Drug Interactions between digoxin and green tea

MONITOR: Coadministration with green tea may decrease the plasma concentrations of digoxin. The mechanism of interaction has not been established, but may involve induction of P-glycoprotein (P-gp)-mediated efflux of digoxin in the intestine by one or more of the catechins in green tea, or inhibition of one or more transporters involved in the intestinal uptake of digoxin that have yet to be identified. In a study consisting of 16 healthy volunteers, administration of a single 0.5 mg dose of digoxin following pretreatment with green tea extract for 13 days decreased digoxin peak plasma concentration (Cmax) and systemic exposure (AUC) by 26% and 33%, respectively, compared to administration of digoxin alone. The green tea used in the study was a commercially available 630 mg formulation of green tea extract containing 300 mg of catechins. It is not known whether, and to what extent, the data from this study may be applicable to other preparations and products of green tea, since the compositions, amounts, and bioavailabilities of catechins may vary substantially.

MANAGEMENT: Patients should consult a healthcare provider before taking any herbal or alternative medicine. If green tea products are consumed regularly, digoxin levels may need to be checked more frequently and the dosage adjusted accordingly. Patients should be advised to notify their physician if they experience a worsening of their heart symptoms. Due to differences in phytochemical content and potency of commercial herbal products in general, the pharmacokinetic effects of green tea may vary depending on the specific preparation.