Trimethoprim is an antibiotic used to treat bacterial infections. It works by stopping the growth of bacteria.

This antibiotic treats only bacterial infections. It will not work for viral infections (e.g., common cold, flu). Unnecessary use or overuse of any antibiotic can lead to its decreased effectiveness.

OTHER USES: This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

This drug may also be used to treat some lung infections (pneumocystis carinii pneumonia) and to prevent kidney infections in certain patients.

Take this medication by mouth on an empty stomach at least 1 hour before or 2 hours after a meal as directed by your doctor. It may be taken with food if stomach upset occurs. Dosage is based on your medical condition and response to therapy.

Antibiotics work best when the amount of medicine in your body is kept at a constant level. Therefore, take this drug at evenly spaced intervals.

Continue to take this medication until the full prescribed amount is finished, even if symptoms disappear after a few days. Stopping the medication too early may allow bacteria to continue to grow, which may result in a relapse of the infection.

Inform your doctor if your condition persists or worsens after several days.

Diarrhea, nausea, vomiting, stomach upset, loss of appetite, changes in taste, or headache may occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these rare but very serious side effects occur: swollen tongue, signs of infection (e.g., fever, persistent sore throat), easy bruising/bleeding, unusual paleness, mental/mood changes, tiredness with fast/pounding/irregular heartbeat, dark urine, persistent nausea/vomiting, stomach/abdominal pain, yellowing eyes/skin, stiff neck, persistent headache, muscle weakness.

This medication may rarely cause a severe intestinal condition (Clostridium difficile-associated diarrhea) due to a type of resistant bacteria. This condition may occur during treatment or weeks to months after treatment has stopped. Do not use anti-diarrhea products or narcotic pain medications if you have any of the following symptoms because these products may make them worse. Tell your doctor immediately if you develop: persistent diarrhea, abdominal or stomach pain/cramping, blood/mucus in your stool.

Use of this medication for prolonged or repeated periods may result in oral thrush or a new vaginal yeast infection (oral or vaginal fungal infection). Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms.

A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking trimethoprim, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

This medication should not be used if you have a certain medical condition. Before using this medicine, consult your doctor or pharmacist if you have: a certain type of anemia (due to folate deficiency).

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney disease, liver disease, vitamin deficiency (folate or folic acid), diabetes, blood disorders (e.g., bone marrow suppression, G6PD deficiency).

This medication may make you more sensitive to the sun. Avoid prolonged sun exposure, tanning booths, and sunlamps. Use a sunscreen and wear protective clothing when outdoors.

Kidney function declines as you grow older. This medication is removed by the kidneys. Therefore, elderly people may be at greater risk for mineral imbalance (high potassium blood level) and allergic reactions while using this drug.

This medication should be used only when clearly needed during pregnancy. Discuss the risks and benefits with your doctor.

Trimethoprim passes into breast milk. While there have been no reports of harm to nursing infants, consult your doctor before breast-feeding.

Your healthcare professionals (e.g., doctor or pharmacist) may already be aware of any possible drug interactions and may be monitoring you for it. Do not start, stop or change the dosage of any medicine before checking with them first.

This drug should not be used with the following medication because a very serious interaction may occur: dofetilide.

If you are currently using this medication listed above, tell your doctor or pharmacist before starting trimethoprim.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: digoxin, methotrexate, phenytoin, procainamide.

Although most antibiotics probably do not affect hormonal birth control such as pills, patch, or ring, some antibiotics may decrease their effectiveness. This could cause pregnancy. Examples include rifamycins such as rifampin or rifabutin. Be sure to ask your doctor or pharmacist if you should use additional reliable birth control methods while using this antibiotic.

This medication may interfere with certain laboratory tests (including kidney function and methotrexate blood levels), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

If overdose is suspected, contact a poison control center or emergency room immediately. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include nausea, vomiting, headache, dizziness, mental/mood changes, confusion.

Do not share this medication with others.

This medication has been prescribed for your current condition only. Do not use it later for another infection unless told to do so by your doctor. A different medication may be necessary in those cases.

Laboratory and/or medical tests (e.g., complete blood counts, kidney function, cultures) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

Store at room temperature between 59-77 degrees F (15-25 degrees C) away from moisture and light. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

Information last revised March 2013. Copyright(c) 2013 First Databank, Inc.