Clindamycin and azithromycin should not be used together. Because the mechanism of antibacterial action of clindamycin and azithromycin is to bind to the 50S subunit of bacterial ribosomes, the combination of the two compete for the binding site of the drug, which will produce antagonistic effects and risk of cross-resistance. Clindamycin is mainly indicated for infections caused by Gram-positive bacteria, such as tonsillitis, suppurative otitis media, sinusitis, acute bronchitis, acute attacks of chronic bronchitis, pneumonia, lung abscess, and also for infections caused by anaerobic bacteria, such as abscess chest, lung abscess, anaerobic pneumonia, intra-abdominal infections such as peritonitis, intra-abdominal abscess, and infections of the female pelvis and genitalia. Azithromycin is mainly indicated for acute pharyngitis and acute tonsillitis caused by Streptococcus pyogenes, sinusitis, otitis media, acute bronchitis caused by sensitive bacteria, and pneumonia caused by Streptococcus pneumoniae and Mycoplasma pneumoniae. The antibacterial spectrum of these two drugs is relatively similar, so they should not be used together.