Pharmacokinetics and Pharmacodynamics Flashcards
what is the therapeutic window
range of concentrations of the drug in the plasma to allow it to have its desired effect
what is the bioavaliabilty of a drug
the fraction of the drug administered which reaches circulation
what factors affect the bioavaliabilty of a drug
first pass metabolism, age, food, vomiting, malabsorption
what is first pass metabolism
where a drug can be metabolised before it reaches systemic circulation
where does first pass metabolism occur
gut lumen, gut wall and liver
what is the bioavaliabilty for a drug given by IV
100% as it reaches the blood immediately
how does protein binding affect the distribution of a drug
if drugs bind to plasma proteins then they are not active so cant have therapeutic effects
what is the volume of distribution
how far through the body compartments a drug will dissolve
how does the Vd change with weight
in patients with larger weights the Vd increases as the drug can travel through the fat better - this means he drug has less of an effect as theres a lower drug plasma concentration
what is the equation for Vd
Vd = Dose/immediate plasma concentration
what is the equation for bioavalibilty
AUCoral/AUCiv
which group of enzymes carry out the first stage of metabolism
CYP4500 enzymes
what do CYP4500 enzymes do
cause oxidation, reduction, hydrolysis in order to change the ionic charge of the drug
what does Phase II enzymes do
conjugate the drug e.g. with sulphate or glutathione to increase its solubility
what are pro-drugs
drugs which must be metabolised in order to become activated
what factors affect metabolism
hepatic disease, age, alcohol, smoking
what are the routes for drug elimination
kidney elimination, salvia, breast milk, sweat, bile
what 3 processes in the kidney affect elimination
glomerular filtration, passive tubular reabsorption and active tubular secretion
what happens to clearance if the GFR is decreased
clearance decreases
what happens to the half life if the GFR Is decreased
half life increases because less of the drug is cleared
what are first order kinetics
where the rate of clearance is proportional to the drug level
what are zero order kinetics
where the rate of elimination is constant
what is the hat life of a drug
amount of the it take for the concentration of a drug to half
what is the equation for half life
t1/2 = 0.7 x Vd/Cl
how does hepatic disease affect clearance
less metabolism can occur
how does cardiac disease affect clearance
less perfusion to kidneys and liver
what is a loading dose
where a higher concentration of a drug is given first in a repeated prescription in order to reach a steady state quicker
true or false - a loading dose is used in drugs with a low half life
false - its for drugs with a high half life
what is the equation for loading dose
loading dose = Vd x target drug concentration
what is tornado de pointes
where interactions between drugs leads to a slower conduction of the heart giving a prolonged QT internal
what is digoxin used to treat
AF with heart failure
why is a loading dose needed with digoxin
the drug has a long half life, however patient with AF need immediate treatment so you cant wait days to reach the steady state of the drug
what are the different types of antagonist
competitive (reversible and irreversible) and non-competitive
what is the therapeutic index
the relationship between the concentration of the drug causing adverse and desirable effects
what is the equation for the therapeutic index
toxic dose/effective dose
what is the affinity of a drug
how well a drug binds to a receptor
what does a low Kd say about the affinity of a drug
high affinity
what is the efficacy of a drug
the ability of a drug to produce a response
what is the potency of a drug
the dose required to give 50% response. same as EC50. the more potent a drug the better a response it can give at lower concentrations
what is intrinsic efficacy
the ability to bind to a receptor and cause a response.
what does the potency of a drug depend on
affinity and efficacy
what is Bmax
drug concentration when all receptors are bound
what is Emax
drug concentration giving 100% response
