antibioticsbooks

42 PART 1 Antibiotic Therapy
cross-reactivity are available for beta-lactam drugs,
estimates for cross-reactivity within other classes
(for example, between fluoroquinolones) are essentially
nonexistent. Because labeling a patient with
an allergy to a particular antibiotic can limit future
treatment options severely and possibly lead to
the selection of inferior drugs, every effort should
be made to clarify the exact nature of a reported
allergy.
Antibiotic Toxicities
Despite being designed to affect the physiology of
microorganisms rather than humans, antibiotics
can have direct toxic effects on patients. In some
cases, this is an extension of their mechanism of
action when selectivity for microorganisms is not
perfect. For example, the hematologic adverse
effects of trimethoprim stem from its inhibition
of folate metabolism in humans, which is also
its mechanism of antibiotic effect. In other cases,
antibiotics display toxicity through unintended
physiologic interactions, such as when vancomycin
stimulates histamine release, leading to its characteristic
red man syndrome. Some of these toxicities
may be dose related and toxicity often occurs when
doses are not adjusted properly for renal dysfunction
and thus accumulate to a toxic level. Proper
dosage adjustment can reduce the risk of doserelated
toxicities.
Superinfection
The human body is colonized by a variety of
bacteria and fungi. These organisms are generally
considered commensals, in that they benefit