Question

Drug X is a new oral cephalosporin. the package insert states the following: feu=0, F=9,fb=0.6, CLtotal=0.21L/h/kg, po dose=3.6 mg/kg q6h, Qp=0.8L/h/kg

what is the hepatic extraction ratio of drug x?

is drug x restrictive or non-restrictively cleared?

will enzyme induction cause a significant interaction for drug x?

what is the Cssaverage of drug x in a 70kg patient at the po dose given above?

Answer 1

The hepatic extraction ratio is the ratio of the hepatic clearance of a drug to the hepatic blood flow. Hepatic extraction ratio greater than 0.7 is termed high, ranging between 0.3 to 0.7 is intermediate and below 0.3 is low.

Hepatic extraction ratio = hepatic clearance/hepatic blood flow

Hepatic extraction ratio = 0.21/0.8 = 0.26

The drug have low extraction ratio. This means that the drug is not efficiently cleared by the liver and incompletely extracted from hepatic blood. The extraction is said to be restrictive.

Yes enzyme induction cause a significant interaction for drug x.

Css average =( F x drug dose/time) / Cl total