Pharmacokinetics

Question 1

define pharmacokinetics

Answer 1

what the body does to the drug

Question 2

what are the 4 main components of pharmacokinetics ?

Answer 2

Absorption , Distribution , metabolism nd eliminations

Question 3

Define bioavailability

Answer 3

the absorption of a drug into a compartment where it can be used . IV = 100%

Question 4

what is first pass metabolism ?

Answer 4

metabolism before reaching systemic circulation e.g. gut lumen and brush border

Question 5

what can affect distribution?

Answer 5

Blood supply to tissue 
endothelial structure 
lipo vs hydro philicity
protein binding 
Vd

Question 6

what effect does protein binding have on drug distribution ?

Answer 6

only free drug will cause a response or be eliminated

another drug can displace protein binding leading to free 1 st drug

Question 7

What is Vd and how is it calculated ?

what does Vd tell you ?

Answer 7

the amount of fluid needed to contain the dose at the same concentration as in plasma
dose/Drug in plasmsa
smaller Vd = drug confined to plasma + EX(cell)
larger = throughout tissue as well

Question 8

what is relationship of T1/2 to Vd? What is T1/2?

what is relationship of . T1/2 to clearance?

Answer 8

proportional . time in which conc of drug decrease by 1/2 in the plasma .
inversely proportional

Question 9

what is the main enzyme of phase 1 metabolism and where does it occur and what does it do the drug ?

Answer 9

CYP450 , Liver and makes lipophilic metabolites

Question 10

what else can affect phase 1 metabolism ?

Answer 10

compounds affecting CYP450 , Age, hepatic disease, alcohol and cigarette, genetics of CYP450

Question 11

What are routes of elimination of a drug ?

Answer 11

Kindeys , pulomonary , biliary, faeces , saliva and breast milk

Question 12

What effects in a drug that is partially water soluble in terms of elimination ?

Answer 12

GFR and protein binding
competition for transporters
lipid solubility, Ph and flow rate

Question 13

what is clearance and what is a good estimate of it ?

Answer 13

rate of Clearance from all routes - metabolism + excretion . look at GFR. if GFR halved then T1/2 doubled

Question 14

what is the difference between first order and zero order kinetics ?

Answer 14

rate of elimination is proportional to drug conc

zero order = rate of elimination is constant due to receptor saturation

Question 15

when might you see zero order kinetics ? why is it a problem

Answer 15

enzyme saturation of Ethanol at high doses leading to rapid increase in plasma conc so T1/2 is not calculable

Question 16

how to work out loading dose ? what about maintenance dose?

Answer 16

LD = (Vd*weight) * CpSS / Bioavilabilty 
MD = Clearance * CSS/Bio

Question 17

How can you work out T1/2 from a graph?

Answer 17

if graph has log(CP) against time . The slope gives you k = CL/Vd

Question 18

what can affect our calcuations of Loading dose etc.?

Answer 18

multiple compartments in the body = multiple rate constants, Vd different