drug absorption Flashcards
four basic factors which determine drug pharmacokinetics
- absorption
- distribution
- metabolism
- elimination
ways of drug administration
- oral
- IV
- subcutaneous
- intramuscular
- sublingual (under the tongue)
- rectal
- inhalation
- nasal
- transdermal eg, with patches
drug absorption
the process of movement of unchanged drug from the site of administration to the systemic circulation.
Tmax
the time to peak concentration
Cmax
the peak concentration
AUC
area under the drug concentration curve
what does AUC tell us?
the amount of drug which reaches the systemic circulation (bioavailability)
therapeutic range
the range of concentrations over which a drug is effective
what happens if a drug conc. is below the therapeutic range?
there will be insufficient or no pharmacological action
what happens if a drug conc. is above the therapeutic range?
toxicity
therapeutic index
a measure of the range at which a drug is safe and active
bioavailability
the amount of drug that reaches the circulation and is available for action
what is the bioavailability of a drug given intravenously?
100%
factors affecting bioavailabilty (oral absorption)
- formulation- preparations that might cause a slow release
- ability of drug to pass physiological barrier
- gastrointestinal effects
- first pass metabolism
factors that affect a drug’s ability to pass physiological barriers
-particle size
lipid solubility
-pH and ionisation
gastrointestinal effects that effect bioavailability
- gut motility
- food
- illness
first pass metabolism
the metabolism of drugs rapidly by liver before it reaches the systemic circulation
physiological barriers
- passive transport
- filtration
- bulk flow
- active transport
- facilitated diffusion
- ion-pair transport
- endocytosis
Henderson-Hasselbalch equation
describes the relationship between the local pH and the degree of ionisation
where will highly lipid soluble drugs collect?
brain, ovaries, testes and liver. so levels of the drug above the therapeutic range will cause damage in these places.
lipid-water partition coefficient
The ability of a drug to diffuse across a lipid barrier. the ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact
what must a drug resemble to undergo active absorption?
naturally occurring compounds
bulk flow
the movement of water and solute due to a pressure gradient.
filtration
drugs move through channels in cell membrane
gastrointestinal factors that affect drug absorption
-motility
-food
illness (malabsorption, migraine reduces rate of stomach emptying so absorption decreases as drug doesn’t make it to small intestine as fast)
sites of first pass metabolism
Liver
gut wall
gut lumen
ways of administration that bypass first pass metabolism
- IV
- intra-muscular
- subcutaneous
- sub-lingual
- sub-buccal
- rectal
- transdermal
