sulfamethoxazole and trimethoprim, Bactrim, Septra (cont.)

DOSING: 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 INTERACTIONS: Sulfamethoxazole/trimethoprim can enhance the blood-thinning effects of warfarin (Coumadin), 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.

All sulfonamides can crystallize in urine when the urine is acidic. Since methenamine (Hiprex, Urex, Mandelamine) causes acidic urine, it should not be used with sulfonamides.

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 divalproex, valproic acid (Depakote, Depakote ER, Depakene, Depacon, Stavzor), methotrexate (Rheumatrex, Trexall), pyrimethamine, triamterene, or trimetrexate. Increased blood levels of potassium may occur when sulfamethoxazole/trimethoprim is combined with ACE inhibitors.

PREGNANCY: 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.

Medically Reviewed by a Doctor on 1/21/2015


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