Danggui (Angelica sinensis) affects the pharmacodynamics but not the pharmacokinetics of warfarin in rabbits

Danggui is a popular traditional Chinese medicinal (TCM) herb which is easily obtained by the public. The effects of Danggui on the pharmacokinetics and pharmacodynamics of warfarin were studied in rabbits. Single subcutaneous doses (2 mg/kg) of warfarin were administered to 6 rabbits with or without 3 days treatment with oral Danggui extracts (2 g/kg twice daily). Plasma warfarin concentrations were measured by high performance liquid chromatography (HPLC) for 72 h after each of the two warfarin doses. The prothrombin time (PT) was measured daily for 3 days both during the Danggui treatment period and after warfarin doses. Danggui treatment did not affect PT on its own, but significantly lowered PT values 3 days after co-treatment with single dose warfarin. No significant variations in the single dose pharmacokinetic parameters of warfarin were observed after Danggui treatment. A separate group of 6 rabbits were given daily subcutaneous doses of warfarin (0.6 mg/kg) to achieve steady state level, followed by 3 day treatment with oral Danggui extract (2 g/kg twice daily). The slight increase in PT was not significant and two rabbits died after day 7 of the treatment period. However, there was no significant difference in steady state concentrations of warfarin after the Danggui treatment. Results indicate that precautionary advice should be given to patients who self-medicate with Danggui or other TCM products while on chronic treatment with warfarin.