Sulfamethoxazole With Trimethoprim (Bactrim®, Septra®)


Sulfamethoxazole with trimethoprim is also sometimes referred to as SMZ/TMP.


Sulfamethoxazole with trimethoprim (Bactrim®, Septra®) is a combination antibiotic used to treat infections in children who have had liver transplants. It is also used to prevent and treat Pneumocystis carinii pneumonia.

Types Available

Sulfamethoxazole with trimethoprim is taken orally or given by injection, The oral form is available as single-strength (80/400-mg) or double-strength (160/800-mg) tablets, or as a liquid.

How to Take

This medication can be taken with or without food. Your child's doctor will usually recommend taking this medication with a glass of water. Your child should also drink several additional glasses of water daily, unless otherwise directed.

Missed Doses

If your child misses a dose, it should be taken as soon as you or your child remembers. If it is within two hours of the time for the next dose, however, skip the missed dose and resume your child's usual dosing schedule. Do not double the dose to catch up.

Side Effects

If your child has an upset stomach when taking this medication, it may be helpful to give food or milk with each dose.

Limit your child's exposure to the sun while he or she is taking this medication. Sulfamethoxazole with trimethoprim can also cause sensitivity to sunlight. If your child must be outside for a long period, he or she should wear protective clothing, such as a hat and sunglasses, and use a sunscreen with a sun protection factor (SPF) of at least 15. Make sure the sunscreen your child uses does not contain PABA oil. PABA can interfere with the action of sulfamethoxazole with trimethoprim.

You may notice that your child has less of an appetite than usual. Sometimes, people taking this medication experience headaches, nausea, or vomiting.

Tell your transplant doctor or transplant coordinator right away if your child develops any of these rare side effects:

  • skin rash
  • difficulty breathing
  • itching
  • hives
  • chills
  • fever
  • sore throat
  • aching of joints or muscles
  • easy bleeding or bruising
  • yellowing of the eyes or skin
  • peeling skin
  • tiredness

Drug Interactions

Tell your doctor or pharmacist about any prescription or over-the-counter medications that your child is taking, so you can be warned of interactions and prevent them.


Your child should not stop taking this medication unless advised to do so by a transplant surgeon or your coordinator. Notify your doctor if your child has an allergy to sulfa drugs.


Store at room temperature.


Most pharmacies stock sulfamethoxazole with trimethoprim.

Learn more about other Intestine Transplant Drugs.