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Cethromycin binds to the 50S subunit of the bacterial ribosome to inhibit both ribosome assembly and bacterial protein synthesis. Adverse effects such as diarrhea, nausea, vomiting, and headache may be due to off-target inhibition of molecules within mammalian cells.

Respiratory tract infections can be caused by numerous strains of bacteria, requiring careful consideration of treatment and antibiotics effective against a broad spectrum of potential pathogens. Cethromycin, like other macrolide antibiotics, binds to the 23S rRNA of the 50S subunit of the bacterial ribosome. This binding, primarily mediated through regions II and V of the rRNA, occludes the peptide exit tunnel and inhibits bacterial protein synthesis. In addition, cethromycin is capable of binding to ribosomal intermediates during ribosome biogenesis, inhibiting the formation of functional 70S bacterial ribosomes. Due to the sequence and structural similarity of ribosomes between species, cethromycin displays broad-spectrum activity against diverse Gram-positive, Gram-negative, and atypical bacteria.

Extensive studies of cethromycin metabolism have not been conducted, although one study identified seven metabolites within feces of patients administered a single 150 mg oral dose. The major recovered products were unchanged cethromycin and an inactive N-desmethyl metabolite. It is likely that most of the metabolism occurs in the liver and is mediated, at least in part, by CYP3A4.

Cethromycin displays non-linear absorption kinetics. In healthy adults administered 150 mg cethromycin orally once daily for five doses, the calculated Cmax, Tmax, and AUC0-24 values were 0.181 ± 0.084 μg/ml, 2.01 ± 1.30 hrs, and 0.902 ± 0.469 μg\*h/ml, respectively. Similarly, the corresponding values for a 300 mg dose were 0.500 ± 0.168 μg/ml, 2.09 ± 0.03 hrs, and 3.067 ± 1.205 μg\*h/ml, respectively. In another study using a single oral dose of 150 mg cethromycin, the Cmax was 318 ± 161 ng/ml, the Tmax was 1.79 ± 0.50, the AUC0-24 was 1596 ± 876 ng\*h/ml, and the AUC0-∞ was 1662 ± 907 ng\*h/ml.