The first widely used quinolone, nalidixic acid, was effective for urinary tract infections because it concentrated in the urine, but had little systemic activity. Fluorination of the quinolone structure was subsequently found to produce compounds that were up to 60 times more active than nalidixic acid and killed a wider range of organisms. They act principally by inhibiting bacterial (but not human) DNA gyrase, so preventing the supercoiling of DNA, a process that is necessary for compacting chromosomes into the bacterial cell; they are bactericidal and exhibit concentration-dependent bacterial killing (see p. 203). In general quinolones are extremely active against Gram-negative organisms including Escherichia coli, Salmonella sp., Shigella sp., Neisseria sp. and Haemophilus influenzae and they have useful activity against Pseudomonas aeruginosa and Legionella pneumophila. They are less active against Gram-positive organisms (resistance commonly emerges) and currently available examples are not effective against anaerobes.
Pharmacokinetics. Quinolones are well absorbed from the gut, and widely distributed in body tissue. Mechanisms of inactivation (hepatic metabolism, renal and biliary excretion) are detailed below for individual members. There is substantial excretion and re-absorption via the colonic mucosa, and patients with renal failure or intestinal malfunction, e.g. ileus, are prone to accumulate quinolones.
Uses vary between individual drugs (see below).
Adverse effects include gastrointestinal upset and allergic reactions (rash, pruritus, arthralgia, photosensitivity and anaphylaxis). CNS effects may develop with dizziness, headache and confusion, and are sufficient to require cautioning the patient against driving a motor vehicle. Convulsions have occurred during treatment (avoid or use with
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