Antimicrobial therapy: principles of use

Antibiotics are among the most commonly prescribed drugs. They are largely used therapeutically, notably in primary care, but may also be used prophylactically to prevent postoperative sepsis or infection complicating selected medical conditions. Ideally, microbiological documentation of the causative infection should be sought, but in reality most infections are treated empirically. The principles governing choice of agent, dose regimen and duration of therapy should be based on a thorough knowledge of the likely cause of the infection according to its mode of presentation and the circumstances in which it occurs. Antibiotics are considered bactericidal or bacteristatic according to the site of action within the target pathogen. Bactericidal agents are essential in the management of patients with infective endocarditis and in those with severe immunodeficiency, notably neutropenia. The dose and frequency of administration are determined by the pharmacokinetic profile of the drug, the susceptibility of the target pathogens and, increasingly, pharmacodynamic principles reflecting the mathematical relationship between these two parameters. Antibiotic resistance has reached worrying levels in selected pathogens, notably pneumococci, MRSA and Gram-negative enteric pathogens. Few new agents are under development; hence, the importance of prudent prescribing based on sound principles.