Bactrim DS Tablet is used to treat bacterial infections of the urinary tract, respiratory tract (bronchitis), ear (otitis media), lungs (pneumonia), skin, brain and toxoplasmosis (infection caused by a bacteria called toxoplasma). It contains Trimethoprim and Sulfamethoxazole, which stops the growth of bacteria and kills them. Thereby, it helps to treat bacterial infections. In some cases, you may experience certain common side effects, such as high levels of potassium in the blood, palpitations (abnormal heartbeats), thrush or candidiasis (fungal infection), headache, nausea, diarrhoea, and skin rashes. Before taking this medicine, you should tell your doctor if you are allergic to any of its components or if you are pregnant/breastfeeding, and about all the medications you are taking and pre-existing medical conditions.