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Quinolones: Effects, Uses and Risks

Quinolones are a group of synthetic antibiotics used to treat a wide range of bacterial infections. They work by inhibiting key bacterial enzymes involved in DNA replication.

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Things worth knowing about "Quinolones"

Quinolones are a group of synthetic antibiotics used to treat a wide range of bacterial infections. They work by inhibiting key bacterial enzymes involved in DNA replication.

What Are Quinolones?

Quinolones are a class of synthetic antibiotics that have been used in medicine since the 1960s. They are among the most widely prescribed antibiotics worldwide and are characterized by a broad spectrum of activity against gram-negative and, in newer generations, also gram-positive bacteria. The group includes older agents such as nalidixic acid as well as modern fluoroquinolones like ciprofloxacin, levofloxacin, and moxifloxacin.

Mechanism of Action

Quinolones interfere with the DNA replication of bacteria by inhibiting two essential bacterial enzymes:

DNA gyrase (topoisomerase II): the primary target in gram-negative bacteria
Topoisomerase IV: the primary target in gram-positive bacteria

By inhibiting these enzymes, quinolones cause double-strand breaks in bacterial DNA, leading to bacterial cell death (bactericidal effect). Because human cells use different topoisomerases, quinolones act selectively against bacteria.

Generations and Indications

Quinolones are classified into four generations, each with an expanded spectrum of activity:

1st Generation

Agents such as nalidixic acid were primarily active against gram-negative organisms and mainly used for uncomplicated urinary tract infections. They are now largely obsolete.

2nd Generation

Fluoroquinolones such as ciprofloxacin and norfloxacin have a significantly broader spectrum and are used for urinary tract infections, respiratory infections, gastrointestinal infections, and musculoskeletal infections.

3rd Generation

Levofloxacin shows additional activity against gram-positive organisms such as Streptococcus pneumoniae and is frequently used for community-acquired pneumonia.

4th Generation

Moxifloxacin has a very broad spectrum that includes anaerobes and atypical pathogens. It is used in severe respiratory tract infections and complicated skin and soft tissue infections.

Side Effects and Risks

Despite their efficacy, quinolones can cause a number of side effects. The European Medicines Agency (EMA) has issued important safety warnings in recent years:

Gastrointestinal complaints: nausea, vomiting, diarrhea
Central nervous system effects: insomnia, dizziness, headaches, and rarely seizures
Tendon damage: increased risk of tendinitis and tendon rupture, especially of the Achilles tendon
Phototoxicity: increased sensitivity of the skin to sunlight
QT interval prolongation: cardiac arrhythmias (particularly with moxifloxacin)
Peripheral neuropathy: tingling, numbness, or pain in the hands and feet
Aortic aneurysm: rare but serious risk of bulging of the main artery

Contraindications and Drug Interactions

Quinolones are contraindicated in:

Patients with known hypersensitivity to quinolones
Children and adolescents during growth phases (risk of cartilage damage)
Pregnancy and breastfeeding
Patients with epilepsy or a lowered seizure threshold

Important drug interactions include:

Antacids (e.g., aluminium or magnesium salts): reduce absorption of quinolones
Iron supplements: also reduce absorption
NSAIDs (non-steroidal anti-inflammatory drugs): increased risk of seizures
Anticoagulants (e.g., warfarin): enhanced bleeding tendency

Antibiotic Resistance

The widespread use of quinolones has contributed to a significant increase in antibiotic resistance. Resistant bacterial strains arise through mutations in target genes (gyrase, topoisomerase IV) or through active efflux mechanisms. To prevent resistance, quinolones should only be used when clearly indicated and, where possible, guided by susceptibility testing.

References

European Medicines Agency (EMA) - Safety review of fluoroquinolones and quinolones (2019). Available at: https://www.ema.europa.eu
World Health Organization (WHO) - Antimicrobial Resistance: Global Report on Surveillance (2014). Available at: https://www.who.int
Brunton, L. L. et al. - Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th edition, McGraw-Hill (2018).

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