Overview
Co-trimoxazole to treat hidradenitis suppurativa or HS
This information is about taking a medicine called co-trimoxazole (Septrin®) to treat the skin condition hidradenitis suppurativa (HS).
Co-trimoxazole is a combination of 2 antibiotics called trimethoprim and sulphamethoxazole. This medicine is used to:
- treat infections
- reduce inflammation
- prevent flare-ups of HS
This information is intended to be read together with any patient information from the manufacturer. It covers:
- the use of an unlicensed medicine
- how to take the medicine
- what to do if you forget to take the medicine
- the possible side effects of the medicine
- other useful information about taking the medicine
If you have any questions or concerns, please speak to a doctor or nurse caring for you.
Taking an unlicensed medicine
Co-trimoxazole is not officially approved (licensed) for use in HS. However, it is commonly used for other types of skin infections.
Read our information about unlicensed medicines. You can also contact our medicines advice patient helpline.
How to take the medicine
You take co-trimoxazole by mouth in tablet or liquid form, usually 2 times a day. Your doctor tells you how long to take the medicine.
If you forget to take the medicine
If you forget a dose (prescribed amount) of the medicine, do not take a double dose. Tell your doctor or nurse and keep to your regular schedule.
Side effects of the medicine
Each person reacts differently to medicines. You will not necessarily get every side effect mentioned in this section.
Call 999 or go to A&E now if you have:
- an allergic reaction (difficulty with breathing, closing of the throat, or swelling of the lips, tongue or face)
- signs of infection, such as a new long-lasting cough or high temperature (fever)
- joint or muscle aches
- yellowing of the skin or eyes (jaundice)
- a skin rash
- unusual tiredness or weakness
- unusual bruising or bleeding
If you get any of these serious side effects, stop taking co-trimoxazole.
Other less serious side effects may be more likely.
Speak to the HS team if you:
- feel dizzy or lose your balance
- lose your appetite
- have an upset stomach
If you get any of these side effects, continue to take co-trimoxazole until the HS team gives you advice.
There are also other possible side effects. You can speak to a member of the HS team about any side effect that seems unusual or is especially bothersome.
Other information about taking co-trimoxazole
If you are advised to take co-trimoxazole for an extended time, you will need to have a blood test every month. This can be done in the hospital clinic or at your GP surgery.
The blood test is to check that your blood counts (which measure the number and size of the different cells in your blood) do not drop. This is a rare but serious side effect of taking co-trimoxazole.
You need to avoid taking co-trimoxazole if you have G6PD deficiency (an inherited condition resulting in lack of an enzyme that helps red blood cells to work correctly). You have a blood test to check for this condition.
Here are some important safety tips if you take co-trimoxazole:
Do
- tell the healthcare professional who prescribes co-trimoxazole about any other medicines that you take
- keep all medicines in a safe place where children cannot reach them
- return any leftover supplies of medicine to the pharmacist if your healthcare professional tells you to stop treatment with co-trimoxazole or the medicine passes its expiry date
Resource number: 5539/VER1
Last reviewed: August 2025
Next review due: August 2028
