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Nafcillin (injection)

Generic Name: nafcillin (injection) (naf SIL in)
Brand Name: Unipen, Nallpen

Medically reviewed by on Jan 10, 2018 – Written by Cerner Multum

What is nafcillin?

Nafcillin is a penicillin antibiotic that fights bacteria.

Nafcillin is used to treat many different types of infections, especially those caused by staphylococcus bacteria ("staph" infections).

Nafcillin may also be used for purposes not listed in this medication guide.

Important Information

You should not use nafcillin if you are allergic to any penicillin antibiotic.

Before taking this medicine

You should not use this medicine if you are allergic to nafcillin or to any other penicillin antibiotic, such as:

To make sure nafcillin is safe for you, tell your doctor if you have ever had:

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Nafcillin can pass into breast milk and may harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How is nafcillin given?

Follow all directions on your prescription label. Do not use nafcillin in larger or smaller amounts or for longer than recommended.

Nafcillin is injected into a muscle, or into a vein through an IV. You may be shown how to use injections at home. Do not give yourself this medicine if you do not fully understand how to give the injection and properly dispose of used needles, IV tubing, and other items used to inject the medicine.

This medicine must be given slowly, and the infusion can take 30 to 60 minutes to complete.

Nafcillin powder must be mixed with a liquid (diluent) before using it. If you are using the injections at home, be sure you understand how to properly mix and store the medicine.

Your medicine may also be supplied as a premixed solution that has been frozen in a plastic container.

After mixing nafcillin powder with a diluent, store in the refrigerator and use within 7 days.

Mixed medicine must be used within 24 hours if you keep it at room temperature.

Do not use nafcillin if it has changed colors or has particles in it. Call your pharmacist for new medication.

Tell your caregivers if you feel any burning, pain, or swelling around the IV needle when the medicine is injected.

While using nafcillin, you may need frequent blood tests.

This medicine can cause unusual results with certain medical tests. Tell any doctor who treats you that you are using nafcillin.

Use this medicine for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Skipping doses may also increase your risk of further infection that is resistant to antibiotics. Nafcillin will not treat a viral infection such as the flu or a common cold.

Nafcillin is usually given for up to 14 days. Very severe infections may need to be treated for several weeks.

Use a disposable needle and syringe only once. Follow any state or local laws about throwing away used needles and syringes. Use a puncture-proof "sharps" disposal container (ask your pharmacist where to get one and how to throw it away). Keep this container out of the reach of children and pets.

Store unmixed nafcillin powder at room temperature away from moisture and heat.

Store frozen nafcillin in a deep freezer, at -4 degrees Fahrenheit (-20 degrees Celsius).

Take the medicine out of the freezer and allow it to reach room temperature before injecting your dose. Do not use heat to thaw frozen nafcillin.

What happens if I miss a dose?

Use the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not use extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using nafcillin?

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor. Do not use anti-diarrhea medicine unless your doctor tells you to.

Nafcillin side effects

Get emergency medical help if you have signs of an allergic reaction: hives, itching; fever, stomach pain, muscle or joint pain; difficulty breathing; swelling of your face, lips, tongue, or throat.

A delayed allergic reaction to nafcillin can occur as few as 2 days to as many as 4 weeks after you use the medication.

Call your doctor at once if you have:

  • severe stomach pain, diarrhea that is watery or bloody;

  • blood in your urine, urinating less than usual or not at all;

  • severe rash, severe tingling or numbness;

  • blisters or ulcers in your mouth, red or swollen gums, trouble swallowing; or

  • pain, swelling, bruising, or skin changes where the medicine was injected.

Common side effects may include:

  • nausea, vomiting, diarrhea;

  • skin rash;

  • black or "hairy" tongue; or

  • tenderness or irritation around the IV needle.

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

What other drugs will affect nafcillin?

Tell your doctor about all your current medicines and any you start or stop using, especially:

This list is not complete. Other drugs may interact with nafcillin, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.