Antibiotics are commonly classified based on their mechanism of action, chemical structure, or spectrum of activity. Most antibiotics target bacterial functions or growth processes. Antibiotics that target the bacterial cell wall (penicillins, cephalosporins), or cell membrane (polymixins), or interfere with essential bacterial enzymes (quinolones, sulfonamides) are usually bactericidal in nature. Those that target protein synthesis, such as the aminoglycosides, macrolides, and tetracyclines, are usually bacteriostatic. Further categorization is based on their target specificity: "Narrow-spectrum" antibiotics target particular types of bacteria, such as Gram-negative or Gram-positive bacteria, whereas broad-spectrum antibiotics affect a wide range of bacteria. In the last few years, three new classes of antibiotics have been brought into clinical use. This follows a 40-year hiatus in discovering new classes of antibiotic compounds. These new antibiotics are of the following three classes: cyclic lipopeptides (daptomycin), glycylcyclines (tigecycline), and oxazolidinones (linezolid). Tigecycline is a broad-spectrum antibiotic, whereas the two others are used for Gram-positive infections. These developments show promise as a means to counteract the bacterial resistance to existing antibiotics.
Production
Since the first pioneering efforts of Florey and Chain in 1939, the importance of antibiotics to medicine has led to much research into discovering and producing them. The process of production usually involves the screening of wide ranges of microorganisms, and their testing and modification. Production is carried out using fermentation, usually in strongly aerobic form.
Administration
Oral antibiotics are simply ingested, while intravenous antibiotics are used in more serious cases, such as deep-seated systemic infections. Antibiotics may also sometimes be administered topically, as with eye drops or ointments.
Side effects
Although antibiotics are generally considered safe and well-tolerated, they have been associated with a wide range of adverse effects. There are various side-effects that can be very serious depending on the antibiotics used and the microbial organisms targeted. The safety profiles of newer medications may not be as well established as those that have been in use for many years. Adverse effects can range from fever and nausea to major allergic reactions including photodermatitis and anaphylaxis.[citation needed] One of the more common side-effects is diarrhea, resulting from the antibiotic's disrupting the normal balance of the intestinal flora. This diarrhea is sometimes caused by the anaerobic bacterium Clostridium difficile. Such overgrowth of pathogenic bacteria may be alleviated by ingesting probiotics during a course of antibiotics.[citation needed] The population of bacteria present in the normal vaginal flora may also be disrupted, and may lead to overgrowth of yeast species of the genus Candida in the vulvo-vaginal area. Other side-effects can result from interaction with other drugs, such as elevated risk of tendon damage from administration of a quinolone antibiotic with a systemic corticosteroid. Certain antibiotics administered by IV (e.g.aminoglycosides, vancomycin) can cause significant permanent hearing loss.
