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  • Title: Inhibition of P-glycoprotein-mediated efflux of digoxin and its metabolites by macrolide antibiotics.
    Author: Hughes J, Crowe A.
    Journal: J Pharmacol Sci; 2010; 113(4):315-24. PubMed ID: 20724802.
    Abstract:
    This study was conducted to determine the rate of P-glycoprotein (P-gp)-mediated efflux of digoxin analogues and metabolites and to assess the effects of macrolide antibiotics on this efflux. Bidirectional transport studies were conducted using our Caco-2 sub clone with high P-gp expression (CLEFF9). HPLC methods were employed to measure drug transport. All digoxin metabolites were P-gp substrates, although digoxin had the greatest efflux ratio. Erythromycin had no effect on the transport of digoxin, maintaining a basolateral to apical efflux ratio of 14.8, although it did reduce the efflux ratio of dihydrodigoxin and digoxigenin by 34% and 43%, respectively. Azithromycin also had little effect on the transport of digoxin or any of its metabolites. In contrast, clarithromycin and roxithromycin almost eliminated basolateral targeted efflux. Using paclitaxel as a known P-gp substrate, erythromycin demonstrated only partial P-gp inhibitory capacity, maintaining an efflux ratio over 100. In contrast, clarithromycin and roxithromycin were 10-fold greater P-gp inhibitors. Clarithromycin and roxithromycin are likely to exhibit drug interactions with digoxin via inhibition of efflux mechanisms. Azithromycin appears to have little influence on P-gp-mediated digoxin absorption or excretion and would be the safest macrolide to use concurrently with oral digoxin.
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