Time (hr) | Cp (mg/L) |
2 | 0.04 |
3 | 0.028 |
4 | 0.019 |
6 | 0.009 |
8 | 0.005 |
10 | 0.002 |
12 | 0.001 |
Estimate kel, t_{1/2}, V, and Cl.
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Equation 15.3.1 Drug concentration, Cp, after an IV infusion
The table above provides a set of data for you to analyze. Using these data you should be able to estimate the elimination rate constant (kel), the elimination half-life (t_{1/2}), the apparent volume of distribution (V) and the total body clearance (CL) for the drug. First graph the data on semi-log graph paper and put a straight line thorugh the data. A best fit line. Don't try to put the line through any particular point but through all the data. The best fit line may not go through any of the points. A clear ruler helps. Then you can see the points above and below the line to get a good balance. Draw the line. Estimate the intercept on the left and right extreme of the line. Use these extreme points from the line to estimate kel from the -slope (using the natural log, ln, version) as:
Now you can either pick one of the concentrations (from the line) and substitute into the equation above to find V. Alternately you could extrapolate the 'best-fit' line back to the end of the infusion, not the y-axis (time zero).
Equation 15.3.2 Cp^{D} at the end of the infusion period, T
With an estimate of Cp^{D} it is possible to rearrange Equation 15.3.2 and calculate V, the apparent volume of distribution:
Equation 15.3.3 V estimated from Cp^{D} data