Septrin (co-trimoxazole) (2023)

What is Septrin?

Septrin is a brand name for the antibiotic medicine co-trimoxazole. This antibiotic is mainly used to prevent a small number of serious infections in people with an underactive immune system, for example people with HIV or AIDS and people having treatment for cancer. In particular it's used to prevent and treat a type of pneumonia called PCP, which is caused by the bacterium Pneumocystis jirovecii, previously known as Pneumocystis carinii. It's also used for toxoplasmosis and a lung infection called nocardiosis.

Less serious infections are sometimes treated with co-trimoxazole if other antibiotics aren't suitable and microscopy and culture show that the bacteria causing the infection are sensitive to co-trimoxazole.

How does co-trimoxazole work?

Co-trimoxazole is a mixture of two different antibiotics, called sulfamethoxazole and trimethoprim. Sulfamethoxazole is a type of antibiotic called a sulfonamide.

These antibiotics work together in different ways to prevent bacteria from producing a substance called folate. Without folate, the bacteria cannot produce DNA and so are unable grow, multiply and increase in numbers. Co-trimoxazole therefore stops the spread of infection. The remaining bacteria are killed by the immune system or eventually die.

Key facts about Septrin

  • Septrin is a brand name for co-trimoxazole.
  • Co-trimoxazole is suitable for adults and children.
  • It's usually taken twice a day to treat infections. To prevent PCP you might be asked to take it every day or three times a week. Keep taking it for as long as your doctor asks you to.
  • It's important to drink plenty of fluid while while you're taking co-trimoxazole.
  • Common side effects include feeling sick, diarrhoea, headache and rash.
  • It's generally OK to drink alcohol in moderation while taking co-trimoxazole. See below.

    Who shouldn't take Septrin?

    Co-trimoxazole may not suitable for people with certain conditions and some people may need extra monitoring or a lower dose. Make sure your doctor knows if you:

    • are pregnant, trying for a baby or breastfeeding
    • have ever had an allergic reaction to a sulfonamide medicine or trimethoprim
    • have asthma or severe allergies
    • have kidney or liver problems
    • have a rare metabolic disorder called porphyria
    • have an enzyme deficiency called G6PD deficiency
    • have problems with your blood cell counts, such as low white blood cells, anaemia or folic acid deficiency
    • have a high level of potassium in your blood.

      How do I take Septrin?

      Septrin (or generic co-trimoxazole) comes as tablets and suspension. It's sometimes given by drip into a vein for more severe infections.

      The Septrin dose prescribed, how often to take it and for how long depends on what you are taking it for. Always follow the instructions given by your doctor.

      You can take co-trimoxazole either with or without food, but if you find it upsets your stomach it may help to take it with some food.

      Try to take the medicine at regular intervals. If you forget to take a dose take it as soon as you remember, unless it's nearly time for your next dose. In this case just leave out the missed dose and take your next dose as normal. Don't take a double dose to make up for a missed dose.

      Unless your doctor tells you otherwise, it's important that you finish the prescribed course of this antibiotic medicine, even if you think you don't need it any more.

      Can I drink alcohol with Septrin?

      There is no 'do not drink alcohol' warning that applies to taking co-trimoxazole because it doesn't specifically affect the medicine itself.

      However, just be aware that if you feel unwell with an infection or find co-trimoxazole gives you a headache or upset stomach or makes you feel dizzy then this might be made worse by drinking alcohol. It's also possible that drinking excessive amounts of alcohol with co-trimoxazole could increase the risk of getting side effects on your liver.

      What are the side effects of Septrin?

      Medicines and their possible side effects can affect people in different ways. The following are some of the side effects that may be associated with co-trimoxazole. Just because a side effect is stated here doesn't mean that all people taking this antibiotic will experience that or any side effect.

      Very common side effects (affect more than 1 in 10 people)

      • Increased amount of potassium in the blood (hyperkalaemia).

