PHARM/PCS V5 · Procedure 30
Pharmacokinetics V: Renal Clearance
Compute renal clearance two ways: from total urinary excretion over AUC, and from excretion rate against plasma concentration.
What it computes
Computes renal clearance of a drug by two methods. Method A divides the total amount of unchanged drug excreted in urine by the area under the plasma-concentration curve. Method B takes clearance as the slope of a regression, through the origin, of urinary excretion rate against plasma concentration.
Inputs and outputs
You provide
- Method A: time, plasma concentration, and amount of unchanged drug in urine at each collection
- Method B: collection end time, plasma concentration at the midpoint, and amount excreted in the interval
PHARM/PCS reports
- Renal clearance by Method A, total amount excreted over AUC
- Renal clearance by Method B, the slope of excretion rate against plasma concentration
- For Method A, the plasma concentration curve with the AUC shaded; for Method B, excretion rate against plasma concentration, where the slope is the clearance
When to use it
When you have paired urine and plasma data and want renal clearance: Method A when you can measure total excretion and AUC, Method B when you have excretion-rate/concentration pairs. It sits within the PK series and shares tools with Procedures 25 (AUC) and 4 (through-origin regression).
Reading the results
The two methods should roughly agree; a large gap points to incomplete urine collection (Method A's usual failure) or a clearance that isn't constant across the range (which bends Method B's line). Complete, accurately timed urine collection is the make-or-break input for both.
Two methods as a cross-check
Having both methods in one procedure gives you a built-in check. When they disagree, look first at urine collection and at whether clearance stays constant across the concentration range. Both methods reproduce the 1986 results exactly.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.