The first-pass effect presystemic clearance

The fraction, f of orally administered dmg that successfully passes through gut lumen and gut 

Equation 7.5 shows that the overall extent of bioavailability is the product of two factors reflecting the two steps involved in an orally administered drug reaching the systemic circulation first, traversing the gastrointestinal membrane and, second, surviving the first-pass effect in the liver. 

example, let us assume that the orally administered dose of a dmg is 100 mg the fraction absorbed into the portal circulation is 0.9 and the fraction that survives the first-pass effect is 0.9. Therefore, = 0.9 x 0.9 = 0.81 (or 

In this example, therefore, 81 mg out of 100 mg of the administered dose will reach the general circulation and will be reflected in the (AUC)q and in the amount of drug excreted in urine (XJ . 

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