        Common side effects (affect between 1 in 10 and 1 in 100 people)

        • Headache.
        • Diarrhoea.
        • Feeling sick.
        • Rash. See your doctor if you get a rash.
        • Overgrowth of the yeast Candida, which may cause infection such as thrush. Get advice from your pharmacist if you think you have developed a new infection while taking this antibiotic.
          How to cope with common side effects of medicines

          Very rare side effects (affect fewer than 1 in 10,000 people)

          • Problems with your blood cells. Tell your doctor if you experience unexplained bruising or bleeding, purple spots, sore throat, mouth ulcers, fever or feeling tired or generally unwell. If you're taking co-trimoxazole for long periods of time your doctor may want you to have regular blood tests to check your blood cells.
          • Inflammation of the bowel (colitis). Tell your doctor if you get diarrhoea that is severe, persistent or contains blood or mucus.
          • Liver problems. Tell your doctor if you experience yellow skin or eyes (jaundice).
          • Skin reactions, such as severe rashes, hives, blistering, peeling, itching and increased sensitivity to sunlight. See your doctor straight away if you get any of these.
          • Inflammation of the pancreas (pancreatitis).
          • Kidney problems.

            Read the leaflet that comes with the medicine or talk to your doctor, nurse or pharmacist if you want any more information about the possible side effects of Septrin. If you think you have experienced a side effect, did you know you can report this using the yellow card website?

            Can I take other medicines with Septrin?

            Before you take Septrin, tell your doctor or pharmacist if you're already taking any medicines, including those bought without a prescription and herbal medicines. Similarly, always check with your doctor or pharmacist before taking any new medicines while you're taking Septrin.

            Some key points are:


            If you need to take a painkiller while you're taking co-trimoxazole it's fine to take paracetamol. You should check with your doctor or pharmacist before taking ibuprofen.


            Co-trimoxazole doesn't affect hormonal contraceptives such as the pill. However, if you experience vomiting or diarrhoea while taking this antibiotic, this can potentially make your pill less effective at preventing pregnancy. If this happens to you, follow the instructions for vomiting and diarrhoea described in the leaflet provided with your pills.


            Co-trimoxazole may enhance the blood sugar lowering effect of repaglinide and sulphonylureas such as glibenclamide, gliclazide and tolbutamide that are used to treat type 2 diabetes. This is uncommon but may cause hypoglycaemia in a few people taking this combination of medicines.


            Co-trimoxazole may enhance the anti-blood-clotting effect of anticoagulants such as warfarin, which may increase the risk of bleeding. If you're taking warfarin your doctor may want to check your blood clotting time (INR) after you start and finish treatment with co-trimoxazole.

            is it safe to take different medicines together?

            Other medicines

            You might need some extra monitoring if you're taking any of the following medicines with co-trimoxazole - ask your pharmacist for more information:

            • an ACE inhibitor medicine, eg ramipril
            • aliskiren
            • an angiotensin blocker, eg losartan
            • ciclosporin
            • dapsone
            • digoxin
            • drospirenone
            • lamivudine
            • methotrexate
            • phenytoin
            • potassium salts, eg potassium citrate for cystitis
            • a potassium-sparing diuretic, eg spironolactone, eplerenone
            • potassium supplements
            • prilocaine
            • procainamide
            • pyrimethamine
            • a thiazide diuretic, eg bendroflumethiazide, hydrochlorothiazide
            • rifampicin
            • zidovudine.


              Oral typhoid vaccine (Vivotif) should not be taken until at least three days after you have finished a course of this antibiotic, because the antibiotic could make the vaccine less effective.

              Last updated

              Advertisement - Continue Reading Below

              Top Articles
              Latest Posts
              Article information

              Author: Merrill Bechtelar CPA

              Last Updated: 05/04/2023

              Views: 6520

              Rating: 5 / 5 (50 voted)

              Reviews: 89% of readers found this page helpful

              Author information

              Name: Merrill Bechtelar CPA

              Birthday: 1996-05-19

              Address: Apt. 114 873 White Lodge, Libbyfurt, CA 93006

              Phone: +5983010455207

              Job: Legacy Representative

              Hobby: Blacksmithing, Urban exploration, Sudoku, Slacklining, Creative writing, Community, Letterboxing

              Introduction: My name is Merrill Bechtelar CPA, I am a clean, agreeable, glorious, magnificent, witty, enchanting, comfortable person who loves writing and wants to share my knowledge and understanding with you.