The term quinolone(s) refers to the first generation of the potent and toxic synthetic chemotherapeutic agents derived from chloroquine used to treat serious, complicated and life threatening bacterial infections. Hans Andersag discovered chloroquine, in 1934 at Bayer I.G. Farbenindustrie A.G. laboratories in Eberfeld, Germany. The first generation of the quinolones begins with the introduction of nalidixic acid in 1962 for treatment of kidney infections in humans. This drug was discovered by George Lesher and coworkers in a distillate during chloroquine synthesis.

History

Nalidixic acid is considered to be the predecessor of all members of the quinolone family, including the second, third and fourth generations commonly known as fluoroquinolones. This first generation also included other quinolone drugs such as pipemidic acid, oxolinic acid and cinoxacin, which were introduced in the 1970s. They proved to be only marginal improvements over nalidixic acid. Though it is generally accepted that nalidixic acid is to be considered the first quinolone drug, this has been disputed over the years by a few researchers who believe that chloroquine, from which nalidixic acid is derived, is to be considered the first quinolone drug rather than nalidixic acid.

This class of synthetic chemotherapeutic agents has a broad spectrum of antimicrobial activity as well as a unique mechanism of action resulting in inhibition of bacterial DNA gyrase and topoisomerase IV. However there is considerable concern that this affects the DNA of healthy cells as well.

Since the introduction of nalidixic acid in 1962, more than 10,000 analogs have been synthesized, but only a handful have found their way into clinical practice.

Pharmacology

The basic pharmacore of the fluoroquinolone class is based upon the quinoline ring. The addition of the fluorine atom at C6 is what distinguishes the successive generations, fluoroquinolones, from the first generation, quinolones. It has since been demonstrated that the addition of the C6 fluorine atom is not a necessary requirement for the antibacterial activity of this class (circa 1997).

Various substitutions made to the quinoline ring resulted in the development of numerous fluoroquinolone drugs that we see today. Each substitution is associated with a number of specific adverse reactions, as well as increased activity against bacterial infections, where as the quinoline ring, in and of itself, has been associated with severe and even fatal adverse reactions.

Mechanism

Quinolones and fluoroquinolones are chemotherapuetic bactericidal drugs, eradicating bacteria by interfering with DNA replication. The other antibiotics used today, (e.g., tetracyclines, lincomycin, erythromycin, and chloramphenicol) do not interact with components of eukaryotic ribosomal particle and thus have proven not to be toxic to eukaryotes, as opposed to the fluoroquinolone class of drugs. Safer drugs used to treat bacterial infections, such as penicillins and cephalosporins, inhibit cell wall biosynthesis, thereby causing bacterial cell death, as opposed to the interference with DNA replication as seen within the fluoroquinolone class of drugs.