A group of chemically related synthetic ANTIBIOTICS. Examples include nalidixic acid, ciprofloxacin and norfloxacin which are effective in treating uncomplicated urinary-tract, respiratory-tract and gastrointestinal infections. While they are usually effective against many gram-negative and gram-positive bacteria (see GRAM'S STAIN) METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA) – are resistant to quinolones.