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Phenylephrine (By injection)

Phenylephrine (fen-il-EF-rin)

Treats low blood pressure during surgery, shock, or an allergic reaction.

Brand Name(s):

Neo-Synephrine HCl, Vazculep

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. You should not receive it if you had an allergic reaction to phenylephrine.

How to Use This Medicine:


  • A nurse or other health provider will give you this medicine. It is given as a shot under your skin, into a muscle, or into a vein.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Some medicines can affect how phenylephrine works. Tell your doctor if you are using amiodarone, aldosterone, atomoxetine, atropine, chlorpromazine, clonidine, guanfacine, hydrocortisone, methylergonovine, nifedipine, reserpine, an MAO inhibitor (MAOI), or a tricyclic antidepressant.

Warnings While Using This Medicine:

  • Tell your doctor if you are pregnant or breastfeeding, or if you have kidney disease, liver disease, asthma, heart or blood vessel problems (such as heart failure, peripheral vascular disease, slow heartbeat), an overactive thyroid, or a history of angina. Tell your doctor if you have an allergy to sulfite medicines.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Chest pain, trouble breathing
  • Fast, slow, or uneven heartbeat
  • Redness, pain, or discoloration at the injection site
  • Tingling in your hands or feet

If you notice these less serious side effects, talk with your doctor:

  • Anxiety or restlessness
  • Headache

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 6/18/2019

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