Mechanism of action of fluoroquinolones is:

FLUOROQUINOLONES: These are quinolone antimicrobials having one or more fluorine substitutions. The &;first generation&; fluoroquinolones (FQs) introduced in 1980s have one fluoro substitution. In the 1990s, compounds with additional fluoro and other substitutions have been developed-fuher extending antimicrobial activity to gram-positive cocci and anaerobes, and/ or confering metabolic stability (longer Ph). These are referred to as second generation&; FQs. Mechanism of action The FQs inhibit the enzyme bacterial DNA gyrase, which nicks double-stranded DNA, introduces negative supercoils and then reseals the nicked ends. This is necessary to prevent excessive positive supercoiling of the strands when they separate to permit replication or transcription. The DNA gyrase consists of two A and two B subunits: The A subunit carries out nicking of DNA, B subunit introduces negative supercoils and then A subunit reseals the strands. FQs bind to A subunit with high affinity and interfere with its strand cutting and resealing function. Recent evidence indicates that in gram-positive bacteria the major target of FQ action is a similar enzyme topoisomerase IV which nicks and separates daughter DNA strands after DNA replication. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:688