Sulfamethoxazole/Trimethoprim (Bactrim, Septra, and others) - Uses, Side Effects, and More

Who should not use sulfamethoxazole/trimethoprim?

Allergies to Ingredients. People who are allergic to any of the following should not take sulfamethoxazole/trimethoprim.

• Sulfamethoxazole/trimethoprim
• Bactrim or Bactrim DS
• Septra or Septra DS
• Sulfatrim
• Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific sulfamethoxazole/trimethoprim products they stock.

Low Platelets with Previous Sulfamethoxazole/Trimethoprim Use. Sulfamethoxazole/trimethoprim should not be used if you had low platelets while taking it in the past. Tell your health care provider if you have previously had low platelets while taking sulfamethoxazole/trimethoprim.

Children Less Than 2 Months Old. Sulfamethoxazole/trimethoprim should not be used in children under 2 months of age. Contact your health care provider before giving this medicine to your child if they are less than 2 months of age.

Anemia Due to Low Levels of Vitamin B9. Sulfamethoxazole/trimethoprim should not be used if you have anemia, or low red blood cells, due to low levels of vitamin B9 (also known as folate). If there is concern about you having this condition, your health care provider may do tests to see if you can safely take this medicine.

Liver Problems. Sulfamethoxazole/trimethoprim should not be used if your liver is not working as well as it should be. If there is a concern about the health of your liver, your health care provider may do tests to see if it is working well enough to take this medicine.

Kidney Problems. Sulfamethoxazole/trimethoprim should not be used if your kidneys are not working as well as they should be. If there is a concern about the health of your kidneys, your health care provider may do tests to see if they are working well enough to take this medicine.

Drug Interactions. Sulfamethoxazole/trimethoprim should not be taken while you are using certain other medicines. Before taking sulfamethoxazole/trimethoprim, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.  See the Interactions section for more details.

What should I know about sulfamethoxazole/trimethoprim before using it?

Do not take sulfamethoxazole/trimethoprim unless it has been prescribed to you by a health care provider. Take it as prescribed. 

Do not share sulfamethoxazole/trimethoprim with other people, even if they have the same condition as you. It may harm them.

Keep sulfamethoxazole/trimethoprim out of the reach of children.

Sulfamethoxazole/trimethoprim can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how sulfamethoxazole/trimethoprim affects you.

Sulfamethoxazole/trimethoprim can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

You should drink plenty of fluids while taking sulfamethoxazole/trimethoprim.

People who are 65 and older can be at greater risk for some side effects from sulfamethoxazole/trimethoprim. Talk to your health care provider about your risks if you are in this age group.

If you are taking sulfamethoxazole/trimethoprim oral liquid, shake the bottle well before each use and use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

What should I tell my health care provider before using sulfamethoxazole/trimethoprim?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if sulfamethoxazole/trimethoprim is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

• Asthma
• Kidney or liver problems
• Poor appetite
• Alcohol use disorder
• Low platelets
• Diabetes
• History of low levels of vitamin B-9 (folate)
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency
• Thyroid problems
• Porphyria, which is a condition where the body has problems making protein in red blood cells
• HIV or AIDS
• Phenylketonuria
• An allergy to sulfonamides

Pregnancy. Sulfamethoxazole/trimethoprim may cause harm to a fetus. Tell your health care provider if you are or plan to become pregnant. Your health care provider will let you know if you should take sulfamethoxazole/trimethoprim while you are pregnant or trying to get pregnant.

Breastfeeding. Sulfamethoxazole/trimethoprim passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take sulfamethoxazole/trimethoprim while breastfeeding.