1) To investigation a first-order process, simulating plasma elimination and urine excretion after an IV. bolus dose administration.
BACKGROUND:
By an arrangement of beakers and a constant head water reservoir, it is possible to simulate plasma concentrations and drug amounts in urine after IV. bolus administration. The constant flow of water through the system, causes a first order dilution of the marker, potassium permanganate. You will sample the marker concentrations periodically and analyze the data using the pharmacokinetic methods appropriate to measure the parameters of the system.
METHOD:
Identify the plasma and urine components to the apparatus. Make sure that the water reservoir is full. Turn on the stirrer in the plasma beaker and adjust for gentle mixing. Establish a flow rate of 20 ml/min. Anywhere from 15 to 25 ml/min is OK.
You will be collecting plasma samples at 2.5, 7.5, 12.5, 17.5, 22.5, 27.5, 32.5, 37.5, 45, and 55 minutes and urine samples at 5, 10, 15, 20, 25, 30,35, 40,50, and 60 minutes after the dose. Arrange and label test-tubes to accommodate the samples.
'Inject' the plasma beaker with the 'dose' of potassium permanganate (15 drops of saturated solution), place an empty beaker in position to collect the urine sample. Use distilled water as the blank. The 5 ml sample can be obtained easily by using a Pasteur pipette with a 2 ml bulb. Take 3 full pipettes full, its quicker and easier. You don't need to know this volume accurately, just the concentration. The dose injected can be determined by taking the same volume as injected into the beaker and diluting it to 250 ml and measuring the absorbance. A dose of about 15 drops (saturated potassium permanganate solution) should be considered to equal 250 mg. Thus the absorbance measured is that for a 1 mg/ml solution.
Calibration of the Turner 330 model spectrophotometer
Plasma samples. Collect the 5 ml sample at the times designated quickly by pipette. Don't rinse the pipette between samples.
Urine sample. At each time point for urine collection, replace the beaker with an empty beaker. Measure the volume collected, mix the contents of the beaker to obtain a uniform solution, and take a 5 ml sample for analysis.
Each sample will be analyzed spectrophotometrically at 540 nm. Early samples may need to be diluted to give absorbance readings below 1. Remember to apply this dilution factor in your analysis of the results.
WRITE-UP:
Describe the apparatus, the working differential, and working integrated equation
Data analysis
Plot Cp versus time on semi-log graph paper. Calculate kel from the slope, calculate t(1/2).
Knowing Cp(0) and dose, calculate the apparent volume of distribution, V. Plot U versus time on linear graph paper, indicate U(infinity). Does the total amount collected at 60 minutes approximate U(infinity)? Does U(infinity) = DOSE? Plot Rate of excretion versus time on semi- log graph paper and calculate kel. Construct a 'clearance' plot by plotting the rate of excretion versus Cp(at the midpoint of the urine collection time). Measure the clearance as the slope of this line[1]. [How does this compare with the flow rate set experimentally?]
Data Sheet for the Model: P ------> U
Dose = 250 mg : Absorbance of a 1 mg/ml solution =
| Time (min) | Dilution Factor | Absorbance | Concentration |
| 2.5 | |||
| 7.5 | |||
| 12.5 | |||
| 17.5 | |||
| 22.5 | |||
| 27.5 | |||
| 32.5 | |||
| 37.5 | |||
| 45 | |||
| 55 |
| Interval | t at end | Absorbance | Conc in Urine | V of Urine |  U
| U | t
| U / t
| t midpoint | Cp at midpoint |
| - | 0 | 0 | ||||||||
| 0 - 5 | 5 | 5 | 2.5 | |||||||
| 5 - 10 | 10 | 5 | 7.5 | |||||||
| 10 - 15 | 15 | |||||||||
| 15 - 20 | 20 | |||||||||
| 20 - 25 | 25 | |||||||||
| 25 - 30 | 30 | |||||||||
| 30 - 35 | 35 | |||||||||
| 35 - 40 | 40 | |||||||||
| 40 - 50 | 50 | |||||||||
| 50 - 60 | 60 | 10 | 55 |
Copyright 2001 David W.A. Bourne