Trimethoprim: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing

Uses

What is trimethoprim used for?

Trimethoprim is commonly used to treat bladder infections.

Trimethoprim may not be appropriate for all bladder infections, depending on which germs are causing the infection. Bacteria in some locations may have developed resistance to trimethoprim, which will make it less effective.

Trimethoprim may also be used for other conditions as determined by your healthcare provider.

How does trimethoprim work (mechanism of action)?

Trimethoprim kills certain types of bacteria by blocking their ability to create proteins and other substances that they need to grow and reproduce.

How is trimethoprim supplied (dosage forms)?

Brands and other names

Primsol
Proloprim
Trimpex

Dosage forms and strengths

100 mg oral tablets

How should I store trimethoprim?

Trimethoprim should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from light.

Side Effects

What are the most common side effects of trimethoprim?

The most common side effects of trimethoprim are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

Rash
Itching

There may be other side effects of trimethoprim that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of trimethoprim?

While less common, the most serious side effects of trimethoprim are described below, along with what to do if they happen.

Severe Allergic Reactions. Trimethoprim may cause allergic reactions, which can be serious. Stop using trimethoprim and get help right away if you have any of the following symptoms of a serious allergic reaction.

Breathing problems or wheezing
Racing heart
Fever or general ill feeling
Swollen lymph nodes
Swelling of the face, lips, mouth, tongue, or throat
Trouble swallowing or throat tightness
Itching, skin rash, or pale red bumps on the skin called hives
Nausea or vomiting
Dizziness, feeling lightheaded, or fainting
Stomach cramps
Joint pain

Antibiotic-associated Diarrhea. An overgrowth of germs called Clostridioides difficile, or “C. diff,” can happen in your gut with many types of antibiotics, including trimethoprim. This can cause a condition known as antibiotic-associated diarrhea and can happen even up to 2 months after stopping the antibiotic. Call your healthcare provider right away if you have any of the following symptoms of this condition.

Watery diarrhea
Diarrhea that does not go away
Blood in your stool (poop)
Severe stomach cramps
Fever that starts after you start or finish the medicine

Blood Disorders. Trimethoprim can cause blood disorders, such as low platelet levels (thrombocytopenia), low white blood cell levels (leukopenia), and low levels of a type of white blood cell called neutrophils (neutropenia). Tell your healthcare provider right away if you have any of the following symptoms of blood disorders.

Fever, chills, or sweats
Sore throat, cough, or shortness of breath
Easy bruising or bleeding
Frequent infection
Unusual weakness or tiredness
Mouth or throat sores
Swollen lymph nodes

Warnings & Precautions

Who should not use trimethoprim?

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

Trimethoprim
Primsol
Proloprim
Trimpex
Any of the ingredients in the specific product dispensed

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

Anemia due to Low Levels of Vitamin B-9. Trimethoprim should not be used if you have anemia, or low red blood cells, due to low levels of vitamin B-9 (also known as folate). If there is concern about you having this condition, your healthcare provider may do tests to determine if you can safely take this medicine.

What should I know about trimethoprim before using it?

Do not take trimethoprim unless it has been prescribed to you by a healthcare provider. Take it as prescribed.

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

Keep trimethoprim out of the reach of children.

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.

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

What should I tell my healthcare provider before using trimethoprim?

Tell your healthcare 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 determine if trimethoprim is right for you.

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

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

Kidney or liver problems
History of low levels of vitamin B-9 (folate)

Other Medicines and Supplements. Trimethoprim may interact with other medicines and supplements. Before using trimethoprim, tell your healthcare 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.

Pregnancy. Trimethoprim may cause harm to an unborn baby. Tell your healthcare provider if you are or plan to become pregnant. Your healthcare provider will advise you if you should take trimethoprim while you are pregnant or trying to get pregnant.

Breastfeeding. Trimethoprim passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should take trimethoprim while breastfeeding.

Interactions

Does trimethoprim interact with foods or drinks?

There are no known interactions between trimethoprim and foods or drinks.

There are no known interactions between trimethoprim and alcohol, but heavy drinking can slow your immune response and make it harder for your body to fight infection.

Does trimethoprim interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. In particular, make sure that you discuss if you are using phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures, before taking trimethoprim.

This may not be a complete list of medicines that can interact with trimethoprim. Always check with your healthcare provider.

Does Trimethoprim interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much trimethoprim?

If you or someone else has used too much trimethoprim, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of trimethoprim?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.

It is important to complete your prescribed course of trimethoprim, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to trimethoprim or other similar medicines.