Phenylephrine
General
- Type: Vasopressors
- Dosage Forms: Commonly 50 mg per 5 mL (10 mg/mL)
- Common Trade Names: Neosynephrine
- Onset of action: About 1 minute
- Duration of action: 10-20 minutes
Adult Dosing
Hypotension
- Start 100-200 mcg/min then taper down
- 40-60 mcg/min works for most
- "Push dose"
- Inject 1 mL (10 mg) into 100 mL NS Bag = 100 mcg/mL
- Draw this into a syringe, with a concentration of 100mcg/mL
- Administer 0.5-2 mL (50-200 mcg) every 2-5 minutes
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
- Allergy to class/drug
- Severe hypertension
- Ventricular tachycardia
- Closed angle glaucoma
- Caution if:
- Heart failure or cardiogenic shock (cardiac output may decrease with increased SVR)
- Spinal cord injury or other autonomic dysfunction (may experience exaggerated increase in blood pressure)
- Hyperthyroidism
Adverse Reactions
- Baroreceptor-mediated reflex bradycardia, particularly in patients with preexisting cardiac dysfunction or severe CAD
- If extravasates use phentolamine
Serious
- Bradycardia
- Pulmonary edema
- Metabolic acidosis
- Decreased renal perfusion
- Extravasation
Common
- Hypertension
- Anxiety
- Headache
- Rebound congestion, sneezing
- Nausea, gastric irritation
Pharmacology
- Half-life: 2.5 hours
- 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
- ↑ 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