Principles of antibiotic use

Published on 27/02/2015 by admin

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Chapter 64 Principles of antibiotic use

The intensive care unit (ICU) is always the area of any hospital associated with the greatest use of antibiotics. Much of this high usage is unavoidable, but the clinician working in the ICU must realise that there is an essential consequence of this use. Antibiotic use which should eliminate susceptible organisms promotes (over)growth of other, non-susceptible organisms, especially fungi. As far as bacteria are concerned, antibiotics confer enormous selective advantage to resistant strains, and therefore these strains will congregate where their advantage is greatest, in the ICU. Resistance (and fungal overgrowth) is a direct consequence of usage, and every course of inappropriate antibiotics should be avoided to help reduce the burden of resistance.

Antibiotic stewardship1 has been suggested as a new strategy to help limit resistance. This involves selecting an appropriate drug and optimising its dose and duration to cure an infection while minimising toxicity and conditions for selection of resistant bacterial strains. Inadequate doses of even the ‘correct’ antibiotic may lead to survival of initially susceptible organisms.2,3 For the optimal use of antibiotics not only should antibiotic pharmacokinetics be understood, but there should be clear and rational principles on which each specific antibiotic prescription in the ICU is based. Also, it is probably better to have portions of the ICU population receive different classes of antibiotics at the same time.

Although this chapter will provide basic principles for most of the antibiotic classes commonly used in the ICU, some important antimicrobial agents will not be specifically addressed here, namely macrolides, clindamycin and the antifungal agents.

GENERAL PRINCIPLES48

5 Whilst there should be an attempt to use a narrow-spectrum antibiotic whenever practicable, appropriate therapy, particularly for empirical choice for nosocomial sepsis, mandates initial broad-spectrum antibiotics, even a combination, until culture results are back,12 at which time de-escalation should be embarked upon (see below). Inappropriate and/or delayed correct antibiotic use in the ICU has been shown to have an impact on morbidity and mortality12,13 (Table 64.1).
16 Antibiotic guidelines are only one aspect of infection control.20 Hand-washing and hand hygiene in general are vital and fundamental aspects of infection control.20 Identification and elimination of reservoirs of infection, blocking transmission of infection, barrier nursing, interrupting progression from colonisation to infection and eliminating risk factors such as invasive devices are also important.

Table 64.1 New paradigm of treatment for nosocomial sepsis

Old New
Start with penicillin Get it right first time (broad-spectrum)
Cost-efficient low dose Hit hard up front
Low doses = fewer side-effects Low dose → resistance
Long courses ≥ 2 weeks Seldom longer than 7 days