Absorption And Distribution Interactions Between Warfarin And Aspirin

Warfarin and aspirin are the first-line drugs for anticoagulant and antiplatelet therapy, respectively. A certain percentage of patients have both the risks of arterial thrombosis and intravenous or intracardiac thrombosis in clinic. Only one type of thrombosis risk is satisfactorily suppressed by anticoagulation or antiplatelet therapy. Thus, warfarin and aspirin combination therapy are often required. Combined warfarin and low-dose aspirin are very common abroad, and is currently used in about 1 million patients in North America. In addition, the safety of combined therapy as it relates to bleeding risk should also be considered. Despite wide use, there is still a lack of evidence for the combination. Evaluation of its efficacy and safety in academic and clinical circles remains a matter of great controversy. The recommendations were not clearly stated in various clinical practice guidelines except for mechanical heart valves. Doctors also often confused that when and how to conduct the combined warfarin-aspirin therapy in clinical practice. There is only limited evidence for the benefit and harm of the combination from some randomized trials. However, the literature of related preclinical animal study and pharmacokinetic study of the combination therapy is rare. The specific mechanism of action is unknown yet.The aim of the present study is to explore the interactions during absorption and distribution between warfarin and aspirin in situ and in vivo, which can provide a basisfor the rational combination therapy in clinical practice.This study was divided into three parts:1. Study of drug interaction between aspirin and warfarin in situ intestinal absorption modelThe rat single-pass intestinal perfusion model was performed to investigate the intestinal absorption of drugs, and the gravimetry was used to correct the perfusion volume. The concentrations of warfarin enantiomers and aspirin in the perfusion samples were determined by HPLC. The absorption rate constants(Ka) and apparent permeability coefficients(Papp) were calculated to study the differences of absorption of warfarin enantiomers and aspirin among the aspirin group, warfarin group, combination group, aspirin induced group and warfarin induced group. There were no significant differences in R-warfarin and S-warfarin absorption between warfarin group and warfarin combined with aspirin group(P > 0.05). The Ka and Papp of warfarin enantiomers in duodenum and jejunum were significantly decreased in aspirin induced group compared with that in warfarin group(P<0.05). No significant differences in aspirin absorption in the four intestinal segments were observed between aspirin group and aspirin combined with warfarin group or warfarin induced group(P>0.05). Long term use of aspirin can obviously decrease the absorption of R-and S-warfarin in duodenum and jejunum, and there was no difference between the two enantiomers. The absorption of aspirin was not statistically affected by adding warfarin.2. Evaluation of drug interaction between aspirin and warfarin in a MDCK modelThe MDCK cell membrane model was performed. The safety concentrations of aspirin and warfarin in MDCK cells were determined by MTT assay. The apparent permeability coefficients(Papp)were calculated to study the differences of absorption and transport of warfarin enantiomers and aspirin between the aspirin alone group, warfarin alone group and the combination group. The concentrations of warfarin enantiomers and aspirin were measured by HPLC. High concentrations of aspirin(200and 300mg/L) can obviously decrease the amount of R- and S- warfarin in apical-basal direction at 120 min or 90 min, significantly decrease the Papp(A-B) and a trend to a decrease of the Papp(B-A) was observed. The amount and Papp of aspirin was not statistically affected by adding warfarin. Prolonged use of high concentrations of aspirin can limit the absorption of R- and S-warfarin, which may be related to aspirin’s ability to induce MDR1 in intestinal epithelial cells. It was suggested that warfarin did not affect the absorption of aspirin.3. Competitive binding of warfarin and aspirin to human serum albumin in multidrug therapy: A spectroscopic studyThe interaction of warfarin and aspirin on HSA was studied by fluorescence spectra under simulated physiological. The quenching constants were calculated with the Stern-Volmer equation, and the binding constant(KA) and the number of binding site(n) were obtained.Warfarin and aspirin could cause the static quenching of HSA endogenous fluorescence due to forming compound. At 310 K, KA of WAR-HSA and WAR-ASA-HSA was 3.50×104 and 1.20×104 L·mol-1, the ratio was 0.34; KA of ASA-HSA and ASA-WAR-HSA was 2.37×103 and1.14×103 L·mol-1, the ratio was 0.48. Two-coexisting warfarin and aspirin may lead to the interaction. The presence of one drug would reduce the binding constant and stability of the other drug with HSA, which induces the concentration of free drug increasing and the efficacy of the drugs could be enhanced.