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

• Pre-Intubation 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

• Allergy to class/drug

Adverse Reactions

• Baroreceptor-mediated reflex bradycardia
• If extravasates use phentolamine

Pharmacology

• Half-life:
• Metabolism:
• Excretion:
• 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

Indication

• Neurogenic Shock
• Second line agent for septic shock

See Also

http://www.atsjournals.org/doi/abs/10.1164/rccm.201006-0972CI?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed#readcube-epdf