Fluoroquinolone antibiotics. Microbiology, pharmacokinetics and clinical use.
The newer fluoroquinolones are a major advance in antimicrobial chemotherapy. They inhibit the supercoiling activity of the DNA gyrase enzyme, thus exerting their antibacterial action on DNA and RNA synthesis, resulting in a biphasic response and killing of susceptible organisms. The newer fluoroquinolones have an extended antimicrobial spectrum compared to their older congeners, and are highly active against most Gram-negative pathogens including the Enterobacteriaceae and Pseudomonas aeruginosa. While Staphylococcus aureus and coagulase-negative staphylococci are usually susceptible to the fluoroquinolones, streptococci are generally more resistant and enterococci are resistant. All of the newer fluoroquinolones may be administered orally and most of them have been administered parenterally. They are widely distributed in the body, attaining therapeutic concentrations in most tissues. All of the fluoroquinolones have long half-lives and may be administered once or twice daily. The fluoroquinolones have proved effective in many infections, including uncomplicated or complicated urinary tract infections, respiratory tract infections, gonorrhoea, bacterial gastroenteritis, and soft tissue infections due to Gram-negative organisms. In general, success has been notable in the management of Gram-negative infections but less so with Gram-positive infections. Resistance has occurred and is proving a problem with P. aeruginosa in some cystic fibrosis patients, but as yet no plasmid-mediated resistance has developed. Cross-resistance occurs between the quinolones but only rarely with other classes of antibacterial drugs. The fluoroquinolones have an excellent safety record and their adverse effects, which include hypersensitivity reactions, dizziness, headache, gastrointestinal disturbance and minor haematological abnormalities are usually mild and transient. However, the fluoroquinolones have been found to damage juvenile weight-bearing joints in animals and are therefore only to be used with caution in children; transient arthralgia has been reported in a cystic fibrotic teenager on long term ciprofloxacin therapy. All of the fluoroquinolones except ofloxacin are associated with a variable increase in the serum concentration of theophylline, warfarin and caffeine. Thus, the fluoroquinolones are an attractive option in the management of many infections. Cost and possible resistance, however, should counsel caution in their use, and may limit them to situations where a cheaper antimicrobial of equivalent efficacy is not available.