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Nafcillin Injection

(naf sil' in)

Brand Name(s): Unipen® Injection; also available generically

Other Name(s): Ethoxynaphthamido Penicillin Sodium, Sodium Nafcillin

WHY is this medicine prescribed?

Nafcillin injection is used to treat infections caused by certain types of bacteria. Nafcillin injection is in a class of medications called penicillins. It works by killing bacteria.

Antibiotics such as nafcillin injection will not work for colds, flu, or other viral infections. Taking antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

Are there OTHER USES for this medicine?

Nafcillin injection is also sometimes used to prevent infection in people who are having certain types of surgery. Talk to your doctor about the risks of using this medication for your condition.

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

HOW should this medicine be used?

Nafcillin injection comes as a powder to be mixed with fluid or as a premixed product and injected intravenously (into a vein). Nafcillin injection can also be given intramuscularly (into a muscle). It is usually given every 4 to 6 hours. The length of your treatment depends on the type of infection you have.

You may receive nafcillin injection in a hospital or you may administer the medication at home. If you will be receiving nafcillin injection at home, your healthcare provider will show you how to use the medication. Be sure that you understand these directions, and ask your healthcare provider if you have any questions.

You should begin to feel better during the first few days of treatment with nafcillin injection. If your symptoms do not improve or get worse, call your doctor.

Use nafcillin injection until you finish the prescription, even if you feel better. If you stop using nafcillin injection too soon or skip doses, your infection may not be completely treated and the bacteria may become resistant to antibiotics.

What SPECIAL PRECAUTIONS should I follow?

Before receiving nafcillin injection,

  • tell your doctor and pharmacist if you are allergic to nafcillin; penicillins; cephalosporin antibiotics such as cefaclor, cefadroxil, cefazolin, cefdinir, cefditoren (Spectracef), cefepime (Maxipime), cefixime (Suprax), cefotaxime (Claforan), cefotetan, cefoxitin (Mefoxin), cefpodoxime, cefprozil, ceftaroline (Teflaro), ceftazidime (Fortaz, Tazicef, in Avycaz), ceftibuten (Cedax), ceftriaxone (Rocephin), cefuroxime (Zinacef), and cephalexin (Keflex); any other medications; or any of the ingredients in nafcillin injection. Ask your pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: other antibiotics; cyclosporine (Gengraf, Neoral, Sandimmune); probenecid (in Col-Probenecid, Probalan); tetracycline (Sumycin); and warfarin (Coumadin, Jantoven). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • tell your doctor if you have or have ever had allergies, asthma, heart failure, or kidney or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while receiving nafcillin injection, call your doctor.

What SPECIAL DIETARY instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

What SIDE EFFECTS can this medicine cause?

Nafcillin injection may cause side effects. Tell your doctor if this symptom is severe or does not go away:

  • diarrhea

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

  • severe diarrhea (watery or bloody stools) that may occur with or without fever and stomach cramps (may occur up to 2 months or more after your treatment)
  • hives, rash, itching, fever, that may occur along with stomach, muscle, or joint pain
  • difficulty swallowing or breathing
  • swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
  • hoarseness
  • dizziness or fainting
  • tenderness, warmth, redness, swelling, or pain near the injection site

Nafcillin injection may cause other side effects. Call your doctor if you have any unusual problems while receiving this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I know about STORAGE and DISPOSAL of this medication?

Your healthcare provider will tell you how to store your medication. Store your medication only as directed. Make sure you understand how to store your medication properly.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

What OTHER INFORMATION should I know?

Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body's response to nafcillin injection.

Before having any laboratory test, tell your doctor and the laboratory personnel that you are receiving nafcillin injection.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

This branded product is no longer on the market. Generic alternatives may be available.


This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists® represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists® makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists® does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

Pronunciation Guide for Drug Names is used with permission. © 2009. The United States Pharmacopeial Convention. All Rights Reserved.

AHFS® Patient Medication Information™. © Copyright, 2020. The American Society of Health-System Pharmacists®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: April 15, 2016.