Abstract: Objective:To establish a drug concentration in plasma determination method based on fluorescence polarization immunoassay (FPIA),and to explore the feasibility of this method in monitoring the concentrations of three small molecular drugs including gentamycin,digoxin and sodium valproate in plasma of the mice. Methods:The standard samples of gentamycin,digoxin,and sodium valproate were selected. The limits and linear ranges of drugs were measured with fluorescence polarization(FP) non-linear fitting method. Three standard groups with low,medium,and high concentrations of drug were selected during liver range,and the accuracy,inter-day precisions and serum anti-interference abilities of the mice were detected.Total 30 KM mice were divided into gentamycin group (5 μg·g^-1,intramuscular injection),digoxin group(20 ng·g^-1,gavage) and sodium valproate group(15 μg·g^-1,gavage); the blood drug concentrations of the mice were measured at 1,3,6,12 and 24 h time points after administration. Results:For all three drugs detected,the detection limits detected by FPIA were lower than 50 μg·L^-1),the linear ranges were broad (more than 10 times of detection limit),the accuracy (ER) was lower than <5% and the inter-day precisions were higher (CV<5% in medium and high concentration groups).The mouse serum showed no affection to FPIA detection qualities for gentamycin and digoxin,while high concentration of serum negatively affected the detection quality for sodium valproate (ER=-12.84% in 50% serum group).After administration,gentamycin reached the peak blood concentration at 1 h with half-life period of 3 h,digoxin reached the peak blood concentration at 1 h with half-life period of >24 h,and sodium valproate reached the peak blood concentration at 3 h with half-life period of 6-12 h. Conclusion: FPIA for small molecular drug concentration in plasma of the mice has the advantages of small sample size,high accuracy,simple preprocessing,high throughput detection and rapid test,which can be applied in determination in pharmacological,pharmaceutical and clinical research.

Key words: drug plasma concentration, sodium valproate, gentamycin, fluorescence polarization immunoassay, digoxin