Fluoroquinolones, trimethoprim-sulfamethoxazole, nitroimidazoles and nitrofurantoin
How fluoroquinolones, trimethoprim-sulfamethoxazole, metronidazole and nitrofurantoin damage bacterial DNA or folate synthesis, and the mechanisms behind their key toxicities, interactions and laboratory effects, including the TGA boxed warning for fluoroquinolones.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Fluoroquinolones (ciprofloxacin, moxifloxacin, norfloxacin) trap DNA gyrase and topoisomerase IV on cleaved DNA. They are concentration dependent, have high oral bioavailability, and carry a TGA boxed warning (2025) for disabling tendon, nerve and CNS effects.
- Trimethoprim-sulfamethoxazole (TMP-SMX) blocks two steps in bacterial folate synthesis. Trimethoprim blocks ENaC and tubular creatinine secretion, so expect a rising potassium and creatinine.
- Metronidazole is a prodrug activated only by anaerobic electron carriers.
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Sources
- Therapeutic Guidelines: AntibioticAU/NZTherapeutic Guidelines Limited
- Australian Medicines HandbookAU/NZAustralian Medicines Handbook Pty Ltd, 2026
- Strengthened warnings for broad-spectrum antibiotics (fluoroquinolones)AU/NZTherapeutic Goods Administration, 2025
- Goodman & Gilman's The Pharmacological Basis of Therapeutics (14th ed.)McGraw Hill (Brunton and Knollmann, 2023), 2023
- APO-Ciprofloxacin (ciprofloxacin) Australian product informationAU/NZTherapeutic Goods Administration, 12 November 2026
- Avelox (moxifloxacin) Australian product informationAU/NZTherapeutic Goods Administration, 11 August 2025
- Last updated
- 14 November 2026
What changed
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