Amoxicillin-clavulanic acid in the treatment of lower respiratory tract infections caused by beta-lactamase-positive Haemophilus influenzae and Branhamella catarrhalis.

Twenty-one adult patients hospitalized with lower respiratory tract infections due to Branhamella catarrhalis or Haemophilus influenzae or both were treated with the combination of oral amoxicillin and potassium clavulanate (Augmentin) in an open, noncomparative clinical trial. Diseases included pneumonia, empyema, and exacerbations of bronchiectasis and chronic lung disease. Thirteen of 16 B. catarrhalis and six of nine H. influenzae isolates were beta-lactamase positive. The patients with B. catarrhalis were treated for a mean of 5.3 days, and those with H. influenzae were treated for a mean of 7.0 days. The overall response to therapy was excellent, with 18 of 19 beta-lactamase-producing strains eradicated on therapy. One patient secondarily infected with Pseudomonas aeruginosa was a clinical failure, and two patients with H. influenzae who became culture positive again after therapy were considered microbiologic failures. Gastrointestinal side effects (especially nausea) were common, although all patients completed a course of therapy. Sputum levels of amoxicillin were surprisingly low (less than 0.05 to 0.54 micrograms/ml), a finding which may explain the high relapse rate (22%) seen with H. influenzae, as these are below the usual MICs of amoxicillin for this organism. The combination of amoxicillin plus potassium clavulanate appears to be an excellent drug for treatment of beta-lactamase-producing strains of these two species, although mild gastrointestinal side effects are common.