RT Book, Section A1 Katzung, Bertram G. A1 Kruidering-Hall, Marieke A1 Tuan, Rupa Lalchandani A1 Vanderah, Todd W. A1 Trevor, Anthony J. SR Print(0) ID 1180557975 T1 Sulfonamides, Trimethoprim, & Fluoroquinolones T2 Katzung & Trevor's Pharmacology: Examination & Board Review, 13e YR 2021 FD 2021 PB McGraw-Hill Education PP New York, NY SN 9781260117127 LK accessmedicine.mhmedical.com/content.aspx?aid=1180557975 RD 2024/10/11 AB Sulfonamides and trimethoprim are antimetabolites that are selectively toxic to microorganisms because they interfere with folic acid synthesis in microorganisms but not in mammals. Sulfonamides continue to be used selectively as individual antimicrobial agents, although resistance is common. The combination of a sulfonamide with trimethoprim causes a sequential blockade of folic acid synthesis. This results in a synergistic action against a wide spectrum of microorganisms; resistance occurs but has been relatively slow in development.Fluoroquinolones, which selectively inhibit microbial nucleic acid metabolism, also have a broad spectrum of antimicrobial activity that includes many common pathogens. Resistance has emerged to the older antibiotics in this class but has been offset to some extent by the introduction of newer fluoroquinolones with expanded activity against common pathogenic organisms.