SummaryA clinical and pharmacological evaluation of erythromycin ethylsuccinate was carried out in 20 patients with acute exacerbations of chronic bronchitis. Administration of a 1 g dose after a meal on Day 1 produced serum concentrations of 3.36μg/ml after 60 min and 3.12μg/ml after 90 min. Serum levels on Day 4 of treatment with 1 g 4-times daily showed an accumulation of erythromycin, concentrations of over 4μg/ml being found at 1 to 2 hours after the first dose. Twelve of the 15 patients with microscopic evidence of pus in the sputum and positive for H. influenzae (12) and/or pneumococci (5) showed a satisfactory response to treatment, as did the other 5 patients with negative cultures. In the 3 patients who failed to respond clinically, H. influenzae was still present on culture and the sputum remained purulent. In 2 patients regarded as clinically cured, the sputum was mucoid but H. influenzae persisted. There was no evidence of patient intolerance of treatment with erythromycin ethylsuccinate.