血浆半衰期

Determination of half life in plasma of sodium salicylate [sə'lɪsɪlət]【Principle】

Sodium salicylate and ferric trichloride [traɪ'klɔiraɪd]can form purple compound whose absorbance is in direct proportion to the concentration of sodium salicylate at wavelength 520 nm. According to the above principle, the concentration-time curve can be drawn by collecting the blood sample from the experimented rabbit at different time point after intravenous administration of sodium salicylate, as well as detecting the concentration of sodium salicylate by spectrophotometry [,spektrəufəu'tɔmitri]. The pharmacokinetic parameters as first-order elimination kinetics can be worked out.

T1/2(half-life of drug): is that drug to fall to half of its original value.

First order elimination kinetics: the half-life of the drug eliminated by first order kinetics is a constant.

acid environment: 酸性环境

nanometer ['neɪnəmi:tə]: nm

【Purpose】

1.The method of determination of half life in plasma of drug----

spectrophotometry

2.How to use spectrophotometry

1)Preheat the machine for 20 minutes: Turn on the power switch.

2)Turn the wavelength 520 nm (left window)

3)zero-setting (1) open cover 指针（ Pointer， Cursor， hand，needle）Adjust knob

among, the pointer to 0.

4)100%-setting: close the cover, adjust the right knob, the pointer to the 100.

5)Then test the sample.

【Materials】

1. Animals: rabbits with weight about 3 kg.

2. Drugs: 10% sodium salicylate, 10% trichloroacetic acid，10% ferric trichloride，distilled water.

3. Instruments: spectrophotometer，centrifuge，calculator, rabbit operating table, test tube rack, beaker (50mL), syringe (2mL), pipettes (5mL, 1mL, 0.5mL), test tube (10mL).

【Method】

1. Set up 3 test tubes labeled No.1～3. Pipette 10% trichloroacetic acid 3.5mL into each tube.

2. Take 1 rabbit, weigh and fix it on its back on the operating table. With the syringe moistened with 1% heparin in advance, take blood 2mL from heart directly. The blood should be put into No.1 tubes equally. Take No.1 as zero-setting tube. Then shake them and let them stand.

3. Slowly inject 10% sodium salicylate 2mL•kg-1 (200mg•kg-1) into the brink vein of ear. At 5min and 20 min after administration, take 1mL of blood from the heart each time and put the sample in No.2 (Test tube 1) and No.3 (Test tube 2) respectively. Shake them and let them stand.

4. Then centrifuge all three tubes for 5min with 2500r/min rotation speed at same time.

The key of this step is balancing----same volume

5. Respectively pipette the clear supernatant 3mL from each tube into another three tubes labeled same numbers with those of former tubes. Put 10% ferric trichloride 0.5mL into each tube and shake them. Determine the absorbance of solution in No.2～3 tubes at wavelength 520nm with spectrophotometer, setting zero absorbance with No.1 solution.

The color of No.2 is darker than the No.3

【Results】

1.

Detrmination of t l/2

(1) Calculation Method: According to the absorbance at 5min and 35min (No.2 and No.3) and the interval of twice taking blood sample △t(min), calculate t l/2 with the following formula.

t l/2=

0.301

(lg Ab2-lg Ab3)/△t