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
  • 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: 2-3h
  • 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

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

References
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