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Trimethoprim Trimethoprim is a diaminopyrimidine, a structural analogue of the pteridine moiety of folic acid. Trimethoprim is a competitive inhibitor of dihydrofolate reductase; this enzyme is responsible for reduction of dihydrofolic acid to tetrahydrofolic acid—the essential final component in the folic acid synthesis pathway. Like that of the sulfonamides, the activity of trimethoprim is compromised in the presence of exogenous thymine or thymidine. Inhibition of Nucleic Acid Synthesis or Activity Numerous antibacterial compounds have disparate effects on nucleic acids. Quinolones The quinolones, including nalidixic acid and its fluorinated derivatives (ciprofloxacin, levofloxacin, and moxifloxacin), are synthetic compounds that inhibit the activity of the A subunit. | Chapter 127. Treatment and Prophylaxis of Bacterial Infections Part 4 Trimethoprim Trimethoprim is a diaminopyrimidine a structural analogue of the pteridine moiety of folic acid. Trimethoprim is a competitive inhibitor of dihydrofolate reductase this enzyme is responsible for reduction of dihydrofolic acid to tetrahydrofolic acid the essential final component in the folic acid synthesis pathway. Like that of the sulfonamides the activity of trimethoprim is compromised in the presence of exogenous thymine or thymidine. Inhibition of Nucleic Acid Synthesis or Activity Numerous antibacterial compounds have disparate effects on nucleic acids. Quinolones The quinolones including nalidixic acid and its fluorinated derivatives ciprofloxacin levofloxacin and moxifloxacin are synthetic compounds that inhibit the activity of the A subunit of the bacterial enzyme DNA gyrase as well as topoisomerase IV. DNA gyrase and topoisomerases are responsible for negative supercoiling of DNA an essential conformation for DNA replication in the intact cell. Inhibition of the activity of DNA gyrase and topoisomerase IV is lethal to bacterial cells. The antibiotic novobiocin also interferes with the activity of DNA gyrase but it interferes with the B subunit. Rifampin Rifampin used primarily against Mycobacterium tuberculosis is also active against a variety of other bacteria. Rifampin binds tightly to the B subunit of bacterial DNA-dependent RNA polymerase thus inhibiting transcription of DNA into RNA. Mammalian-cell RNA polymerase is not sensitive to this compound. Nitrofurantoin Nitrofurantoin a synthetic compound causes DNA damage. The nitrofurans compounds containing a single five-membered ring are reduced by a bacterial enzyme to highly reactive short-lived intermediates that are thought to cause DNA strand breakage either directly or indirectly. Metronidazole Metronidazole a synthetic imidazole is active only against anaerobic bacteria and protozoa. The reduction of metronidazole s
