drug absorption Flashcards
what is the pharmaceutical process?
getting the drug to the patient
what is the pharmacokinetic process?
getting the drug to the site of action
what is the pharmacodynamic process?
producing the correct pharmacological effect
what is the therapeutic process?
producing the correct therapeutic effect
what does ADME stand for and what does it determine?
Absorption Distribution Metabolism Elimination these factors determine drug pharmacokinetics
what routes of administration are there for drugs?
oral IV subcutaneous intramuscular other GI - sublingual, rectal inhalation nasal transdermal
why do drugs have to be absorbed to be effective?
they have to enter the bloodstream and make their way to the potential site of action
what is the Tmax?
time taken for the drug to reach peak concentration
what is the Cmax?
the peak concentration of the drug
what is the AUC?
area under the drug concentration/time curve on a graph
what does the AUC represent?
the amount of drug which reaches the systemic circulation
what does a high tmax indicate?
high rate of absorption
what is the therapeutic range?
the range of concentrations over which a drug is active
what is the therapeutic index?
a measure of the range at which the drug is safe and active
what is drug bioavailability?
the amount of drug which reaches the circulation AND which is available for action
how much of a drug given intravenously is bioavailable?
100%
what are some factors affecting bioavailability?
formulation ability of drug to pass physiological barriers (particle size, lipid solubility, pH and ionisation) GI effects (gut motility, food, illness) first pass metabolism
do drugs completely ionise in water?
not usually, some exceptions
what does the degree of ionisation depend on?
the pH of the environment, since most drugs are weak acids or bases
can the ionised form of a drug cross a membrane?
no
what would stop the un-ionised form of a drug from diffusing across a membrane?
when equilibrium is released
what is the ability of a drug to diffuse across a lipid barrier expressed as?
lipid-water partition coefficient
what is the lipid water partition coefficient?
ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact
what is first pass metabolism?
metabolism of drug prior to reaching systemic circulation
what things can affect first pass metabolism?
gut lumen (acid, enzymes) gut wall (metabolic enzymes) liver (hepatic extraction ratio)
what advantages are there to sub-cutaneous/intra muscular administration?
avoids first pass metabolism
what advantages are the of sublingual/buccal administration and give an example of a drug administered this way
avoids first pass metabolism
GTN spray
when would rectal administration of a drug be considered?
if a drug irritates the stomach (absorption is slow and avoids first pass metabolism)
what are the advantages of inhalation of a drug?
rapid action -delivered directly to site of action in case of asthma, for example
better for volatile agents
what are the advantages of transdermal application of a drug?
avoids first pass metabolism
can provide controlled release
what conditions need to be met for a drug to be given transdermally?
needs to be non irritant
what considerations would be mode prior to deciding which mode of administration to take?
purpose and site of drug action disease effects patient ability to take medicine speed of action reliability of absorption
