Factors Affecting the Urinary
Excretion of Drugs (Cont'd)

d- Both CLT and CLR

Examine the renal excretion rate after administration of the same dose of drugs that have different CLR, and CLT , but the ratio (CLR/CLT) is constant.

Parameters
Dose (mg) CLΤ(L/hr) CLR(L/hr)
100 2 1
CLR (L/hr)

The rate of decline of the renal excretion rate versus time plot is dependent on CLT. Because the ratio of CLR/CLT is constant the fraction of dose excreted in urine will always be constant.

Parameters
Dose (mg) CLΤ(L/hr) CLR(L/hr)
100 2 1
CLR (L/hr)

The fraction of dose excreted unchanged in urine is constant because the ratio of CLR/CLT is constant. Because the dose is constant, the same cumulative amount is excreted in urine.

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