Known brand names include Bactrim and Sulfatrim.
A combination antibiotic pill (a sulfa drug plus trimethoprim) for urinary tract infections, ear infections in children, bronchitis flares, traveler's diarrhea, shigellosis, and Pneumocystis pneumonia. Rash is common and severe skin reactions can occur; it can also raise potassium and strengthen warfarin.
Trimethoprim-sulfamethoxazole works because many bacteria must make their own folic acid to build DNA and proteins. Sulfamethoxazole blocks an early step by competing with a building block called PABA. Trimethoprim then blocks the next step by holding onto the enzyme that turns that folic acid into its working form. With two steps in a row blocked, the bacteria cannot make what they need to grow.
Both drugs are absorbed quickly, peak in the blood 1 to 4 hours after a dose, and can still be detected 24 hours later. The kidneys clear them, so they reach much higher levels in urine than in blood, and they also get into middle ear fluid and mucus from the airways. Using the two together slows how fast bacteria become resistant. People should start to feel better within the first few days.
Trimethoprim-sulfamethoxazole is an antibiotic pill that combines two drugs to treat infections caused by bacteria. It treats urinary tract infections, ear infections in children, and flares of long-term bronchitis in adults. It also treats shigellosis, a bacterial infection of the bowel, and traveler's diarrhea in adults. It does not work against viruses.
It also treats Pneumocystis pneumonia, a serious lung infection, and prevents it in people with weakened immune systems who are at higher risk. The tablets are taken by mouth, and the full course should be finished even after symptoms ease so the infection clears and bacteria do not become resistant. For a first, uncomplicated urinary tract infection, the label prefers a single antibiotic over this combination, and it should not be used for group A strep infections because it does not clear them. It is not given to babies younger than 2 months, and it is not used to prevent ear infections or for long courses to treat them.
Nausea, vomiting, loss of appetite, rash, and hives are the most common side effects. The label treats severe reactions as the main danger, including life-threatening skin reactions, liver failure, blood disorders, lung injury, and shock. It also warns about high potassium, low sodium, low blood sugar, C. difficile diarrhea, low platelets, possible birth defects, and harm to newborns.