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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Fluoroquinolones

Bactericidal antibiotics that trap DNA gyrase and topoisomerase IV on cut DNA. Powerful, but with tendon, nerve and QT warnings.

Updated 2026-11-01

## What they are

Synthetic antibiotics (ciprofloxacin, levofloxacin, moxifloxacin, ofloxacin) that kill bacteria quickly and are very well absorbed by mouth. Ciprofloxacin is strongest against gram-negatives such as Pseudomonas; levofloxacin and moxifloxacin, the «respiratory» quinolones, also cover pneumococcus.

## Mechanism of action

They bind the complex of DNA with DNA gyrase (mainly in gram-negatives) or topoisomerase IV (mainly in gram-positives) after the enzyme has cut both strands. The enzyme is trapped on broken DNA, replication forks collide with it and the double-strand breaks kill the cell. Resistance comes from mutations in gyrA/parC, efflux and plasmid qnr genes.

Target: Bacterial DNA gyrase and topoisomerase IV (type II topoisomerases)

## Key points

- Boxed warning: tendinitis and tendon rupture (more in older people and with corticosteroids), peripheral neuropathy, CNS effects and worse myasthenia gravis.
- Prolong the QT interval and can cause low or high blood sugar; aortic aneurysm and dissection have been linked to them.
- Polyvalent cations (antacids, calcium, iron, zinc) bind them in the gut; they are spaced apart.
- Ciprofloxacin inhibits CYP1A2: theophylline and tizanidine levels rise (tizanidine is contraindicated).
- Levofloxacin and moxifloxacin are WHO-listed medicines for drug-resistant tuberculosis.

## Drugs in this class

- [**Ciprofloxacin** The fluoroquinolone most active against gram-negatives such as Pseudomonas. Used for kidney, prostate and gut… Bacterial DNA gyrase and topoisomerase IV](https://durgical.com/en/pharmacology/ciprofloxacin/)
- [**Levofloxacin** A «respiratory» fluoroquinolone that covers pneumococcus and atypical bacteria, fully absorbed by mouth and also used… Bacterial topoisomerase IV and DNA gyrase](https://durgical.com/en/pharmacology/levofloxacin/)
- [**Moxifloxacin** A respiratory fluoroquinolone with anaerobic activity, cleared mostly by the liver. A WHO medicine for drug-resistant… Bacterial DNA gyrase and topoisomerase IV](https://durgical.com/en/pharmacology/moxifloxacin/)
- [**Ofloxacin** A fluoroquinolone mostly used today as eye and ear drops. Its active half, levofloxacin, replaced it for systemic use. Bacterial DNA gyrase and topoisomerase IV](https://durgical.com/en/pharmacology/ofloxacin/)

## Others in the class

- norfloxacin
- delafloxacin
- gemifloxacin

## Test yourself

Think of the answer, then tap the question to see it.

## What do fluoroquinolones trap?

DNA gyrase or topoisomerase IV bound to DNA that has been cut, producing lethal double-strand breaks.

## Which musculoskeletal adverse effect is in the boxed warning?

Tendinitis and tendon rupture, especially of the Achilles tendon.

## Why are fluoroquinolones spaced from antacids?

Aluminium, magnesium, calcium and iron chelate them and sharply reduce absorption.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - CIPROFLOXACIN tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fa32aafd-e3f5-4be6-9413-c7663c1c2cec) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - LEVOFLOXACIN tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d98cf024-51fa-45a1-b247-da55aba88ca0) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - MOXIFLOXACIN HYDROCHLORIDE tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=54377276-96bf-4140-9e90-55623ab6b013) (DailyMed (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/?query=levofloxacin) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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