Review
How antibiotics can make us sick: the less obvious adverse effects of antimicrobial chemotherapy

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Summary

Antimicrobial agents are associated with side-effects, which are usually tolerated because the benefits of treatment outweigh the toxic effects. Clinicians know about these side-effects but are less likely to understand additional adverse events, such as the overgrowth of resistant microorganisms. Overgrowth can itself precipitate a secondary infection, which can be more difficult to treat. Resistant organisms then spread to other patients and the environment, and contribute to increasing antimicrobial resistance worldwide. Organisms exposed to antibiotics undergo molecular changes that might enhance virulence. Enhanced pathogenicity would affect patients, particularly if the organism is also multiply resistant. Clinicians have a responsibility to select the correct antibiotic as soon as they have diagnosed infection, but an absence of microbiological understanding and ignorance of the potential environmental effects have contributed to inappropriate prescribing. The less obvious results of antimicrobial consumption probably go unrecognised in routine clinical care.

Section snippets

Overgrowth of resistant organisms

Naturally resistant organisms proliferate in response to antibiotic treatment.9 This proliferation can be shown in healthy volunteers and patients, and has been reviewed elsewhere.10 Perhaps the best-known examples are the overgrowth of Candida albicans after almost any antibiotic (figure 1).11 The cephalosporins, in particular, are associated with Candida and also Clostridium difficile-associated diarrhoea; these drugs also encourage overgrowth with enterococci and Pseudomonas aeruginosa (see

Are resistant organisms more virulent?

Treating an infected patient with an antibiotic that is ineffective against the causative organism can complicate clinical management. Signs and symptoms of infection can worsen if the original pathogen is not eradicated,5 not only because bacteria tend to proliferate rapidly if unchecked, but also because proliferation is further enhanced after inappropriate treatment owing to the removal of competing flora. Thus, the pathogen is allowed access to space and nutrients that it might previously

Medical education

There has been a gross reduction in the teaching of pathology, including microbiology, for undergraduate students and there is little in place for postgraduate students. It is time that the risk to public health from inappropriate prescribing was addressed.74 Above all, doctors should understand why antimicrobial agents should only be used when really needed, and why they should choose narrow-range agents. Specialist pharmacists working in conjunction with local microbiologists are helping to

Conclusion

Appropriate antimicrobial prescribing has not yet become a priority for all doctors. It is probable that such prioritisation will become mandatory, after increasing interest from government, lawyers, and the media. Patients have died because they were given the wrong antibiotic (panel).100 Any attempt to curb resistance, however, will have to take into account the fact that resistance genes might be easy to get, but they are also hard to lose.101, 102 It is possible that our generation will

Search strategy and selection criteria

Data for this review were identified by searching the PubMed database (National Library of Medicine) and the Reservoirs of Antibiotic Resistance Network (ROAR) bibliography: (http://www.tufts.edu/med/apua/ROAR/biblio.htm)*. The search terms “antimicrobial resistance/consumption”, “selection”, and “overgrowth” were used. Search criteria encompassed any article, in any language, demonstrating the less obvious adverse effects of antibiotics; and also articles attempting to address inappropriate

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