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Septrin (co-trimoxazole, antibacterial agent)

Written by Stephanie Nera, RPh, PharmD · Pharmacology

Updated Jul 06, 2021

Septrin is the brand name of the drug co-trimoxazole. Co-trimoxazole is a combination of two antibacterial agents: sulfamethoxazole and trimethoprim (SMZ-TM). It is only available with a physician’s prescription.


What is Septrin used for?

Typical and off-label uses include:

  • Urinary tract infection (UTI)
  • Chronic bronchitis
  • Pneumocysti pneumonia (PCP) treatment and prophylaxis
  • Bite wounds
  • Cyclosporiasis
  • Diabetic food infection
  • Epididymitis
  • Donovanosis
  • Intracranial abscess
  • Meningitis
  • Nocardiosis
  • Osteomyelitis
  • Peritonitis
  • Prostatis
  • Prosthetic joint infection
  • Q fever
  • Skin  and soft tissue infections
  • Toxoplasma gondii encephalitis
  • How should I take Septrin?

    Read the directions on the packaging for complete information. Check the label and expiration date.

    For oral dosage forms, swallow it whole without chewing, crushing, or dissolving it in liquid. Oral suspensions should be reconstituted with water before being taken. Shake well and use a medical-grade measuring cup for each dose. Take it with meals.

    For parenteral dosage forms, only a licensed healthcare professional should administer it.

    How do I store Septrin?

    Store this product at room temperature away from direct light and moisture. 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.

    Precautions & Warnings

    What should I know before using Septrin?

    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, especially sulfonamides.
    • Any other illnesses, disorders, or medical conditions.

    Is it safe during pregnancy or breastfeeding?

    This drug can affect a fetus or baby during pregnancy and breastfeeding. Both drugs pass the placenta and into breast milk. Theoretically, sulfonamides can cause kernicterus in newborns, especially in the third trimester. Please always consult with your doctor to weigh the potential benefits and risks before taking any medication.

    This medication is pregnancy risk category D 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

    Side Effects

    What side effects can occur from Septrin?

    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:

    • Hyperkalemia
    • Palpitations
    • Thrush
    • Headache
    • Nausea
    • Diarrhea
    • Skin rashes
    • Breathing problem
    • Fainting
    • Swelling
    • Chest pain

    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.


    What drugs may interact with Septrin?

    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:

    • Creatinine
    • Zidovudine
    • Warfarin
    • Digoxin

    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 Septrin?

    This drug may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

    What health conditions may interact with Septrin?

    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.


    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?

    Adults and children over 12 years:

    The recommended dose is two tablets every 12 hours.

    This dosage approximates to 6 mg trimethoprim and 30 mg sulfamethoxazole per kilogram body weight per 24 hours.

    What is the dose for a child?

    For children 2 months and older, give 6 to 12 mg (based on TMP) per kg of body weight each day. Doses should be divided into every 12 hours given orally or through IV. The maximum single dose is 160 mg of TMP.

    How is Septrin available?

    Septrin is available in the following dosage forms and strengths:

    • Oral suspension containing 200 mg sulfamethoxazole and 40 mg trimethoprim per 5 mL
    • Tablets 400 mg SMZ and 80 mg TM, 800 mg SMZ and 160 mg TM
    • Solution for injection 80 mg SMZ and 16 mg TM

    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 Jul 06, 2021

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