Trimethoprim-sulfamethoxazole (TMP-SMX), also known as co-trimoxazole, is a combination of two antimicrobial agents that act synergistically against a wide variety of bacteria. It is commonly used to treat urinary tract infections, middle ear infections, bronchitis, traveler’s diarrhea, and shigellosis (bacillary dysentery). TMP-SMX is also used to prevent or treat Pneumocystis jiroveci pneumonia or Pneumocystis carinii pneumonia. The two components, TMP and SMX, work sequentially to inhibit enzyme systems involved in the bacterial synthesis of tetrahydrofolic acid (THF). TMP binds to bacterial dihydrofolate reductase (in preference to human dihydrofolate reductase), preventing the formation of THF. SMX is a structural analog of para-aminobenzoic acid (PABA) and competes with PABA to inhibit the synthesis of dihydrofolic acid, an intermediate step in the formation of THF.
TMP-SMX is an important drug in the treatment of various bacterial infections. However, it is important to note that antibiotics should only be used when necessary and as prescribed by a healthcare professional. Overuse of antibiotics can lead to antibiotic resistance, which can make it difficult to treat bacterial infections. Therefore, it is important to use antibiotics judiciously and only when necessary.