Determination of Renal Drug Clearance: Graphical and Midpoint Methods

Renal clearance can be determined using graphical and midpoint methods.

In the graphical method, clearance can be calculated and obtained by plotting the rate of drug excretion in urine and plasma drug concentration.

Rapidly excreted drugs have a larger excretion rate with a steeper slope and greater clearance.

In contrast, slowly excreted drugs exhibit a smaller slope.

Rearranging and integrating the clearance equation yields cumulative drug excreted in the urine. Plotting the graph determines renal clearance from the slope.

A disadvantage of this method is that if a data point is missing data, it is challenging to obtain the cumulative drug amount excreted in urine.

Alternatively, renal clearance can be calculated using the midpoint method, where plasma concentration at the midpoint of the collection interval is used.

Although this method is less robust, it is clinically used when only a limited number of plasma drug concentrations can be collected and measured.