The quinolones are a set of broad-spectrum antibiotics with notable activity against Gram-negative bacteria. The class has been researched for over 50 years, with the core structure discovered as an impurity in industrial chloroquine synthesis eventually leading Sterling Drug Company to the first-in-class drug nalidixic acid. Alterations of the functionality about the quinolone core have led to the development of several generations of compounds, with early generations active against Gram-negative bacteria such as Pseudomonas, and some Gram-positive bacteria such as Staphylococcus aureus.The Quinoline Metabolite Set 1 contains important examples of first and second generation quinolones, together with nalidixic acid. Ofloxacin and ciprofloxacin are the most widely used members of this generation.