Effect of purple grape juice on the pharmacokinetics of digoxin: Results of a food-drug interaction study

Digoxin is a glycosidic, cardiotonic plant extract with a narrow therapeutic window. The purpose of the study was to investigate the effects of purple grape juice on the pharmacokinetics of digoxin in rats.A randomized, controlled, single- and multiple-dose study was conducted to evaluate the pharmacokinetic profiles of orally and intravenously administered digoxin. The plasma concentration of digoxin was determined by radioimmunoassay using a gamma counter, and a Caco-2 cell transport model was used to investigate the potential mechanism by which purple grape juice affects the pharmacokinetics of digoxin.The results show that multiple-dose purple grape juice caused a remarkable increase in the AUC, Cmax, and Ka of orally administered digoxin (p < 0.05); only a single dose increased the digoxin AUC0-∞ by 72.80% (p < 0.05). Other parameters were not significantly affected. The study of intravenously administered digoxin found no significant difference in the pharmacokinetic characteristics of the two dosing groups (p > 0.05). The Caco-2 transwell experiments indicated that both the pure purple grape juice and its ethyl acetate extract significantly inhibited digoxin basolateral-to-apical (B→A) transport at concentrations of 10%, 30%, and 50% with dose dependency. These results confirmed that the improvement in bioavailability of digoxin resulted from the inhibition of P-gp by purple grape juice at the level of the gastrointestinal wall.Purple grape juice can increase the bioavailability of orally administered digoxin, especially with multiple doses. This information suggests that co-administration of oral digoxin and purple grape juice may require a dose adjustment. .