Pharmacokinetics Flashcards
(42 cards)
4 main parts to pharmacokinetics
Absorption, distribution, metabolism, elimination
absorption
the proportion of an administered drug that reaches systemic circulation- bioavailability
what affect absorption (3)
GI, Route of admin and lipophilicity
GI AND ABSORPTION
contains proteases which may breakdown the drug, monoclonal antibodies- breakdown and recombinant proteins
- first pass metabolism - since hepatic vein takes blood from the stomach to the kidney
route of administration and absorption
IV= direct= 100% bioavailaiblity
Oral- via GI- we’ll tolerated but lower bioavailiablity
IM- slower, via capillary
Respiratory- across plasma men- rapid
drugs have to be
lipid soluble to pass membrane - therefor NOT IONISED
weak acids have
a low Ka, but a high pKA- pH at which 50% of the drug is ionised and 50% is nonionised
Distribution is referred to as
the volume of distribution
the volume of distribution
Vd
what is Vd
process by which drug is transferred from the blood to the tissue
- after absorption the drug equilibrates between the plasma and tissue
more detailed definition of Vd
‘vd represents the volume in which total amount of drug would need to be dissolved to match plasma conc’
what affects Vd
- drug size
- lipophilicity
- body composition
Vd=
Dosage/ conc of drug in plasma
Vd unit
mL
High plasma conc=
low Vd- drug not widely distributed
Low plasma conc=
high Vd - drug widely distributed
metabolism occurs in
the cell e.g. prodrug and in the liver = first pass metabolism
first pass metabolism
reduces bioavailability
- most drugs are metabolised slightly but the gut or the liver
- occurs in the LIVER and deactivates drugs
if first pass metabolism occurs
higher dose may occur
bioavailability is 100% if given via
IV
hepatic clearance
metabolism by the liver
renal clearance
exertion by the kidney
zero order drugs
constant AMOUNT of drug cleared per unit of time
first order drugs
constant PROPORTION of drug cleared per unit time
