premature Ventricular Complexes (PVCs)
Short runs of non-sustained Ventricular Tachycardia (VT)

Anaphylaxis

Precautions

Bradycardia may be exacerbated
Oxytocin: may potentiate vasopressor effets
Tricyclic Antidepressants (TCAs) or Monoamine Oxidase Inhibitors (MAOIs)

Contraindications

Severe hypertension
Ventricular Tachycardia (VT)

References