Cethromycin

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.

Cethromycin is primarily excreted by the biliary route, with 87.2% of an initial dose recovered in feces and only 7.0% in urine. Unchanged cethromycin accounted for 35.7% of the radioactivity recovered in feces and an N-desmethyl metabolite for 39.8%; the remaining radioactivity was approximately evenly divided between three minor metabolites and a group of uncharacterized additional products.

Cethromycin given in five 150 mg oral doses had an apparent volume of distribution at the terminal elimination phase of 1433 ± 843 L, and an apparent steady-state volume of distribution of 1453 ± 997 L. The corresponding values for a 300 mg dose was 761 ± 293 L and 769 ± 272 L. Cethromycin is known to accumulate in the epithelial lining fluid and alveolar cells, as well as within polymorphonuclear leukocytes.

Cethromycin clearance in patients receiving a once-daily oral dose of 300 mg is reported to be approximately 63 L/h.