Estimate Renal Clearance from Urine versus Time Data
IV Bolus  Linear One Compartment
Using the Rate of Excretion versus Cp Plot
with suggestions from Sukyung Woo, PhD
A dose of 250 mg was administered intravenously to a healthy volunteer. Total urine samples were collected after 2, 4, 6, 8, 10, 12, 18 and 24 hours. Samples were well mixed and analyzed for drug concentration. The volume of each sample was also recorded. During the study, plasma sample were collected at the midpoint (Tmid) of each collection period. The collected data are shown in the table below.
Urine Data 
Plasma Data 
Time (hr)

Urine Volume (ml)

Cu (mg/ml)

T_{mid} (hr)

Cp (mg/L)

2 
135 
0.234 
1 
8.66 
4 
126 
0.154 
3 
5.31 
6 
142 
0.084 
5 
3.27 
8 
130 
0.057 
7 
2.01 
10 
145 
0.031 
9 
1.24 
12 
137 
0.02 
11 
0.762 
18 
431 
0.008 
15 
0.288 
24 
369 
0.002 
21 
0.0669 
The table above provides a set of data for you to analyze. Using the plasma data, plot the Cptime data on a semilog graph and estimate the overall elimination rate constant, volume of distribution, and total clearance for the drug. Using the urine data, first calculate the amount of unchanged drug excreted during each time interval and then the cumulative amount excreted upto that time point, U. Calculate the rate of excretion during each interval. A plot of the rate of excretion against the corresponding plasma concentration in a linear graph yields a straight line with a slope equal to renal clearance.
Your objective is to estimate kel, total CL, fe, CLr, CLm and ke.
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Some Equations:
Equation 12.3.1 Total Clearance
Equation 12.3.2 Renal Clearance
Equation 12.3.3 Fraction Excreted Unchanged
Equation 12.3.4 Renal Clearance and Excretion Rate Constant
Equation 12.3.5 Metabolic Clearance
Equation 12.3.6 Metabolic Rate Constant
Last update: Sun 21 Apr 2019 08:29:30 pm
Copyright © 200219 David Bourne (david@boomer.org)