Continuous activity of significant antibiotics.

Respiratory tract infections (RTIs) are the primary cause of antibiotic use in general practice. Since the first penicillin was introduced for therapeutic purposes, several classes of antibiotics have been used in the treatment of community-acquired RTIs. The phase when penicillins G and V could be active in RTIs was relatively short lived due to the early emergence of resistant organisms. Ampicillin and amoxicillin have been used successfully for more than 20 years in the treatment of RTIs. In the late 1950s and 1960s, erythromycin, tetracyclines, and co-trimoxazole were also prescribed for RTIs. In the 1970s, other molecules belonging to the cephalosporin class of antibiotics, such as cephalexin, cephaloglycin, cefadroxil, and cephradine, were introduced in general practice for the same indication. Susceptibility of the predominant respiratory pathogens to these antimicrobial agents lasted for many years. However, Haemophilus influenzae responded poorly to erythromycin, and up to 30% of pneumococcal and streptococcal strains are resistant to macrolides, tetracyclines, and co-trimoxazole. Since 1976, increasing percentages of beta-lactamase producers (up to 20% in 1989) were found among Haemophilus species, and Moraxella catarrhalis, a frequent beta-lactamase producer, is increasingly isolated as a respiratory pathogen. These problems have led to the development of additional compounds, most characterized by their stability in the presence of beta-lactamases, such as amoxicillin + clavulanic acid, or exhibiting relative resistance to enzymatic inactivation, such as cefaclor. Treatment today of most RTIs also takes into account the cost-effectiveness relationship of these antibiotics.