SIDE EFFECTS: If this medication is injected into a muscle, pain at the injection site may occur. If this effect persists or worsens, notify your doctor or pharmacist promptly. Remember that your doctor has prescribed this medication because he or she 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 (e.g., fever, persistent sore throat), seizures, uncontrolled movements, confusion, irregular heartbeat, muscle cramps, weakness. This medication may rarely cause a severe intestinal condition (Clostridium difficile-associated diarrhea) due to a type of resistant bacteria. This condition may occur during treatment or weeks to months after treatment has stopped. Do not use anti-diarrhea or opioid medications if you have any of the following symptoms because these products may make them worse. Tell your doctor right away if you develop: persistent diarrhea, abdominal or stomach pain/cramping, blood/mucus in your stool. 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.

PRECAUTIONS: 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 (e.g., congestive heart failure). Consult your doctor or pharmacist for more information. Nafcillin may cause live bacterial vaccines (such as typhoid vaccine) to not work as well. Do not have any immunizations/vaccinations while using this medication unless your doctor tells you to. Liver and kidney functions decline as you grow older. This medication is removed by the liver. Therefore, elderly people may be at greater risk for side effects while using this drug. Liver and kidney functions are not fully developed in newborns and infants. This medication is removed by the liver. Therefore, 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 breast-feeding.

DRUG INTERACTIONS: 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" (e.g., 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 certain products used to treat chronic hepatitis C (asunaprevir, ombitasvir/paritaprevir/ritonavir), among others. Although most antibiotics are unlikely to affect hormonal birth control such as pills, patch, or ring, a few antibiotics (such as rifampin, rifabutin) can decrease their effectiveness. This could result in pregnancy. If you use hormonal birth control, ask your doctor or pharmacist for more details. This medication may interfere with certain laboratory tests (including certain urine protein tests), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

OVERDOSE: 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 their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: seizures, confusion, mental/mood changes (e.g., agitation).