Medically Reviewed on 8/17/2022

Generic Name: phenylephrine

Brand Names: Vazculep, Biorphen

Drug Class: Alpha1 Agonists

What is phenylephrine, and what is it used for?

Phenylephrine is a medication used in clinical settings for the treatment of low blood pressure (hypotension) resulting primarily from blood vessel dilation (vasodilation) during anesthesia.

Phenylephrine is administered intravenously to increase blood pressure back to normal levels, after withdrawal of anesthesia. Phenylephrine increases blood pressure by constricting peripheral blood vessels.

Phenylephrine belongs to a class of medications known as alpha1 agonists and works by stimulating the activity of alpha1 adrenergic receptors. Alpha1 adrenergic receptors are protein molecules located in many smooth muscle tissues including blood vessels, heart muscle and bladder neck, which make these smooth muscles contract when stimulated. The contraction of vascular smooth muscles constricts the blood vessels, increasing vascular resistance to blood flow, which results in a rise in blood pressure.


  • Phenylephrine can precipitate chest pain (angina) in patients with narrowed arteries (arteriosclerosis), worsen congestive heart failure and increase pulmonary arterial pressure, use with caution.
  • Phenylephrine can slow heart rate (bradycardia) and reduce cardiac output. Use with caution in patients with preexisting bradycardia, partial heart block, heart muscle (myocardial) disease or severe coronary artery disease.
  • Avoid phenylephrine or use it with extreme caution in patients with heart failure or cardiogenic shock. Cardiac output may decrease with increase in systemic vascular resistance and blood pressure.
  • Phenylephrine can cause excessive vasoconstriction and impair blood flow to vital organs. Use with caution in patients with extensive peripheral vascular disease.
  • Phenylephrine can increase the need for renal replacement therapy in patients with septic shock. Monitor kidney function.
  • Patients with spinal cord injury or autonomous nervous system dysfunction may have an exaggerated increase in blood pressure in response, monitor closely.
  • Drugs that stimulate uterine activity (oxytocic drugs) can potentiate the blood pressure raising effect of phenylephrine and increase the risk for hemorrhagic stroke.
  • Some formulations contain sodium metabisulfite that may cause allergic-type reactions, including severe reactions (anaphylaxis) and life-threatening or less severe asthmatic episodes in certain susceptible individuals. Use with extra caution in patients with asthma.
  • Avoid extravasation of the drug from the vein during IV administration, it can damage the surrounding tissue.

What are the side effects of phenylephrine?

Common side effects of phenylephrine include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

  • Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
  • Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
  • Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
  • Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.


Low Blood Pressure (Hypotension): Symptoms, Signs, Causes See Slideshow

What are the dosages of phenylephrine?

Injectable IV Solution (Ready-to-use)

  • 0.1 mg/mL (Biorphen)
  • Do not dilute further

Injectable IV Solution (Concentrated)

  • 10 mg/mL (Vazculep, Biorphen)
  • Requires further dilution


Severe Hypotension/Shock

  • IV bolus: 40-100 mcg every 1-2 minutes as needed, not to exceed total dose of 200 mcg
  • Adjust dosage according to blood pressure goal
  • Continuous IV infusion: If blood pressure is below the target goal, start a continuous IV infusion with an infusion rate of 10-35 mcg/minute; not to exceed 200 mcg/min

Dosage Modifications

Renal impairment

  • Mild-to-moderate: Consider starting at the lower end of the recommended dose range, and adjusting dose based on the target blood pressure goal
  • End-stage renal disease (ESRD): Dose-response data indicate increased responsiveness to phenylephrine

Hepatic impairment

  • Start dosing in the recommended dose range, but more phenylephrine may be needed in this population
  • Moderate-to-severe (Child-Pugh Class B or C): Dose-response data indicate decreased responsiveness to phenylephrine

Dosing considerations

  • Drug not recommended by The Society of Critical Care Medicine, to treat septic shock, except when first line agent epinephrine associated with causing serious arrhythmia, when cardiac output is high and blood pressure persistently low, or when combination of inotrope/vasopressor and low dose vasopressin failed to achieve desired mean arterial pressure and phenylephrine used as salvage therapy


Severe Hypotension/Shock (Off-label)

Children below 2 years

  • Safety and efficacy not established

Children 2 years and above

  • 5-20 mcg/kg IV once; THEN 0.1-0.5 mcg/kg/min IV; not to exceed 3-5 mcg/kg/min IV 


  • Phenylephrine overdose can rapidly increase blood pressure causing symptoms that include headache, vomiting, high blood pressure (hypertension), reflex drop in heart rate (bradycardia), a sensation of fullness in the head, tingling of the extremities, and irregular heart rhythms (cardiac arrhythmias) including ventricular extra beats (extrasystoles) and ventricular rapid beat (tachycardia).
  • There is no antidote for intravenous phenylephrine. Treatment includes discontinuation of the drug, medications to reduce pressure and heart rate, and supportive care.

What drugs interact with phenylephrine?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Severe interactions of phenylephrine include:
    • iobenguane I 123
    • isocarboxazid
    • linezolid
    • phenelzine
    • procarbazine
    • selegiline transdermal
    • tranylcypromine
  • Phenylephrine has serious interactions with at least 31 different drugs.
  • Phenylephrine has moderate interactions with at least 180 different drugs.
  • Mild interactions of phenylephrine include:

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • Data from clinical trials and analyses with use of phenylephrine injection in pregnant women during Cesarean section have not established a drug-associated risk of major birth defects and miscarriage.
  • There are no data, however, on phenylephrine use in first and second trimesters, and animal reproductive studies show evidence of fetal malformations.
  • Hypotension during pregnancy must be treated. Untreated hypotension associated with spinal anesthesia for Cesarean section can increase nausea and vomiting. Reduced blood flow to the uterus due to maternal hypotension can slow the fetal heart rate and cause fetal acidosis.
  • Use phenylephrine during pregnancy with caution, if potential benefits to the mother justify potential risks to the fetus.
  • It is not known if phenylephrine is excreted in breast milk. There are no data on its effects on milk production or the breastfed infant. Decision to breastfeed during therapy should be taken based on mother’s clinical need, benefits of breastfeeding to the infant, and potential risk to the infant from drug exposure or underlying maternal condition.

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Phenylephrine is a medication used in clinical settings for the treatment of low blood pressure (hypotension) resulting primarily from blood vessel dilation (vasodilation) during anesthesia. Common side effects of phenylephrine include headache, nausea, vomiting, gastric pain and irritation, high blood pressure (hypertension), hypertensive crisis, reflex reduction in heart rate (bradycardia), reduced cardiac output, reduced blood flow to tissues (ischemia), irregular heart rhythm (arrhythmia), rebound congestion, decreased kidney perfusion, reduced urine output, fluid in lungs (pulmonary edema), shortness of breath (dyspnea), and others.

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You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Medically Reviewed on 8/17/2022