Hematologist
CION Cancer Clinics
Cotrimoxazole to prevent PJP during blood cancer treatment | CION Cancer Clinics
Cotrimoxazole is prescribed to prevent PJP, a serious lung infection that can strike when blood cancer treatment or long steroid courses weaken your immune system. It protects you before trouble starts, so it is taken even when you feel well, and often for months after treatment ends. This page explains who is given it, which side effects need a same-day call, and what to ask your haematologist. At CION Cancer Clinics, our haematology team supports patients and families through treatment, cost questions and life at home.
BP
Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
The short answer
Why has my haematologist prescribed cotrimoxazole?
Cotrimoxazole is being used to stop a lung infection called PJP before it starts. You are not being treated for an infection you already have. The tablet is a shield, taken while your treatment keeps part of your immune system weak.
What PJP is
PJP stands for Pneumocystis jirovecii pneumonia. The germ behind it is a fungus that many healthy people carry without ever knowing. A strong immune system keeps it quiet. When certain blood cancer treatments or long steroid courses weaken the immune cells that normally hold it back, it can cause a serious chest infection. It starts slowly, with a dry cough, breathlessness and fever, and can become severe.
Why a tablet instead of waiting to see
PJP is much easier to stop than to treat. Once it has taken hold, it often needs a hospital stay, oxygen and strong medicines through a drip. Cotrimoxazole is an old, well-studied, low-cost medicine, and in people at risk it lowers the chance of PJP a great deal. That is why many haematology teams prescribe it as a routine part of treatment.
Cotrimoxazole is an antibiotic, but here it is used for protection, not to treat an illness you already have.Who it is for
Who is usually given it?
Your haematologist decides based on your diagnosis, your treatment and your blood tests. These are the most common situations.
Acute leukaemia treatment
Many treatment plans for acute lymphoblastic leukaemia include it from the start, because the treatment is long and leans heavily on steroids.
Long steroid courses
Steroids such as prednisolone or dexamethasone, taken for weeks rather than days, weaken the immune cells that keep PJP away.
Certain lymphoma and CLL medicines
Some medicines lower a type of white cell called the lymphocyte for a long time, even after the treatment ends.
Examples your team may mention
- Fludarabine and bendamustine
- Alemtuzumab
- Some combination plans with rituximab
After a stem cell transplant
People who have had a transplant at a transplant centre are usually kept on protection for months. The transplant team sets how long.
Not sure whether this applies to you?
Ask an oncologist
!
Two things that cannot wait
A new rash with blisters, peeling skin, sore eyes or mouth ulcers while on cotrimoxazole needs a doctor the same day. So does a fever with a low white count. Go to the nearest emergency department or call 108, show the medicine list, and say you are on blood cancer treatment. Do not wait to see if it settles.
Over the months
How does it fit into my treatment?
-
It is started with treatment
Your team usually starts it around the same time as chemotherapy or steroids. The prescription says which days to take it. Many schedules are not every day, so write the days on the family calendar.
-
Blood tests keep watch
Cotrimoxazole can lower blood counts and affect the kidneys and the potassium level. Your routine blood tests already look for this, so bring up any result you do not understand at the next visit.
-
It may be paused around some medicines
It can interact with methotrexate and a few other drugs. Your haematologist may hold it for a short while around those treatments. That decision belongs to the team, not the family.
-
It continues after treatment ends
The immune system recovers more slowly than the blood counts. Many people stay on it for a period after their last cycle, and that is expected.
-
Your team stops it
Only your haematologist can decide it is safe to stop, usually from your treatment history and sometimes a lymphocyte count.
Commonly believed
What do families often get wrong about it?
"He has no cough or fever, so he does not need it."
That is exactly the point. The tablet works by being in the body before the germ causes trouble. Feeling well is a sign that protection is working, not a sign it is no longer needed. Missed days leave a gap, so ask the team what to do if a tablet is missed.
"It is only an antibiotic, so any chemist tablet will do."
Most common antibiotics do nothing against PJP. Cotrimoxazole is chosen because it works against this particular germ. Do not swap it for a medicine a local shop suggests.
"She had a sulpha allergy years ago, but it was minor."
Cotrimoxazole contains a sulpha medicine. Any past reaction, however small it seemed, must be told to the haematologist before the first tablet. There are other options.
"Once chemotherapy is finished, the tablet can be stopped."
The immune system often stays weak for months after the last cycle. Stopping early is one of the most common ways people lose protection just when they relax.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Side effects
Which side effects can wait, and which cannot?
