Lecture 3 - Absorption and Half-life

Question 1

Extent?

Answer 1

Fraction absorbed (f) into portal vein from gut x 1 - first pass extraction (ER)

Question 2

First pass extraction?

Answer 2

drug removed while passing through the liver - subject to organ clearance and blood flow

Question 3

Different input processes and example?

Answer 3

Bolus (intra-venous injection), zero order (constant rate IV infusion), first order (intra-muscular injection)

Question 4

Controls of zero order rate?

Answer 4

physiological - stamoch emptying relatively constant; pharmaceutical control - slow release formulation

Question 5

Zero-order input timeline?

Answer 5

blood conc. rise to input conc. after first hour, followed by sloped decline; elimination is prop. to blood conc. only, as input is constant

Question 6

First order absorption rate?

Answer 6

intestinal absorption (Ka); diffusion limited, half life measure, approx. complete @ 4 half lives

Question 7

First-order input timeline?

Answer 7

blood conc. exponentialy increase then slopes, rate abs. exponentially decreases to asymptote, elimination results in curved increased for first hour then sloped decrease

Question 8

Applications of absorption graphs?

Answer 8

IV/oral conversion, time to peak conc./effect, substitute of generic medicines

Question 9

Accumulation of drug through repeated exposure?

Answer 9

@ 4 half lives (after 3), steady state is accomplished (>90%), meaning that the concentration of drugs increases negligibly at repeated doses