This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 13. Infectious Diseases Chapter 153. Both drugs block the folic acid metabolism cycle of bacteria and are much more active together than either agent is alone.
Sulfonamides are competitive inhibitors of the incorporation of p -aminobenzoic acid.
TMP prevents reduction of dihydrofolate to tetrahydrofolate. Pseudomonas aeruginosa is usually resistant. Both TMP and SMX are well absorbed orally and are excreted into the urine. TMP-SMX is the drug of choice for treatment of Pneumocystis carinii pneumonia and in prophylaxis of this infection in AIDS patients and children and adults with malignancies. It is useful in treatment of typhoid fever, especially when ampicillin and chloramphenicol cannot be used.