Phenylephrine

General

  • Type: Vasopressors
  • Dosage Forms:
  • Common Trade Names: Neosynephrine

Adult Dosing

Hypotension

  • Start 100-200 mcg/min then taper down
    • 40-60 mcg/min works for most
  • "Push dose"
    • Inject 1ml (10mg) into 100ml NS Bag = 100mcg/ml
    • Draw this into a syringe, each ml is 100mcg
    • Give in 0.5-2ml (50-200mcg) alloquots q2-5min

Low Flow Priapism

  • Dilute phenylephrine 1mg in 9mL NS for final concentration of 100mcg/mL
    • For 500 mcg/ml, take 0.5 ml of 10mg/ml phenylephrine, and dilute in 9.5 cc NS
  • Inject base of penis with 29-Ga needle (after blood aspiration to confirm position)
    • 100-500 mcg every 3-5min (max 1000 mcg) until resolution or 1 hour

Pediatric Dosing

  • Hypotension/Shock
    • IV Bolus: 5-20mcg/kg q10-15min prn, 1st dose should not exceed 500mcg with a max dose of 1000mcg
    • IV Infusion: 0.1-0.5mcg/kg/min, titrate to desired BP
  • Nasal Congestion (OTC)
    • 4-<6yrs: 2.5mg q4hr prn for <7 days
    • 6-<12yrs: 5mg q4hr prn for <7 days

Special Populations

  • Pregnancy Rating: C
  • Lactation: infant risk cannot be ruled out
  • Renal Dosing
    • Adult
    • Pediatric
  • Hepatic Dosing
    • Adult
    • Pediatric

Contraindications

Adverse Reactions

  • Baroreceptor-mediated reflex bradycardia, particularly in patients with preexisting cardiac dysfunction or severe CAD
  • If extravasates use phentolamine

Serious

Common

Pharmacology

  • Half-life: 2-3h
  • Metabolism: extensively in intestinal wall, moderately in liver
  • Excretion: Urinary
  • Mechanism of Action: selective α1 agonist causes vasoconstriction

Primary Receptor

  • α1

Relative Effects

  • ↑SVR
  • ↓HR (reflex bradycardia)

Notes

  • Use with caution in patients with spinal cord injury-related bradycardia
  • Useful for treatment of vasodilatory shock when norepinephrine or dopamine have precipitated tachyarrhythmias
  • In patients with ↓LV function, unopposed α1 may lead to decreased CO or myocardial ischemia
    • However clinical trials do not support these effects when used in clinically appropriate dose range
  • Commonly used as an alternative to norepinephrine in the setting of atrial fibrillation with rapid ventricular response (associated with lower heart rate after initiation of vasopressor) [1]

Indication

  • Neurogenic Shock
  • Second line agent for septic shock

See Also

References

  1. Law AC, Bosch NA, Peterson D, Walkey AJ. Comparison of Heart Rate After Phenylephrine vs Norepinephrine Initiation in Patients With Septic Shock and Atrial Fibrillation. Chest. 2022;162(4):796-803. doi:10.1016/j.chest.2022.04.147