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Abstract
Warfarin is an oral anticoagulant used in thrombo embolic disorders. Vitamin K is an essential co factor in the activation of clotting factors synthesized in liver (II , VII, IX, X). Warfarin acts by inhibiting the regeneration of active form of Vitamin K. Green tea, which is actively promoted as a natural remedy for numerous cardiovascular disorders contains a significant quantity of Vitamin K [2]. An effort was made in this study to explore the potential pharmacodynamic interaction between green tea and warfarin. The objective of the study was to asses the effect of green tea on the pharmacodynamics of a single oral dose of warfarin in healthy volunteers. 15 healthy male volunteers in the age group of 18 - 40 years were selected and given 20mg warfarin orally on Day 1 of Phase I. PT and INR were measured for 7 days. After a washout period of 7 days, green tea was given thrice daily (6 gm / day) for 10 days. On the 4th day of green tea administration, 20mg warfarin was given in Phase II and PT and INR were measured for 7 days. Day-wise and Phase-wise means were calculated, along with other pharmacodynamic parameters like INR^sub max^, PT^sub max^, PT^sub AUC^, INR^sub AUC^ and time to reach PT^sub max^ and INR^sub max^. Two tailed t test was used to analyse the differences. There was a statistically significant decrease in the mean INR(p=0.042) and PT (p=0.021) in the treatment phase (warfarin + green tea) when compared with the control phase (warfarin alone).When the mean INR and PT for each day was analysed separately, this difference was statistically significant only on Days 5 and 6. As the antagonism of warfarin by Vitamin K is competitive in nature, this finding assumes significance and highlights a need for caution when green tea is consumed by patients on warfarin.
Keywords: Thromboembolic disorders, Warfarin, Vitamin K, Green Tea, Prothrombin Time ( PT), International normalized ratio (INR)
Introduction
The oral anticoagulant warfarin is often prescribed long term in patients with valvular heart disease, atrial fibrillation or deep vein thrombosis. It has a narrow therapeutic index, innumerable drug interactions and shows high inter and intra patient variability.
Green tea (Camellia sinensis) is made from unfermented leaves...