Pharmokinetics Flashcards
what is pharmokinetics?
what the body does to the drug
changes over time of drug and metabolite concentrations within body fluids
what is a body compartment?
we can simplify a human and call it compartment, with volume V
we can then calculate the concentration C of an introduced drug of a known quantity C
what is the general process of drugs in the body?
absoprtion
distribution
metabolism
excretion
what is absorption and distribution?
how much drug reaches th target site per unit time
what is metabolism and excretion?
how much drug is removed from target site per unit time
what is plasma?
the liquid component of blood and this is how drugs move around the body
what are six methods of drug administration?
intravenous intramuscular/subcutaneous oral rectal inhalation transdermal
what must a drug achieve in order to be absorbed?
the drug must be able to cross membranes
what are four methods of membrane crossing of drugs?
diffusion through lipid membrane, diffusion through aqueous pore channels formed by aquaporins, via membrane transporters, or via pinocytosis
which factors determine how well a drug can diffuse through a membrane?
lipid soluble drugs cross easist
lipid solubility is determined by ionisation
most drugs can exist in ionised or un-ionised (protonated) forms
describe protonated drug forms…
HA
lipid soluble and can therefore easily cross cell membranes
describe ionised drug forms…
not lipid soluble and so need specific transport mechanism to cross membranes
how do pH and pKa influence ionised state?
when pKa is greater than pH, apirin in protonated HA state
what are the functions of the BBB?
regulate movement
exude toxic substances
protect neurons
how do drugs cross the BBB?
anything lipid soluble can diffuse through endothelial cells
ion channel exchanges
receptor mediated transport
what are three examples of phase 1 metabolic processes?
oxidation
reduction
hydrolysis
what are two examples of phase 2 metabolic processes?
synthetic (add something)
attach something to reactive group of derivative
what is ‘first pass’ (presystemic) metabolism?
occurs to drugs that are extracted by the liver or gut wall before they can reach systemic circulation
need much greater dose and individual variations
what are three excretion pathways in the body?
glomerular filtration
passive reabsorption
active tubular secretion
what is drug clearance?
the rate of removal of drug from the bloodstream
what are two kinetic models than can be applied to describe drug clearance?
first order kinetics (related to plasma concentration)
zero order kinetics (independent of plasma concnetration, dependent on something other than drug availability, i.e. enzyme availability)
what are five factors that affect drug clearance half-life?
type of enzyme enzyme induction enzyme inhibition enzyme competition metabolic variability between patients
