Bactrim is a type of medication made by combining the antibiotics trimethoprim and sulfamethoxazole, according to Drugs.com. Bactrim treats a range of bacterial infections, including urinary tract infections, ear infections, shigellosis, bronchitis, pneumocystis-type pneumonia and traveler's diarrhea.
Bactrim works by stopping bacterial growth. PDRHealth warns that Bactrim should never be used by children less than 2 months old, as it poses a risk of serious side effects. It is also not recommended for treatment of infections not caused by bacteria, such as viral infections such as influenza or the common cold. Bactrim is available in tablet form in both regular and double-strength formulations.
According to Wikipedia, Bactrim is part of the World Health Organization's List of Essential Medicines because of its ability to fight a broad range bacterial infections. Despite its high efficacy, Bactrim also has a higher rate of allergic reaction than either sulfamethoxazole or trimethoprim alone, which has led some countries to restrict its use.