Dirithromycin has an antimicrobial spectrum similar to erythromycin. It has a strong inhibitory effect on chlamydia and mycoplasma. For most Gram-positive bacteria, the activity of Dierythromycin is 2-4 times lower than that of Erythromycin. Dierythromycin was 4 times more active than erythromycin against pertussis bacillus. In vitro antistaphylococcal activity of Dirithromycin is similar to or less than erythromycin. Dirithromycin can inhibit Streptococcus pyogenes and Streptococcus pneumoniae when it is less than or equal to 0.03-0.12 ug/ml. Group B streptococcus was also inhibited at the same concentration. Streptococcus pneumoniae and Listeria were inhibited at 0.12 and 0.5 ug/ml, respectively. Streptococcus A, Listeria and Enterococcus resistant to antibiotics are also resistant to Dirithromycin. The MIC90 of erythromycin-sensitive and resistant Staphylococcus was 0.5 ug/ml and 8 ug/ml. Dirithromycin did not inhibit aerobic Gram-positive bacteria. Generally speaking, the activity of Dirithromycin is 2-4 times higher than that of Erythromycin. The activity of Dirithromycin against Staphylococcus and Streptococcus did not decrease with the addition of human serum. The activity of macrolides is 1-4 times higher at pH 8.0 than at pH 6.0. Dirithromycin has bacteriostatic effect on Staphylococcus aureus and slow bactericidal effect on Haemophilus influenzae. Dirithromycin is resistant to Enterococcus and most methicillin-resistant Staphylococcus aureus, and has close cross-resistance with other macrolides.
