Quinolones

The first quinolone - nalidixic acid - was introduced in 1962. Since then, structural modifications have resulted in second, third and fourth-generation fluoroquinolones which have improved coverage of Gram-positive organisms.
Quinolones rapidly inhibit DNA synthesis by promoting cleavage of bacterial DNA. This results in rapid bacterial death.¹ The quinolones exhibit concentration-dependent bacterial killing. The effects of most combinations of antibiotics with quinolones are indifferent or additive, however ciprofloxacin and rifampicin appear to be antagonistic against Staphylococcus aureus.The majority of quinolones are excreted renally.

• Ciprofloxacin - active against Enterobacteriaceae, atypical pathogens, Pseudomonas aeruginosa
• Levofloxacin
• Nalidixic acid - active against Enterobacteriaceae. It has only narrow Gram-negative coverage. Not for use in systemic infections.
• Norfloxacin - active against Enterobacteriaceae. Improved Gram-negative coverage compared with first-generation quinolones. Limited Gram-positive coverage. Not for use in systemic infections.
• Ofloxacin - active against Enterobacteriaceae and atypical pathogens.

The quinolones can be classified into four generations based on antimicrobial activity:²

• First generation:
  • Nalidixic acid
• Second generation:
  • Class I - Norfloxacin
  • Class I I - Ofloxacin, Ciprofloxacin
• Third generation:
  • Levofloxacin
• Fourth generation:
  • Trovafloxacin

Ofloxacin and ciprofloxacin

• Complicated urinary tract and catheter-related infections:
  • Complicated urinary tract infections include those in patients with stones or obstructive uropathies and in patients with catheter-related infections.
  • Ciprofloxacin has been shown to be more effective than trimethoprim-sulfamethoxazole and aminoglycosides in 7 to 10 day courses for the treatment of complicated urinary tract infections.³
• Gastroenteritis with severe diarrhoea:
  • Traveller's diarrhoea caused by Shigella spp., enterotoxigenic E. coli or Campylobacter spp..
  • Ciprofloxacin and ofloxacin are the agents of choice for treatment of enteric typhoid fever.
• Prostatitis:
  • Quinolones are effective in the treatment of prostatitis because of their excellent penetration into prostatic tissue.⁴
• Nosocomial infections
• Sexually transmitted diseases:
  • Pelvic inflammatory disease is usually a result of more than one organism.
  • Monotherapy is incomplete. Quinolone treatment options include:
    • Ofloxacin plus metronidazole
    • Ofloxacin plus cefoxitin
    • Ciprofloxacin plus clindamycin⁵

Not for use in community-acquired pneumonia because of associations with pneumococcal bacteraemia and meningeal seeding, due to poor pneumococcal susceptibility.

Levofloxacin

• Community-acquired pneumonia in hospitalised patients or if atypical pathogens are strongly suspected
• Community-acquired pneumonia in non-hospitalised patients with risk factors for resistant pneumococcal infection

Trovafloxacin

• Atypical pathogens
• Methicillin-susceptible Staphylococcus aureus, Streptococci
• Anaerobes
• Improved Gram-positive coverage over third generation quinolones and added anaerobic coverage also. May be useful in intra-abdominal infections.

They are also used in post-exposure prophylaxis for anthrax, cholera, plague (Yersinia pestis) and tularaemia.

Gastrointestinal and central nervous system effects e.g. headaches, dizziness, drowsiness, are the most frequent side effects.

• Gastrointestinal:
  • Nausea, vomiting, diarrhoea, abdominal pain
• CNS:
  • Headache, dizziness, drowsiness, confusion, insomnia, fatigue, malaise, depression, somnolence, seizures, vertigo, lightheadedness, restlessness, tremor
• Dermatological:
  • Rash, photosensitivity reactions, pruritus
• Prolongation of QT interval
• Hepatotoxicity
• Abnormal or bitter taste
• Tendon rupture:
  • CSM advises that patients taking quinolones who experience tendon pain or inflammation, should discontinue treatment and rest the limb
• Increased serum digoxin levels
• Myasthenia gravis may be exacerbated by quinolones