You should not use  sulfamethoxazole and trimethoprim if you have severe liver disease, kidney disease that is not being monitored, anemia caused by folic acid deficiency, if you take dofetilide, or if you have had low platelets caused by using trimethoprim or a sulfa drug.
You should not take sulfamethoxazole and trimethoprim if you are pregnant or breastfeeding.
Before taking this medicine
You should not use this medicine if you are allergic to sulfamethoxazole or trimethoprim, or if you have:
severe liver disease;
kidney disease that is not being treated or monitored;
anemia (low red blood cells) caused by folic acid deficiency;
a history of low blood platelets after taking trimethoprim or any sulfa drug; or
if you take dofetilide.
Sulfamethoxazole and trimethoprim may harm an unborn baby or cause birth defects. Tell your doctor if you are pregnancy or if you become pregnant.
Do not breastfeed while using this medicine.
This medicine should not be given to a child younger than 2 months old.
Tell your doctor if you have ever had:
kidney or liver disease;
a folate (folic acid) deficiency;
asthma or severe allergies;
a thyroid disorder;
malnourishment;
alcoholism;
high levels of potassium in your blood;
porphyria, or glucose-6-phosphate dehydrogenase (G6PD) deficiency; or
if you use a blood thinner (such as warfarin) and you have routine "INR" or prothrombin time tests.
