PREGNANCY AND BREASTFEEDING SAFETY: 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.
STORAGE: The tablets should be kept at room temperature, 15 C -30 C (59 F - 86 F).
DOSAGE: 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.
DRUG CLASS AND MECHANISM: Bactrim 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.
Medically reviewed by Eni Williams, PharmD, PhD
Reference: FDA Prescribing Information
Quick GuideHIV AIDS Pictures Slideshow: Myths and Facts on Symptoms and Treatments
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
Need help identifying pills and medications?
Use the pill identifier tool on RxList.