What Is Phenylephrine and How Does It Work?

Phenylephrine is an alpha-1 adrenergic receptor agonist indicated for the treatment of clinically important hypotension resulting primarily from vasodilation in the setting of anesthesia.

Phenylephrine is available under the following different brand names: Vazculep.

Dosages of Phenylephrine

Adult and Pediatric Dosage Forms and Strengths

Injectable solution

  • 10 mg/mL

Dosage Considerations – Should be Given as Follows:

Mild to Moderate Hypotension


  • Initial: 2-5 mg intramuscularly (IM) or subcutaneously (SC); not to exceed 5 mg
  • Maintenance: 1-10 mg


  • 5-20 mcg/kg intravenous (IV) bolus every 10-15 minutes as needed, OR
  • 0.1-0.5 mcg/kg/min IV continuous infusion

Severe Hypotension/Shock

  • 100-180 mcg increments intravenous (IV) bolus, THEN
  • 40-60 mcg/min continuous IV infusion

What Are Side Effects Associated with Using Phenylephrine?

Common side effects of phenylephrine include:

  • Leakage of intravenous medication
  • Hypertension
  • Slow heart rate
  • Anxiety
  • Headache
  • Burning
  • Rebound congestion
  • Sneezing
  • Excess fluid in the lungs (pulmonary edema)
  • Metabolic acidosis
  • Decreased blood flow to the kidneys
  • Reduced urine output
  • Nausea
  • Stomach pain or upset

This is not a complete list of side effects and other serious side effects may occur. Call your doctor for information and medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Phenylephrine?

If your doctor has directed you to use this medication for your condition, your doctor or pharmacist may already be aware of any possible drug interactions or side effects and may be monitoring you for them. Do not start, stop, or change the dosage of this medicine or any medicine before getting further information from your doctor, healthcare provider or pharmacist first.

  • Severe Interactions of phenylephrine include:
  • 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:

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Phenylephrine?


Physicians should completely familiarize themselves with complete contents of package insert prior to prescribing phenylephrine hydrochloride injection.

This medication contains phenylephrine. Do not take Vazculep if you are allergic to phenylephrine or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


Effects of Drug Abuse

  • No information available

Short-Term Effects

  • See "What Are Side Effects Associated with Using Phenylephrine?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Phenylephrine?"


Pregnancy and Lactation

  • Use phenylephrine with caution during pregnancy if benefits outweigh risks. Animal studies show risk and human studies are not available, or neither animal nor human studies were done.
  • Phenylephrine is considered safe to use while breastfeeding. Consult your doctor.
Medscape. Phenylephrine.
DailyMed. Vazculep.

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