Chapter 246

The first antibiotic to be discovered was penicillin, a natural product of Penicillium mold. Innumerable microbial products have been investigated since then, and much work has been done in chemically modifying these natural products in an attempt to enhance the benefits while minimizing the undesirable effects. These modified products, termed semisynthetic antibiotics, increased stability and solubility, improved pharmacokinetics (ie, wider distribution and longer half-life), and increased antimicrobial activity. Minimizing the undesirable effects creates antibiotics with decreased toxicity and increased efficacy.

Unfortunately, overuse of this vast array of antibiotics now is one of our most pressing problems. Antibiotics are the most commonly prescribed class of drugs in the United States. In children, antibiotics represent about 30% of all prescribed drugs. Almost half of children under age 15 will have an antibiotic prescribed to them each year.1

Misuse of antibiotics is common. Thirty percent to 65% of antibiotic prescriptions in hospitals are found to be irrational, inappropriate, or of questionable value. In community practice, market research data have determined that 50% of physicians prescribe antibiotics for the common cold, although this trend has improved in recent years.1,2 The reasons for this antibiotic “abuse” are multifactorial, but the desire to help patients, fear of missing a bacterial infection that might respond to antibiotics, and the ease of treating a possible bacterial infection versus considering and investigating an alternative diagnosis all contribute.

One prevalent attitude is that the risk of not treating an infection is greater than the risk of side effects from antibiotic treatment. In fact, approximately 5% of patients taking antibiotics experience side effects, and the indiscriminate use of antibiotics alters the drug-resistance patterns of isolates from the individual being treated and from the environment in general. Furthermore, a potentially more serious infection such as meningitis can be masked by incidental antibiotic therapy.

### Antibiotic Selection

The decision to prescribe an antibiotic is based on proof or strong suspicion that the patient has a bacterial infection. Probable viral infectious or noninfectious processes should not be treated with antibiotics. However, in the critically ill patient in whom there is some chance that a bacterial infection may be a contributing factor, it is prudent to administer antibiotics effective against the most likely pathogens.3

Whenever possible, antibiotic selection should be based on the isolation of a pathogen, but most patients who require antibiotic therapy present with an acute problem that mandates initial empiric therapy. The antibiotic(s) chosen should be based on the pathogens likely to be responsible for the infection, knowledge of local antibiotic sensitivity patterns, and specific host characteristics. If more than one antibiotic is active against the likely pathogens at the site of infection, the specific agent should be chosen on the basis of relative toxicity, convenience of administration, and cost. Once the pathogen is identified, the antibiotic with the most narrow spectrum of activity should be ...

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