This medication is used to treat a wide variety of bacterial infections. This medication is known as a penicillin-type antibiotic. It works by stopping the growth of bacteria.

This medication is given by injection into a vein as directed by your doctor, usually every 4 to 6 hours. The dosage is based on your medical condition and response to treatment. Children's dosage is also based on weight.

If you are giving this medication to yourself at home, learn all preparation and usage instructions from your health care professional. Before using, check this product for particles or discoloration. If either is present, do not use the liquid. Learn how to store and discard medical supplies safely.

If you are using the frozen pre-mixed solution, thaw the medication at room temperature or in the refrigerator. If the container is thawed in the refrigerator, let it come to room temperature before using. Do not thaw by putting in a water bath or microwave. After thawing, shake well and squeeze the container to check for leaks. Discard the solution if the container leaks. Do not re-freeze the solution after thawing.

Give aminoglycosides (such as gentamicin) separately from this medication. Do not mix together in the same IV fluid.

For the best effect, use this antibiotic at evenly spaced times. To help you remember, use this medication at the same time(s) every day.

Continue to use this medication until the full prescribed amount is finished, even if symptoms disappear after a few days. Stopping the medication too early may result in a return of the infection.

Tell your doctor if your condition lasts or gets worse.

If this medication is injected into a muscle, pain at the injection site may occur. If this effect lasts or gets worse, notify your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• pain/swelling/skin peeling at injection site (if this drug is injected into a vein)
• joint/muscle pain
• signs of kidney problems (such as change in the amount of urine, pink/bloody/frothy/dark/cloudy urine)
• extreme tiredness
• easy bruising/bleeding
• new signs of infection (such as sore throat that doesn't go away, fever)
• seizures
• uncontrolled movements
• confusion
• irregular heartbeat
• muscle cramps
• weakness

This medication may rarely cause a severe intestinal condition due to a bacteria called C. difficile. This condition may occur during treatment or weeks to months after treatment has stopped. Tell your doctor right away if you develop:

• diarrhea that doesn't stop
• abdominal or stomach pain/cramping
• blood/mucus in your stool

If you have these symptoms, do not use anti-diarrhea or opioid products because they may make symptoms worse.

Use of this medication for prolonged or repeated periods may result in oral thrush or a new vaginal yeast infection. Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before using this medication, tell your doctor or pharmacist if you are allergic to it; or to penicillin or cephalosporin antibiotics; or if you have any other allergies. This product may contain inactive ingredients (such as corn for products containing dextrose), which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• asthma
• kidney disease
• liver disease

This medication contains sodium. This could affect you if you are on a salt-restricted diet or if you have a condition which could be worsened with an increase in salt intake (such as heart failure). Consult your doctor or pharmacist for more information.

Nafcillin may cause live bacterial vaccines (such as typhoid vaccine) to not work well. Tell your health care professional that you are using nafcillin before having any immunizations/vaccinations.

Older adults may be at greater risk for side effects while using this drug.

Newborns and infants may be a greater risk for side effects while using this drug.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This drug passes into breast milk. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include:

• "blood thinners" (such as warfarin)
• methotrexate
• tetracyclines

This medication can speed up the removal of other medications from your body, which may affect how they work. Examples of affected drugs include daridorexant, elacestrant, certain products used to treat chronic hepatitis C (asunaprevir, ombitasvir/paritaprevir/ritonavir), mavacamten, quizartinib, revumenib, among others.

This medication may decrease the effectiveness of hormonal birth control such as pills, patch, or ring. This could cause pregnancy. Discuss with your doctor or pharmacist if you should use reliable backup birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well.

This medication may interfere with certain lab tests (such as urine protein tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669. Symptoms of overdose may include: seizures, confusion, mental/mood changes (such as agitation).

Lab and/or medical tests (such as kidney/liver function, complete blood count) may be done while you are using this medication. Keep all medical and lab appointments. Consult your doctor for more details.

It is important to get each dose of this medication as scheduled. If you miss a dose, ask your doctor or pharmacist right away for a new dosing schedule. Do not double the dose to catch up.

Consult the product instructions and your pharmacist for storage details. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.