Objective: To optimize formula of Bixie Fenqing rectal gel and compare its pharmacokinetics after oral and rectal administration in rabbits. Method: Taking appearance

uniformity

viscosity and pH value as indexes

the amount of carbomer 940

dosage ratio of glycerol and propylene glycol

the amount of NaOH were independent variables

uniform design-response surface methodology was adopted to optimize formulation of the rectal gel.Concentration of glycyrrhetic acid in the plasma was detected by HPLC after oral and rectal administration

3P97 software was employed to calculate the pharmacokinetic parameters and evaluate the pharmacokinetic behavior. Result: The best formula was as following: 1.5% of carbomer 940

8% of glycerol and 2% of propylene glycol

1% of NaOH

0.03% of ethyl p-hydroxybenzoate.The main pharmacokinetic parameters after rectal administration were as follows: Cmax of (35.144 7±5.272 4) mg·L-1

Tmax of (27.114 6±13.358 7) min

AUC0-6 h of (5 125.468 5±368.745 9) mg·min·L-1. Conclusion: This established mathematical model has good prediction

the appearance of Bixie Fenqing rectal gel is exquisite

its viscosity is suitable

its main components are absorbed rapidly with high bioavailability.