Activity of erythromycin against Haemophilus influenzae from respiratory tract infections.

Abstract

Ampicillin and amoxycillin are very frequently used for treating respiratory infections due to Haemophilis influenzae, but the emergence of beta-lactamase producing strains of this organism may limit their use. Erythromycin would be a suitable alternative but to date variable absorptions and reported minimal inhibitory concentrations (MICs) outside the range of achievable blood levels of erythromycin have prevented its use. The purpose of this study was to determine the MICs of erythromycin for strains of H. influenzae isolated from patients with lower respiratory tract infection and the frequency of beta-lactamase production in these strains. Eighty-five of 100 strains were sensitive to erythromycin (MIC much less than 2.00 mg/L). Eleven strains were resistant to ampicillin and 10 of these produced beta-lactamase. Nine beta-lactamase producing strains had MICs to erythromycin of 2.0 mg/L or less. With the blood levels of erythromycin obtainable with new formulations, this antibiotic should prove of use in the treatment of respiratory infections due to H. influenzae.