Objective: To investigate effect of compatibility of Ephedrae Herba-Cinnamomi Ramulus on pharmacokinetics of ephedrine in rats by microdialysis. Method: The suitable microdialysis sampleing technical conditions of ephedrine were developed by investigating the velocity

the concentration of ephedrine and other factors.Rat plasma samples were collected by microdialysis sampling technique

Rats were given ephedrine

Ephedrae Herba and herb pair of Ephedrae Herba-Cinnamomi Ramulus solutions.The concentration of ephedrine was determined by LC-MS at different times.Pharmacokinetic differences of three groups were compared by DAS 3.0 software. Result: The suitable conditions of microdialysis for ephedrine were the velocity of 1.5 μL·min-1

sample interval for 20 min and sample concentration within 0.1-3.0 mg·L-1.There were no difference of AUC in three groups.Compared with the ephedrine group

Tmaxand Cmax of the Ephedrae Herba-Cinnamomi Ramulus (3:2) group had no statistical significance;while their T1/2

MRT

CLZ/F and VZ/F had statistical significance.By comparing with the Ephedrae Herba group

Cmax of the Ephedrae Herba-Cinnamomi Ramulus (3:2) group had no statistical significance

but their Tmax

T1/2

MRT

CLZ/F and VZ/F had statistical significance. Conclusion: Compatibility of Ephedrae Herba-Cinnamomi Ramulus accelerates the metabolism of ephedrine

and it may be the reason why Ephedrae Herba is relatively safe when compatibility with Cinnamomi Ramulus.