Example : An antiarrhythmic drug is completely metabolized by the liver. Its hepatic extraction ratio is 0.89 in a patient with congestive heart failure who has liver blood flow of 1.22 L/min. Calculate the hepatic clearance of this drug in this patient. The patient started taking an isotropic drug which increased the liver blood flow to 1.62 L/min. Calculate the hepatic clearance of this drug after the increase in hepatic blood flow.

Q (L/min)

The increase in liver blood
flow decreases the hepatic
extraction ratio since
CLint does not change.

E =

CLint

Q + CLint

Answer:

a- CLH before the inotropic drug:

CLH = 1.22 L/min x 0.89 = 1.09 L/min

b- CLH after the inotropic drug:

1.22 L/min x 0.89

1 - 0.89
=

1.62 L/min x Enew

1 - Enew
E = 0.86
CLH = 1.62 L/min x 0.86 = 1.39 L/min