Bactrim and Bactrim DS are antibiotics used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, shigellosis, and Pneumocystis jiroveci pneumonia. Bactrim and Bactrim DS contain a combination of two antibiotics, sulfamethoxazole and trimethoprim, that treat different types of infection caused by bacteria. Bactrim DS (double strength) tablets are twice as strong as Bactrim tablets. 

Sulfamethoxazole is a sulfonamide antibiotic that prevents the growth of susceptible bacteria by interfering with their ability to make folic acid. Trimethoprim is an antifolate antibiotic that works by inhibiting an enzyme, resulting in bacteria's inability to make DNA and survive. Sulfamethoxazole and trimethoprim are combined because they are complementary and have a greater effect when used together. 

To help reduce the development of drug-resistant bacteria and maintain sulfamethoxazole-trimethoprim effectiveness, this medicine should be used only to treat infections proven or strongly suspected to be caused by susceptible bacteria.

Bactrim DS side effects

Common Bactrim side effects

Common Bactrim DS and Bactrim side effects are nausea, vomiting, loss of appetite, and skin rash.

Serious Bactrim side effects

Get emergency medical help if you have signs of an allergic reaction to this medicine (hives, cough, chest pain, shortness of breath, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include skin rash, fever, swollen glands, joint pain, muscle aches, severe weakness, pale skin, unusual bruising, or yellowing of your skin or eyes.

Call your doctor at once if you have:

• severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
• any skin rash, no matter how mild;
• yellowing of your skin or eyes;
• a seizure;
• new or unusual joint pain;
• increased or decreased urination;
• swelling, bruising, or irritation around the IV needle;
• increased thirst, dry mouth, fruity breath odor;
• new or worsening cough, fever, trouble breathing;
• high blood potassium - nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement;
• low blood sodium - headache, confusion, problems with thinking or memory, weakness, feeling unsteady; or
• low blood cell counts - fever, chills, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet, feeling light-headed or short of breath.