Endothelial cell compatibility of azithromycin and erythromycin

Phlebitis is a severe local adverse event related to the use of parenteral macrolides. In order to evaluate the effect of azithromycin and erythromycin on human venous endothelial cells, we set up an in vitro model. The intracellular levels of purine nucleotides, as adenosine 5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP) and guanosine 5′-triphosphate (GTP), were measured by means of high-performance liquid chromatography. Incubation of cells with 2 mg/mL azithromycin and erythromycin resulted in a rapid decline of intracellular ATP from 12.5 ± 0.9 nmol/million cells to 4.1 ± 0.3 and 2.6 ± 0.4 nmol/million cells, respectively, after 60 min. In addition, ADP was extensively depleted from 2.1 ± 0.17 nmol/million cells to 0.8 ± 0.09 and 0.8 ± 0.13 nmol/million cells after 60 min. After exposure of 0.5 mg/mL azithromycin and erythromycin, no significant decline of intracellular high-energy phosphate levels occurred after 20 and 60 min. Based on these results, solutions of azithromycin and erythromycin may not be well tolerated and may cause local adverse reactions even if diluted according to the manufacturer's recommendation.