You should not use this medication if you are allergic to sulfamethoxazole or trimethoprim, if you are pregnant or breast-feeding, or if you have anemia (lack of red blood cells) caused by folic acid deficiency.
Before using sulfamethoxazole and trimethoprim, tell your doctor if you have kidney or liver disease, a folic acid deficiency, asthma or severe allergies, AIDS, a glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), or if you are malnourished.
Take this medication for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Sulfamethoxazole and trimethoprim will not treat a viral infection such as the common cold or flu.
Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or has blood in it, call your doctor. Do not use any medicine to stop the diarrhea unless your doctor has told you to.
Avoid exposure to sunlight, sunlamps, or tanning beds. This medication can make your skin more sensitive to sunlight, and a sunburn may result. Wear protective clothing and use sunscreen (SPF 15 or higher) when you are outdoors.