The quinolones are a group of relatively new antimicrobials that were originally used primarily to treat patients with urinary tract infections.
For now, the names of the drugs in this class are easy to recognize. It is hoped the new ones that appear in the next few years will also be easy to recognize.
The quinolones inhibit DNA synthesis through a specific action on DNA gyrase.
These drugs inhibit DNA gyrase and, thus, DNA synthesis. DNA gyrase is the bacterial enzyme that is responsible for unwinding and supercoiling of the DNA. This is the only class of antibacterials that inhibits DNA replication. This is a more common approach for the antivirals and the anticancer drugs.
Quinolones are used to treat genitourinary, respiratory, GI, and some skin and soft tissue infections.
These drugs are considered to be broad-spectrum antimicrobial agents. Nalidixic acid was the first available and it is an effective urinary tract antiseptic (it sterilizes the urine). The newer agents in this group are useful in a wide range of bacterial infections, including lower respiratory tract infections, bone and joint infections, and prostatitis. Some are effective against Pseudomonas aeruginosa and are orally active.
Methenamine is metabolized to formaldehyde and ammonia and is used in urinary tract infections.
If you are simply overloaded at this point, skip this drug. Methenamine is an interesting example of a prodrug. The parent compound is not active. In acidic pH, it is hydrolyzed to ammonia and formaldehyde. The formaldehyde is lethal to bacteria. Therefore, this is another bactericidal drug. Methenamine is usually administered as a salt of an acid to help keep the pH of the urine less than 5.5, which is vital for the effective use of methenamine.