Example: After an iv administration of 1000 mg cefazoline urine samples were collected and the following data were obtained.
| Time (hr) |
R.Exc Rate (mg/hr) |
Time (hr) |
Plasma conc. (mg/ml) |
| 0-1 |
332 |
0.5 |
85.0 |
| 1-3 |
117 |
2.0 |
48.0 |
| 3-5 |
70.0 |
4.0 |
19.2 |
| 5-8 |
22.5 |
6.5 |
6.0 |
| 8-12 |
4.5 |
10.0 |
1.2 |
Calculate renal clearance of cefazoline.
The can be calculated from the renal excretion rate and the plasma concentration at the middle point of the urine collection interval:
| Time interval (hr) |
Renal Exc. rate (mg/hr) |
Plasma Conc (mg/ml) |
Renal clearance (L/hr) |
| 0-1 |
332 |
85.0 |
3.9 |
| 1-3 |
171 |
48.0 |
3.56 |
| 3-5 |
70.0 |
19.2 |
3.64 |
| 5-8 |
22.5 |
6.0 |
3.75 |
| 8-12 |
4.5 |
1.2 |
3.75 |
The can be calculated from the average of the renal clearance estimates calculated for all urine collections.
Also, a plot of the renal excretion rate versus the plasma concentration at the middle point of the urine collection interval (on a ) is a straight line with a slope equals to the .
The renal clearance is determined from the slope of the line.
Renal Clearance = 3.8 L/hr
