100 Chemical Myths by Lajos Kovács Dezső Csupor Gábor Lente & Tamás Gunda

Author:Lajos Kovács, Dezső Csupor, Gábor Lente & Tamás Gunda
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Fig. 3.38Two natural antibiotics: the relatively simple benzylpenicillin, and daptomycin, which is complex both in its chemical structure and physiological effects. (Authors’ own work)

The discovery of penicillin caused a surge of research on fungi -produced antibiotics . These natural compounds were called antibiotics to distinguish them from chemotherapeutic agents . The use of both terms changed as time went on. Today chemotherapy primarily means cancer treatment with drugs, whereas antibiotics are compounds or substances used against bacterial infection, irrespective of their origin. Antibiotics today include semisynthetic compounds, made by modifying naturally occurring molecules to enhance their efficiency, and fully synthetic products as well.

Nowadays, antibiotics are primarily classified according to the mechanism of their action, with similarity of chemical structure as a secondary factor. Penicillin and its derivatives inhibit the formation of bacterial cell walls (Fig. 3.38). Cephalosporins have the same active mechanism. Other compounds are taken up into bacterial DNA to form unstable molecules (quinolones , metronidazole ) or inhibit peptide synthesis (tetracyclines , aminoglycosides , macrolides ). Some antibiotics (e.g. glycopeptides ) exert a complex effect .

A fair number of antibiotics are natural or are prepared by minor modifications of natural compounds . This fact itself does not guarantee the lack of harm. For medicines, selectivity is critical, although in a few cases, even compounds with severe side effects are used in practice. Patients suffering from bronchial catarrh of bacterial origin are usually willing to face digestive disorders or diarrhea as a price of a speedy recovery. Interestingly, the primary source of these side effects is still not the action of drug on the human body: the antibiotics tend to kill useful intestinal bacteria , which aid digestion. A life threatening illness may even make bad side effects seem tolerable. Some antibiotics cause hearing loss or kidney damage , but the risk from these is still lower than from the lack of treatment. Carefully chosen doses usually minimize the risks of the treatment. If a substance is easily overdosed, its blood levels are continuously monitored and the doses are tailored to the specific needs.

The biggest single risk of antibiotics use today is generating resistant strains of bacteria . The rules of evolution work here as well, and mutations can produce pathogens that are no longer sensitive to a given antibiotic. If the treatment is insufficient, these resistant varieties can survive. One way to fight resistance would be to ensure that all the pathogens are killed by the treatment every time. This is easier said than done. When the doctor selects an antibiotic for treatment, usually nothing is known about the pathogen ’s resistance history. This can be tested in laboratory experiments, but those take time and the patient does not improve in the meantime. Usually, the doctor relies on her or his own experience with a particular type of disease in choosing a medicine. If this does not have an effect, a different one with a substantially different mechanism of action is selected again and again until an effective drug is found.

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