3rd August 2023

Quinolones

Mechanism of action

Bactericidal antibiotics inhibit DNA topoisomerase and gyrase enzymes to prevent DNA replication. Nearly all quinolone antibiotics have a fluorine atom attached and hence are known as fluoroquinolones.

Spectrum of activity

The two most commonly used are ciprofloxacin and levofloxacin. Ciprofloxacin has activity against both Gram positive and negative bacteria; although not anaerobic organisms, and is limited in treating infection caused by Streptococcus pneumoniae and Enterococcus faecalis. It is also active against some mycobacteria. Ciprofloxacin is often used for GI tract infections (including typhoid fever), bone and joint infections, gonorrhoea, and sepsis caused by sensitive organisms. Levofloxacin has better Gram positive activity than ciprofloxacin and can treat atypical infections. Many Staphylococci are resistant to quinolones and therefore have no use in MRSA infections.

Important side effects, interactions and monitoring

QT interval prolongers, so best avoided if patients are taking other drugs, which may also prolong the QT interval. Not recommended for pregnant women. Dose reductions are required in patients with renal impairment, and local guidelines should be consulted.