INVITRO ACTIVITY OF DIRITHROMYCIN (LY-237216) COMPARED WITH ACTIVITIES OF OTHER MACROLIDE ANTIBIOTICS

Dirithromycin inhibited Streptococcus pyogenes, Streptococcus pneumoniae, and other hemolytic streptococci at concentrations of ≤ 0.03 to 0.12 μg/ml, with 90% inhibition at 0.12 μg/ml, which is comparable to results using erythromycin. Group A streptococci, listeriae, and enterococci resistant to erythromycin were resistant to dirithromycin. Erythromycin-susceptible staphylococci were inhibited by 0.5 μg/ml, but for erythromycin-resistant isolates MICs were ≥ 8 μg/ml. For Haemophilus influenzae, MICs were ≥ 8 μg/ml, tow- to fourfold greater than for erythromycin. The activity of dirithromycin against staphylococci and streptococci was not decreased by the addition of human serum.