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Cloxacillin (penicillin-derivative antibiotic)

Written by Stephanie Nera, RPh, PharmD · Pharmacology

Updated Jun 25, 2021

Cloxacillin is used to treat several types of bacterial infections. Cloxacillin is a type of penicillin antibiotic. It works by targeting the bacterial cell wall which inhibits bacterial cell growth and leads to bacterial cell death.

This antibiotic treats only bacterial infections. Cloxacillin will not work for viral infections (e.g., common cold, flu). Unnecessary use or overuse of any antibiotic can lead to its decreased effectiveness.


Know the basics

What is cloxacillin used for?

  • Benzylpenicillin-resistant Staphylococcus infections
  • Endocarditis
  • Septic arthritis
  • Septicemia
  • Skin and soft tissue infections
  • How should I take cloxacillin?

    Swallow oral tablets or capsules whole without chewing, crushing, or opening. Take it on an empty stomach, either 1 to 2 hours before meals or 2 to 3 hours after meals.

    If you are using an oral suspension, add the appropriate amount of water and shake the bottle well before each dose. Only use a medical-grade measuring cup for each dose, not a household spoon.

    Parenteral (e.g. IV) forms should be administered by a licensed healthcare professional.

    Always complete all the days and doses of your antibiotic treatment, even if you feel better. Stopping early might allow the infection to return and the bacteria may become resistant to antibiotics.

    How do I store cloxacillin?

    This product is best stored at room temperature away from direct light and moisture. Reconstituted suspensions should be stored in the refrigerator for up to 14 days. To prevent drug damage, you should not store it in the bathroom or the freezer. 

    There may be different brands of this drug that may have different storage needs. So, it is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

    You should not flush this product down the toilet or pour them into a drain unless instructed to do so. Additionally, it is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

    Know the precautions & warnings

    What should I know before using cloxacillin?

    Before using this drug, tell your doctor if you are/have:

    • Pregnant or breastfeeding.
    • Taking any other medicines. This includes any prescription, OTC, and herbal remedies.
    • An allergy to any of the ingredients of this product.
    • Any other illnesses, disorders, or medical conditions.

    Is it safe to take cloxacillin during pregnancy or breast-feeding?

    Unfortunately, there isn’t enough information about the safety of using this drug during pregnancy and breastfeeding. However, it is likely safe to take. Please always consult with your doctor to weigh the potential benefits and risks before taking any medication.

    This medication is pregnancy risk category B according to the US Food and Drug Administration (FDA).

    FDA pregnancy risk category reference below:

    • A=No risk
    • B=No risk in some studies
    • C=There may be some risk
    • D=Positive evidence of risk
    • X=Contraindicated
    • N=Unknown

    Know the side effects

    What are the side effects of cloxacillin?

    Like all drugs, this product may have side effects. If they occur, side effects are generally mild and resolve once treatment is finished or the dose is lowered. Some reported side effects include:

    • Allergic reaction
    • Bleeding or bruising
    • Diarrhea
    • Nausea, vomiting
    • Abdominal pain
    • Increased risk of opportunistic infections
    • Seizure
    • Confusion
    • Anaphylactic reaction **potentially fatal

    However, not everyone experiences these side effects. In addition, some people may experience other side effects. So, if you have any concerns about a side effect, please consult your doctor or pharmacist.

    Know the interactions

    What drugs may interact with cloxacillin?

    This medication may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. 

    To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. 

    Drugs with known interactions:

    • Probenecid
    • Methotrexate
    • Warfarin, vitamin K antagonists
    • Tetracyclines

    If you experience an adverse drug interaction, inform your doctor immediately to reevaluate your treatment plan. Approaches include dose adjustment, drug substitution, or ending therapy.

    Does food or alcohol interact with cloxacillin?

    This drug may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. It is best to take it on an empty stomach because food can affect drug absorption. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

    What health conditions may interact with cloxacillin?

    This drug may interact with underlying conditions. This interaction may worsen your health condition or alter the way the drug works. Therefore, it is important to always let your doctor and pharmacist know all the health conditions you currently have.

    Understand the Dosage

    The information provided is not a substitute for any medical advice. Therefore, you should always consult with your doctor or pharmacist before using any medication.

    What is the dose for an adult?

    Susceptible infections

    • Oral: Take 250 to 500 mg every 6 hours, up to 6 g per day.
    • Via IM/IV injections: Administer 250 to 500 every 6 hours, up to 6 g per day.

    What is the dose for a child?

    Susceptible infections

    • Oral: Children weighing 20 kg or less should receive 25 to 50 mg per kg per day every 6 hours. Children over 20 kg should receive the same dose as adults.
    • Via IM/IV injections: Children weighing 20 kg or less should receive 25 to 50 mg per kg per day every 6 hours. Children over 20 kg should receive the same dose as adults.

    How is cloxacillin available?

    Cloxacillin is available in the following dosage forms and strengths:

    • Capsule 250 mg, 500 mg
    • Powder for injection 250 mg, 500 mg
    • Oral suspension (powder) 125 mg/5mL, 250 mg/5mL

    What should I do in case of an emergency or overdose?

    In case of an emergency or an overdose, call your local emergency services or go to the nearest emergency room.

    What should I do if I miss a dose?

    If you miss a dose, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose. Avoid missing doses to prevent antibiotic resistance and treatment failure.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Written by

    Stephanie Nera, RPh, PharmD


    Updated Jun 25, 2021

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