- Side Effects
- Drug Interactions
- Pregnancy & Breastfeeding
- What Else to Know
Brand Names: Bactrim, Bactrim DS, Sulfatrim Pediatric
Drug Class: Antibiotics, Combos, Sulfonamides
What are sulfamethoxazole and trimethoprim, and what are they used for?
Sulfamethoxazole/trimethoprim is used for treating infections due to susceptible bacteria. Examples include urinary tract infections, flares of chromic bronchitis due to bacteria, middle ear infections, for prevention of infections due to pneumococcus in organ transplant recipients, for the treatment or prevention of Pneumocystis carinii pneumonia, chancroid, and prevention of toxoplasma encephalitis in patients with AIDS.
Sulfamethoxazole and trimethoprim is a combination of two synthetic (man-made) antibiotics, sulfamethoxazole, and trimethoprim. Both drugs reduce the ability of some bacteria to utilize folic acid for growing.
- Sulfamethoxazole is an anti-bacterial sulfonamide, a "sulfa" drug. It disrupts the production of dihydrofolic acid while trimethoprim disrupts the production of tetrahydrofolic acid. Dihydrofolic acid and tetrahydrofolic acid are forms of folic acid that bacteria and human cells use for producing proteins.
- Trimethoprim inhibits production of tetrahydrofolic acid by inhibiting the enzyme responsible for making tetrahydrofolic acid from dihydrofolic acid.
By combining both drugs, two important steps required in the production of bacterial proteins are interrupted, and the combination is more effective than either drug alone. Bactrim was approved by the FDA in 1973.
What are the side effects of sulfamethoxazole and trimethoprim?
Common side effects of sulfamethoxazole/trimethoprim are:
Other side effects include:
What is the dosage for sulfamethoxazole and trimethoprim?
- The recommended adult dose for urinary tract infections is one double strength tablet (Bactrim DS, Septra DS) or two single strength tablets every 12 hours for 10 to 14 days.
- Flares of chronic bronchitis are treated with a similar regimen for 14 days.
- Sulfamethoxazole/trimethoprim should be taken with 6 to 8 ounces of liquid to prevent crystals from forming in the urine. Persons with advanced kidney disease may require lower doses.
Which drugs interact with sulfamethoxazole and trimethoprim?
Sulfamethoxazole/trimethoprim can enhance the blood-thinning effects of warfarin, possibly leading to bleeding. Sulfonamides such as sulfamethoxazole can increase the metabolism (break-down and elimination) of cyclosporine (causing loss of effectiveness of cyclosporine), and can add to the kidney damage caused by cyclosporine.
Blood levels of phenytoin (Dilantin) may be increased by treatment with sulfamethoxazole/trimethoprim. This may lead to side effects associated with phenytoin (Dilantin, Dilantin-125) such as dizziness, and reduced attention.
Sulfamethoxazole/trimethoprim also may increase blood levels of digoxin (Lanoxin) and possibly lead to serious toxic effects. Anemia, due to a reduction in folic acid, can occur in persons receiving sulfamethoxazole/trimethoprim in combination with:
- valproic acid (Depakote, Depakote ER, Depakene, Depacon, Stavzor),
- methotrexate (Rheumatrex, Trexall),
- triamterene, or
Increased blood levels of potassium may occur when sulfamethoxazole/trimethoprim is combined with ACE inhibitors.
Pregnancy and breastfeeding
- Use of sulfonamides may cause bilirubin to be displaced from proteins in the infant's blood. Displacement of bilirubin can lead to jaundice and a dangerous condition called kernicterus in the infant. For this reason, sulfamethoxazole/trimethoprim should not be used near-term (late in pregnancy) among women.
- Sulfamethoxazole/trimethoprim should not be used by nursing mothers because sulfamethoxazole is excreted in milk and can cause kernicterus.
What else should I know about sulfamethoxazole and trimethoprim?
What preparations of sulfamethoxazole and trimethoprim are available?
- Tablets: 160 mg trimethoprim and 800 mg sulfamethoxazole (Bactrim DS, Septra DS); 80 mg trimethoprim and 400 mg sulfamethoxazole (Bactrim; Septra).
How should I keep sulfamethoxazole and trimethoprim stored?
- The tablets should be kept at room temperature, 15 C -30 C (59 F - 86 F).
Sulfamethoxazole and trimethoprim is a drug combination prescribed for urinary tract infections (UTIs), middle ear infections, respiratory infections, pneumonia, chancroid, for the prevention of infections of transplant recipients, and prevention of toxoplasma encephalitis in patients with AIDS. Common side effects of sulfamethoxazole/trimethoprim are dizziness, headache, lethargy, diarrhea, anorexia, nausea, vomiting, and rash.
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Treatment & Diagnosis
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