Generic Name: Trimethoprim (trye-METH-oh-prim)Brand Name: Proloprim

Trimethoprim is used for:

Treating infections caused by certain bacteria.

Trimethoprim is an antibiotic. It works by killing sensitive bacteria.

Do NOT use Trimethoprim if:

  • you are allergic to any ingredient in Trimethoprim or to similar medicines
  • you are taking dofetilide
  • you have anemia caused by low levels of folate in the blood

Contact your doctor or health care provider right away if any of these apply to you.

Before using Trimethoprim :

Some medical conditions may interact with Trimethoprim . Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

  • if you are pregnant, planning to become pregnant, or are breast-feeding
  • if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
  • if you have allergies to medicines, foods, or other substances
  • if you have liver or kidney problems or blood problems (eg, anemia, porphyria)
  • if you have or are at risk for low levels of folate in the blood (eg, you have alcoholism, are elderly, you do not absorb nutrients from food properly, you are in a poor nutritional state, you are taking medicine for seizures)

Some MEDICINES MAY INTERACT with Trimethoprim . Tell your health care provider if you are taking any other medicines, especially any of the following:

  • Dofetilide because risk of severe heart problems may be increased by Trimethoprim
  • Methotrexate, phenytoin, or sulfones (eg, dapsone) because their actions and the risk of their side effects may be increased by Trimethoprim
  • Cyclosporine because its effectiveness may be decreased and risk of liver side effects may be increased by Trimethoprim

This may not be a complete list of all interactions that may occur. Ask your health care provider if Trimethoprim may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

How to use Trimethoprim :

Use Trimethoprim as directed by your doctor. Check the label on the medicine for exact dosing instructions.

  • Take Trimethoprim by mouth with or without food.
  • Trimethoprim works best if it is taken at the same time each day.
  • To clear up your infection completely, use Trimethoprim for the full course of treatment. Keep using it even if you feel better in a few days.
  • If you miss a dose of Trimethoprim , take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.

Ask your health care provider any questions you may have about how to use Trimethoprim .

Important safety information:

  • Trimethoprim may cause you to become sunburned more easily. Avoid the sun, sunlamps, or tanning booths until you know how you react to Trimethoprim . Use a sunscreen or wear protective clothing if you must be outside for more than a short time.
  • Contact your doctor right away if stomach pain or cramps, severe diarrhea, or bloody stools occur. Do not treat diarrhea without first checking with your doctor.
  • Be sure to use Trimethoprim for the full course of treatment. If you do not, the medicine may not clear up your infection completely. The bacteria could also become less sensitive to this or other medicines. This could make the infection harder to treat in the future.
  • Trimethoprim only works against bacteria; it does not treat viral infections (eg, the common cold).
  • Long-term or repeated use of Trimethoprim may cause a second infection. Tell your doctor if signs of a second infection occur. Your medicine may need to be changed to treat this.
  • Trimethoprim may interfere with certain lab tests. Be sure your doctor and lab personnel know you are using Trimethoprim .
  • Lab tests, including complete blood cell counts, may be performed while you use Trimethoprim . These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
  • Use Trimethoprim with caution in ELDERLY; they may be more sensitive to the effects of Trimethoprim .
  • Trimethoprim should be used with extreme caution in CHILDREN younger than 12 years old; safety and effectiveness in these children have not been confirmed.
  • Use Trimethoprim with extreme caution in CHILDREN younger than 10 years old who have diarrhea or an infection of the stomach or bowel.
  • PREGNANCY and BREAST-FEEDING: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Trimethoprim while you are pregnant. Trimethoprim is found in breast milk. If you are or will be breast-feeding while you use Trimethoprim , check with your doctor. Discuss any possible risks to your baby.

Possible side effects of Trimethoprim :

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Nausea; skin sensitivity to sunlight; stomach upset; vomiting.

Seek medical attention right away if any of these SEVERE side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); blistered, peeling, red, or swollen skin; bloody or black, tarry stools; chest pain; chills, fever, or sore throat; decreased urination; joint or muscle pain; irregular heartbeat; painful or stiff neck; purple patches under the skin; seizures; severe diarrhea; shortness of breath; stomach cramps/pain; unusual bruising or bleeding; unusual tiredness or weakness; unusually pale skin; vaginal irritation or discharge; yellowing of the skin or eyes.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. You may also report side effects at

If OVERDOSE is suspected:

Contact 1-800-222-1222 (the American Association of Poison Control Centers), your local poison control center (, or emergency room immediately. Symptoms may include confusion; depression; dizziness; drowsiness; fever, chills, or sore throat; loss of consciousness; severe nausea or vomiting; severe or prolonged headache; unusual bruising or bleeding.

Proper storage of Trimethoprim :

Store Trimethoprim at room temperature, between 59 and 77 degrees F (15 and 25 degrees C). Store away from heat, moisture, and light. Keep in a tight, light-resistant container. Do not store in the bathroom. Keep Trimethoprim out of the reach of children and away from pets.

General information:

  • If you have any questions about Trimethoprim , please talk with your doctor, pharmacist, or other health care provider.
  • Trimethoprim is to be used only by the patient for whom it is prescribed. Do not share it with other people.
  • If your symptoms do not improve or if they become worse, check with your doctor.

This information is a summary only. It does not contain all information about Trimethoprim . If you have questions about the medicine you are taking or would like more information, check with your doctor, pharmacist, or other health care provider.

  • Trimethoprim Prescribing Information (FDA)
  • Trimethoprim Detailed Consumer Information (PDR)
  • trimethoprim Advanced Consumer (Micromedex) - Includes Dosage Information
  • trimethoprim Concise Consumer Information (Cerner Multum)
  • Proloprim Prescribing Information (FDA)