Calculation of the clearance

(From the drug excretion rate data)

Determination of the overall drug excretion rate from the body is not easy. The renal drug excretion rate can be determined easily by measuring the amount of the drug excreted in urine over a certain period of time. This can be used to determine the renal clearance.

a- The amount of the drug excreted in urine is determined over a short time interval (1 - 2 hr).

b- Calculate the renal excretion rate (amount of drug excreted/time interval).

c-Obtain the average plasma conc during the urine collection interval (plasma concentration at the middle of the urine collection interval).

Drug excretion rate

Cp at the same time = Renal Clearance

The renal clearance is equal to the total body clearance only when the drug is completely excreted unchanged in urine.

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