Mention at the next visit
Call the team the same day
Mild stomach upset or feeling sick after the tablet
Vomiting so that tablets cannot stay down
A small, flat rash that barely itches
A spreading rash, blisters, peeling or sore eyes
A blood test result flagged slightly low
Yellow eyes, dark urine or much less urine than usual
Loss of taste for food
Unusual bruising, bleeding or a fever
Being straight with you
What if cotrimoxazole does not suit me?
Cotrimoxazole is not right for everyone. People with a sulpha allergy, some kidney problems, a severe reaction to it before, or counts that stay too low may be moved to another medicine. People with G6PD deficiency, an inherited condition affecting red cells, need extra care with it and with some of the alternatives.
The other options
Your haematologist may choose dapsone, atovaquone, or pentamidine given as a mist you breathe in at set intervals. Each works, but none is quite as reliable or as low-cost as cotrimoxazole, and each has its own side effects. The choice depends on your kidneys, your blood tests and what else you take.
What this page cannot tell you
It cannot tell you whether you personally need protection, which days you should take it, or when it is safe to stop. Those depend on your diagnosis, your treatment plan and how your immune system recovers. It also cannot tell you whether a cough is PJP. A chest infection in someone on blood cancer treatment always needs to be seen.
Bring every medicine box, including ones from other doctors, to your haematology visit. Interactions are easier to catch when the team can see them all.Questions we are asked
Common questions about cotrimoxazole and PJP
I missed a tablet. What should I do?
Do not double up on your own. Missing one tablet is unlikely to cause harm straight away, but the right way to catch up depends on your schedule. Call your haematology team or the helpline and tell them which day was missed. Setting a phone alarm for tablet days helps a great deal.
Is cotrimoxazole the same as Septran or Bactrim?
Those are brand names that contain cotrimoxazole. Chemists may give a different brand from the one on your prescription, and the medicine inside should be the same. Check the strength printed on the strip against your prescription, and ask the chemist or your team if anything looks different.
Why am I taking an antibiotic when I have no infection?
Because it is protecting you, not treating you. Your treatment weakens the immune cells that normally keep the PJP germ quiet. The tablet fills that gap until your immune system recovers. Feeling well while taking it is exactly what the team hopes to see.
Can it lower my blood counts?
It can, usually mildly. Because your treatment also lowers counts, it can be hard to tell which one is responsible. Your haematologist reads your blood tests with both in mind and may change the plan if needed. Please do not stop the tablet on your own because of a low result.
Can I drink alcohol or take other medicines with it?
Alcohol is wise to avoid during blood cancer treatment in general. Several medicines interact with cotrimoxazole, including methotrexate, some blood thinners and some diabetes and blood pressure tablets. Tell every doctor who prescribes for you that you are on it, including your family doctor and dentist.
Is it safe for children with leukaemia?
It is widely used in children with leukaemia and is part of many standard plans. Children often take it as a syrup. The amount depends on weight and is set by the child's team. If your child refuses it or vomits it up, tell the team rather than quietly skipping days.
Do I need to drink more water?
Drinking enough fluid is sensible, because the medicine passes through the kidneys. It also helps with other treatment side effects. If you have heart or kidney problems and have been told to limit fluids, follow that advice instead and ask your team what is right for you.
Is it covered by Aarogyasri or insurance?
Cotrimoxazole is a low-cost medicine. When it is part of an approved haematology treatment plan it is usually covered with the rest of your care under Aarogyasri, CGHS, ECHS, EHS, PM-JAY or cashless insurance. Scheme rules change, so check your current cover with the helpline.
Your Haematologist
Meet CION's haematologist. One specialist for your blood report and your plan.
Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Patient stories
Hear it from people we have treated
Every story is a video, in the patient's own words. Nothing here is a written testimonial.
Sources
- NHS — Co-trimoxazole
- National Cancer Institute — Infection and cancer treatment
- Blood Cancer UK — Blood cancer information and support
- Macmillan Cancer Support — Cancer information and support
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Neutropenic fever: the emergency to knowWhat to do the moment a fever startsAntifungal protection in acute leukaemiaThe other preventive medicine often given alongsideVaccination during blood cancer treatmentWhich vaccines are safe and whenCounts, fever and infection in haematologyThe full guide to staying safe with low counts
Talk to us
Unsure why a medicine is on your list?
Call the helpline with your prescription in hand. The haematology team will explain what each medicine is for. One helpline serves every CION centre.