Simultaneous determination and pharmacokinetics of protein unbound aspirin and salicylic acid in rat blood and brain by microdialysis: an application to herbal-drug interaction.

Aspirin is commonly used for the prevention of myocardial infarction and ischemic stroke; whereas the Chinese people employ the bu-yang-huan-wu-tang (BYHWT) as a routine herbal formulation for the treatment and prevention of transient ischemic stroke. The current study develops a microdialysis technique coupled to a validated liquid chromatography system to measure free-form aspirin and salicylic acid for herbal-drug interaction in rat blood and brain. The intra- and inter-day precisions in biological dialysates were within 0.1-9.4% in the concentration ranges of 0.1-50 μg/mL and the accuracies ranged from -4.7 to 6.1%. The pharmacokinetic data demonstrate that the area under the concentration time curve (AUC) of the aspirin was 2031 ± 266 min μg/mL after aspirin administration (100mg/kg, i.v.). The AUC of salicylic acid was 12660 ± 1799 min μg/mL, which suggests that aspirin is quickly hydrolyzed to salicylic acid in blood and the metabolite can also be detected within 15 min in brain dialysate. The herbal-drug pharmacokinetic interaction showed no significant effect in blood and brain. The results of pharmacodynamics for the bleeding time suggested that there were no significant differences between the aspirin alone group and the BYHWT pretreated group. However, the bleeding time has been prolonged when compared aspirin alone or the group pretreated with BYHWT to the blank control. The conclusion provides practical information for clinical practice for the herbal formulation BYHWT and aspirin used concurrently.