Pharmacology Flashcards
bioavailability
proportion of administered drug that reaches the systemic circulation
pharmacokinetics
what the body does to the drug
pharmcodynamics
what the drug does to the boyd
to measure bioavailability
% of proportion measured relative to IV dose
IV administration mean
drug is 100% bioavailable
on a graph of bioavailability the area under it
is an indicator of total body exposure to the drug
factors which influence bioavailability
- nature of the drug (chemical, peptide)
- GI transit and digestion
- first pass metabolism
- route of admin
- lipophilicity
Bioavailability and GI transit and digestion
Patients with vomiting and diarrhoea have faster transit through GI tract- therefore tablets many not be totally absented.
patients who are sick
may not absorb any of the drug
drugs can be broken don by
enzymes in the GI tract
what is first pass metabolism
breakdown of drug by liver before it reaches systemic circulation
-blood flow from GI tract passes through liver via hepatic portal vein
route of admin e.g
- IV
- orally
IV
straight into the bloodstream
Oral
easy and well tolerated
IM
via capillaries/lympathic system- slower absorption
respiratory
across plasma membrane- rapid absorptions
administrations which involve
the drug accessing a blood supply quickly are the quickest
why is oral administration not perfect
due to first pass metabolism decreasing bioavailability
lipohilicity
the more lipophilic/hydrophobic molecules are the more that can pass through the phospholipid bilayer of cells, increasing conc of drug in tissues
many drugs are
weak acids
many drugs are weak acts so
are in equilibrium between ionised and unionised form
e.g.Uncharged + lipophilic or charged and lipophobic