Journal of Antimicrobial Chemotherapy (1999) 44, 445-453
© 1999 The British Society for Antimicrobial Chemotherapy
In-vitro activity of HMR 3647 against Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and ß-haemolytic streptococci
Bristol Centre for Antimicrobial Research and Evaluation, Southmead Health Services NHS Trust and University of Bristol, Department of Medical Microbiology, Southmead Hospital, Westbury-on-Trym, Bristol BS10 5NB, UK
The in-vitro activity of HMR 3647 and
seven comparators (azithromycin, clarithromycin, erythromycin A, roxithromycin, penicillin G,
ciprofloxacin and levofloxacin) were tested against 207 Streptococcus pneumoniae and
200 ß-haemolytic streptococci. Ten comparators (azithromycin, clarithromycin,
erythromycin A, roxithromycin, ampicillin, co-amoxiclav, cefuroxime, cefotaxime, ciprofloxacin
and levofloxacin) were tested against 143 Haemophilus influenzae and 58 Moraxella catarrhalis. The MIC50 of HMR 3647 for S. pneumoniae
was 
0.008 mg/L, less than that for the macrolides or quinolones tested. Pneumococci with
an erythromycin A MIC of 0.06 mg/L (n = 23) had an MIC50 of
HMR 3647 0.008 mg/L, whereas isolates with an erythromycin A MIC 
1 mg/L (n = 34) had an MIC50 of HMR 3647 of 0.03 mg/L, a four-fold increase.
In contrast, the difference in macrolide MIC50s for the two groups was 64-fold.
The MIC50s for ß-haemolytic streptococci, classified by Lancefield group, were
in the range 0.015 to 0.06 mg/L for HMR 3647. H. influenzae were categorized into
three groups according to cefuroxime MIC: <1 mg/L (n = 72); 2–4
mg/L (n = 29); and >4 mg/L (n = 42). The MIC50 of HMR 3647 increased two-fold with increasing cefuroxime MICs; ß-lactam MICs
increased much more markedly. The MIC50 of HMR 3647 for M. catarrhalis was 0.03 mg/L. HMR 3647 has good activity against respiratory tract pathogens but in-vitro
susceptibility is affected by erythromycin A susceptibility in S. pneumoniae and
ß-haemolytic streptococci.
* Corresponding author. Tel: +44-117-9595652; Fax: +44-117-9593154.
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