A bacteriostatic antibacterial agent that interferes with folic acid synthesis in susceptible bacteria. Its broad spectrum of activity has been limited by the development of resistance. (From Martindale, The Extra Pharmacopoeia, 30th ed, p208)
For the treatment bacterial infections causing bronchitis, prostatitis and urinary tract infections.
Sulfamethoxazole is a sulfonamide drug that inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA) for binding to dihydropteroate synthetase (dihydrofolate synthetase). Sulfamethoxazole is bacteriostatic in nature. Inhibition of dihydrofolic acid synthesis decreases the synthesis of bacterial nucleotides and DNA. Sulfamethoxazole is normally given in combination with Trimethoprim, a dihydrofolate reductase inhibitor, which inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Studies have shown that bacterial resistance develops more slowly with the combination of the two drugs than with either Trimethoprim or Sulfamethoxazole alone.
Mechanism of action
Sulfonamides inhibit the enzymatic conversion of pteridine and p-aminobenzoic acid (PABA) to dihydropteroic acid by competing with PABA for binding to dihydrofolate synthetase, an intermediate of tetrahydrofolic acid (THF) synthesis. THF is required for the synthesis of purines and dTMP and inhibition of its synthesis inhibits bacterial growth. Pyrimethamine and trimethoprim inhibit dihydrofolate reductase, another step in THF synthesis, and therefore act synergistically with the sulfonamides.
Route of administration
Antibacterials for Systemic Use
Antiinfectives for Systemic Use
Blood Glucose Lowering Agents
Chemical Actions and Uses
Cytochrome P-450 CYP2C8 Inhibitors
Cytochrome P-450 CYP2C8 Inhibitors (moderate)
Cytochrome P-450 CYP2C9 Inhibitors
Cytochrome P-450 CYP2C9 Inhibitors (moderate)
Cytochrome P-450 CYP2C9 Substrates
Cytochrome P-450 CYP3A Inhibitors
Cytochrome P-450 CYP3A4 Substrates
Methemoglobinemia Associated Agents
QTc-Prolonging Agents (Indeterminate Risk and Risk Modifying)
Drug Info/Drug Targets: DrugBank 3.0: a comprehensive resource for 'omics' research on drugs. Knox C, Law V, Jewison
T, Liu P, Ly S, Frolkis A, Pon A, Banco K, Mak C, Neveu V, Djoumbou Y, Eisner R, Guo AC, Wishart DS.
Nucleic Acids Res. 2011 Jan; 39 (Database issue):D1035-41. | PMID:21059682