Combination antimicrobial that synergistically inhibits the sequential steps of bacterial tetrahydrofolate synthesis necessary for microbial purine and DNA production.
Resistance to Gram-negative organisms has markedly increased, limiting its use against infections by such organisms.
Trimethoprim is similar to the potassium sparing diuretic amiloride and reduces urinary potassium excretion by approximately 40%.
The use of trimethoprim-sulfamethoxazole in older patients with ace inhibitors or ARB’s is associated with an increased risk of hyperkalemia relative to other antibiotics.