Introduction

The respiratory tract represents a varied and complex tissue into which antimicrobial agents need to penetrate. The rational selection of antimicrobial agents for the treatment of respiratory tract infections demands an understanding of their spectra of activity, their time-dependent interactions with micro-organisms and their pharmacokinetic properties. In recent years our knowledge of the interaction between antibiotics and pathogens and of the pharmacokinetics of antimicrobials in the respiratory tract has blossomed, with particular interest in the β-lactams, macrolides and quinolones (the antibiotics most frequently used for the treatment of respiratory infections). The emergence of antibiotic resistance in many respiratory pathogens has now reduced the utility of many previously commonly used antibiotics and has challenged the standard choices in the empirical treatment of infections.

Pharmacokinetics in the respiratory tract

The different pathogens that infect the respiratory tract multiply in different tissue compartments. Some, such as Legionella pneumophila and Chlamydia pneumoniae, are intracellular organisms, whereas others, such as Streptococcus pneumoniae and Haemophilus influenzae multiply extracellularly. It is also possible to distinguish between infection in the air spaces, such as the lumen of the bronchi, bronchioles and alveoli, and infection in the tissues of the bronchial mucosa and alveolar interstitium. For an antimicrobial to be effective in treating respiratory tract infections, an adequate concentration of the antimicrobial agent must be delivered to the particular tissue compartment (if necessary, into the cells themselves) which is the site of bacterial replication.