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Trimethoprim and Sulfamethoxazole

By

Brian J. Werth

, PharmD, University of Washington School of Pharmacy

Last full review/revision Jun 2022| Content last modified Jun 2022
CLICK HERE FOR THE PROFESSIONAL VERSION
Topic Resources

Trimethoprim and the combination of trimethoprim and sulfamethoxazole (TMP/SMX) are effective against many gram-positive bacteria Overview of Gram-Positive Bacteria Gram-positive bacteria are classified by the color they turn after a chemical called Gram stain is applied to them. Gram-positive bacteria stain blue when this stain is applied to them. Other... read more and gram-negative bacteria Overview of Gram-Negative Bacteria Bacteria are classified by how they appear under the microscope and by other features. Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining... read more , including susceptible bacteria that are resistant to other antibiotics, such as methicillin-resistant Staphylococcus aureus ( MRSA Methicillin-resistant Staphylococcus aureus (MRSA) Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up)... read more Methicillin-resistant <i > Staphylococcus aureus </i> (MRSA) ) and some protozoa ( Cyclospora Cyclosporiasis Cyclosporiasis is an infection of the small intestine caused by the parasite Cyclospora cayetanensis. The main symptoms are watery diarrhea with abdominal cramping and nausea. People... read more Cyclosporiasis and Cystoisospora Cystoisosporiasis Cystoisosporiasis is infection with the parasite Cystoisospora (Isospora) belli. The main symptoms are watery diarrhea with abdominal cramping and nausea. People can become infected with... read more Cystoisosporiasis ) and fungi ( Pneumocystis Causes ). Using trimethoprim and sulfamethoxazole together enhances the effectiveness of both antibiotics.

These drugs work by preventing the bacteria from producing the type of folic acid they need to function.

Table

Trimethoprim and Sulfamethoxazole

Drug

Common Uses

Some Potential Side Effects

Trimethoprim*

Trimethoprim/sulfamethoxazole (TMP/SMX)

Bladder infections in women

Treatment and prevention of pneumonia due to Pneumocystis jirovecii Causes (a fungus)

Nausea, vomiting, and diarrhea

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.

Use During Pregnancy and Breastfeeding

Trimethoprim/sulfamethoxazole should be avoided during the first trimester of pregnancy. Defects of the brain and spinal cord ( neural tube defects Neural Tube Defects and Spina Bifida Neural tube defects are a certain type of birth defect of the brain, spine, and/or spinal cord. Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death. The... read more ), such as spina bifida Neural Tube Defects and Spina Bifida Neural tube defects are a certain type of birth defect of the brain, spine, and/or spinal cord. Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death. The... read more , are a risk. Trimethoprim/sulfamethoxazole should not be used during pregnancy or in newborns because this drug combination may cause jaundice Jaundice in the Newborn Jaundice is a yellow color to the skin and/or eyes caused by an increase in bilirubin in the bloodstream. Bilirubin is a yellow substance formed when hemoglobin (the part of red blood cells... read more Jaundice in the Newborn and increases the risk of brain damage ( kernicterus Complications of jaundice Jaundice is a yellow color to the skin and/or eyes caused by an increase in bilirubin in the bloodstream. Bilirubin is a yellow substance formed when hemoglobin (the part of red blood cells... read more Complications of jaundice ) in the newborn. (See also Drug Use During Pregnancy Drug Use During Pregnancy More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more .)

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 Drug Use During Breastfeeding Drug Use During Breastfeeding When mothers who are breastfeeding have to take a drug, they wonder whether they should stop breastfeeding. The answer depends on the following: How much of the drug passes into the milk Whether... read more .)

Drugs Mentioned In This Article

Generic Name Select Brand Names
PRIMSOL
BACTRIM, SEPTRA
NOTE: This is the Consumer Version. DOCTORS: CLICK HERE FOR THE PROFESSIONAL VERSION
CLICK HERE FOR THE PROFESSIONAL VERSION
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