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Bob Kahrs: Antibiotics and antibacterials

Posted: October 18, 2012 - 12:00am

Dear Dr. Bob: My question is: What are antibiotics?

Response: Antibiotics, an early name for antibacterial drugs once included just substances derived from living organisms. They were soon synthesized and called antibacterials. Now, both terms are used to identify drugs that kill or slow the growth of bacteria.

Until 1935, there were few effective antibacterial drugs that could safely be circulated in the body. Thus, it was believed internal bacterial infections could not be treated because existing drugs, like iodine and alcohol were toxic if taken internally. This concern was toppled by discovery that sulfanilamides killed bacteria and sulfa drugs emerged to treat bacterial infections. They have been largely replaced by less toxic antibacterials.

Penicillin, the prototype antibiotic, was discovered in 1920 by Sir Alexander Fleming who noticed that molds secreted bacteria inhibiting substances (penicillin’s). This discovery remained theoretical until 1939 when British scientists adopted penicillin for body-wide treatment of wound-acquired infections and techniques emerged for its mass production.

Thus, World War II and penicillin provided a previously unimagined arsenal of therapeutic agents that can kill or slow growth of infections. However, these compounds, commonly called antibacterials, are not effective against viruses and their use requires identification of infecting organisms and choice of effective products; adequate dosages; appropriate administration; caution about drug interactions and side effects; and symptomatic treatment of infection-produced effects like dehydration, vomiting, or diarrhea. These precautions are challenging.

Some antibacterials include penicillins, sulfonamides, tetracyclines, cephalosporins, polymixins, quinolones, aminoglycocides, glyclocyclines, and oxazlidinones.

In animals, antibacterials are used both to treat infections and as growth accelerating feed additives for livestock. This practice is controversial because of suggestions that it contributes to emergence of antibiotic-resistant microorganisms of importance in human medicine. This controversy continues.

A bi-weekly feature, Farm Animal Health, is provided by Dr. Robert F. Kahrs. It addresses farm animal and equine health. Send questions to:

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