Phenylephrine (Neosynephrine)

Anesthesia Implications

Classification: Alpha-1 agonist, Vasopressor, Sympathomimetic
Therapeutic Effects: Raises blood pressure/treats hypotension
Time to Onset: 30-60 seconds
Time to Peak: 1-2 minutes
Duration: 15-20 minutes

Contraindications

Bradycardia, pheochromocytoma, hypertension,

Primary Considerations

Used as one of the first-line treatments of intraoperative hypotension. Often causes a baroreceptor reflex (which can lead to bradycardia). For this reason, if the patient has bradycardia, an agent such as ephedrine would be considered. Avoided in patients having flap/skin surgery as it reduces perfusion to the new flap. Use is rare with pediatric patients.
Phenylephrine is just as effective as ephredrine at maintaining placental perfusion. Recent evidence suggests that infants had less acidosis when the mothers hypotension was treated with phenylephrine (versus ephedrine).

IV push dose

40 – 100 mcg is the typical starting dose. Needs to be titrated to effect. This drug usually comes in a 10 mg vial and has to be diluted. Typical dilution is as follows for the 10mg (1ml) vial:
Add the contents of the vial to a 100ml saline bag to dilute to 100 mcg/ml.
Add the contents of the vial to a 250ml saline bag to dilute to 40 mcg/ml.

Peds: 0.5-10 mcg/kg (rare use)

IV infusion dose

40-80 mcg/min START, titrated to effect. 100-200 mcg/min is the higher end of the spectrum. Peds: 0.1-0.5 mcg/kg/min (rare use)

Method of Action

Vasoconstrictor of both arterial and venous blood vessels

Metabolism

Hepatic