Trimethoprim is an antibiotic and is available as a single medication or in combination with sulfamethoxazole (a sulfonamide antibiotic).
Trimethoprim and the combination of trimethoprim and sulfamethoxazole (TMP/SMX) are effective against many gram-positive bacteria and gram-negative bacteria, including susceptible bacteria that are resistant to other antibiotics, such as methicillin-resistant Staphylococcus aureus (MRSA) and some protozoa (Cyclospora and Cystoisospora) and fungi (Pneumocystis). Using trimethoprim and sulfamethoxazole together enhances the effectiveness of both antibiotics.
These antibiotics work by preventing the bacteria from producing the type of folic acid they need to function.
Trimethoprim and Sulfamethoxazole
Medication | Common Uses | Some Potential Side Effects |
|---|---|---|
Trimethoprim* Trimethoprim/sulfamethoxazole (TMP/SMX) | Infections caused by susceptible bacteria that are resistant to other antibiotics, including methicillin-resistant Staphylococcus aureus (MRSA) Chronic infection of the prostate (prostatitis) Bladder infections in women Prevention of recurring urinary tract infections (UTIs) in women and children Intestinal infections due to various bacteria, such as Escherichia coli (E. coli) Treatment and prevention of pneumonia due to Pneumocystis jirovecii (a fungus) Trimethoprim alone: Chronic prostatitis and prevention and treatment of urinary tract infections in people who are allergic to sulfonamides | Nausea, vomiting, and diarrhea Allergic reactions (including rashes) Crystals in urine (rare) A decrease in white blood cell and platelet counts Sensitivity to sunlight Possibly increased tendency to bleed if used with warfarin Kidney failure in people who have kidneys that are not functioning well |
* Trimethoprim has side effects similar to those of sulfamethoxazole, but they are less common. | ||
(See also Overview of Antibiotics.)
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Trimethoprim/sulfamethoxazole should be avoided during the first trimester of pregnancy. Defects of the brain and spinal cord (neural tube defects), such as spina bifida, are a risk. The combination of trimethoprim/sulfamethoxazole should not be used during pregnancy or in newborns because it may cause jaundice and increases the risk of brain damage (kernicterus) in the fetus or in the newborn. (See also Safety of Medications During Pregnancy.)
Use of trimethoprim/sulfamethoxazole during breastfeeding is usually discouraged because sulfamethoxazole passes into breast milk. Use of trimethoprim during breastfeeding is generally considered acceptable. (See also Medication and Substance Use During Breastfeeding.)
