Quinolones rapidly inhibit DNA synthesis by promoting cleavage of bacterial DNA in the DNA-enzyme complexes of both DNA gyrase and type IV topoisomerase, resulting in rapid bacterial death. Gram-negative bacterial activity correlates with inhibition of DNA gyrase, and gram-positive bacterial activity corresponds with inhibition of DNA type IV topoisomerase.1 The quinolones are categorized into generations based on their antimicrobial activity classification. The first-generation quinolone, nalidixic acid, was introduced in 1962. It is used less often today and has moderate gram-positive coverage and minimal systemic distribution. The second generation has expanded gram-negative coverage, atypical pathogen coverage, but limited gram-positive coverage. The third generation has improved gram-positive coverage and retained gram-negative and atypical activity. The fourth generation has improved gram-positive coverage, gained anaerobic coverage, and maintained gram-negative activity.
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