Cotrimoxazole (Sulfamethoxazole + Trimethoprim): Chemical Structure, Mechanism, Uses, Side effects

Chemical formula:

• C10H11N3O3S (sulfamethoxazole), C14H18N4O3 (trimethoprim)

Structure of Cotrimoxazole

Mechanism of action:

• Cotrimoxazole is a combination of two drugs that target different steps in the bacterial folate synthesis pathway. Sulfamethoxazole inhibits dihydropteroate synthase, preventing the formation of dihydrofolate, while trimethoprim inhibits DHFR, preventing the conversion of dihydrofolate to tetrahydrofolate. This synergistic effect leads to a more potent disruption of bacterial DNA synthesis and cell death.

Uses:

• Cotrimoxazole is used for the treatment of various bacterial infections, including urinary tract infections, respiratory infections (such as bronchitis and pneumonia), gastrointestinal infections (like shigellosis and traveler's diarrhea), and skin infections. It is also used for the prevention and treatment of Pneumocystis jiroveci pneumonia in immunocompromised patients.

Side effects:

• Common side effects of cotrimoxazole include gastrointestinal disturbances (nausea, vomiting, diarrhea), skin rash, and itching. Less common side effects include blood dyscrasias, such as leukopenia, thrombocytopenia, and megaloblastic anemia, as well as hyperkalemia and liver toxicity. In rare cases, it may cause serious skin reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis.