Activity of oral [beta ]-lactam antimicrobial agents versus respiratory tract isolates of , , and in the era of antibiotic resistance

The management of outpatient respiratory tract infections with oral beta-lactam antimicrobial agents has been complicated by the emergence of beta-lactamase-producing strains of Haemophilus influenzae and Moraxella catarrhalis and isolates of Streptococcus pneumoniae that express varying levels of beta-lactam resistance because of altered penicillin-binding proteins. There is no question that all 3 of these important respiratory tract pathogens have changed conspicuously in the context of decreased activity of beta-lactam antimicrobial agents. The question arises, what does this change mean from a clinical perspective? In this review, the in vitro activity of various oral beta-lactam antimicrobial agents versus contemporary isolates of H influenzae, M catarrhalis, and S pneumoniae will be compared. The approach that is used in defining organisms as being susceptible or resistant to beta-lactam antimicrobial agents will be elucidated. Finally, an effort will be made to assess the ramifications of beta-lactam resistance for therapeutic efficacy in patients with respiratory tract infections caused by these 3 bacteria. We conclude that, notwithstanding diminished beta-lactam activity for many clinical isolates of H influenzae, M catarrhalis, and S pneumoniae, certain agents remain effective in treating outpatient respiratory tract infections.