Introduction to Pharmacokinetics Flashcards
What is pharmacokinetics?
Getting drugs to and from their site of action
What are the four steps of pharmacokinetics?
drug administration, drug absorption, drug distribution, drug elimination (metabolism and excretion)
What factors influence route of administration?
convenience, cost, bioavailability, whether you need a local or systemic effect
What factors influence distribution?
molecular size, ability to bind plasma proteins, lipid solubility
What are drug reservoirs?
Sites in the body where a drug can accumulate
What is volume of distribution?
Vd = X/C where X is amount of drug in body and C is concentration in plasma
What are the two forms of drug elimination?
excretion - in the kidney and metabolism in the liver
What are the steps in renal excretion?
glomerular filtration, tubular secretion (active), tubular reabsorption
What is the relationship between pH and lipid solubility?
acidic drugs are lipid soluble in low pH, basic drugs are lipid soluble in high pH
What is renal clearance?
glomerular filtration + tubular secretion - tubular reabsorption
When is an acidic drug more lipid soluble?
in low pH solutions
What is a basic drug more lipid soluble?
in high pH solutions
How do you treat aspirin overdose?
With sodium bicarbonate - because aspirin is an acidic drug a basic solution will make it less lipid soluble so it will not be reabsorbed and therefore will be excreted
What is renal clearance?
the amount of blood from which the drug is removed by the kidneys per time
What is the maximum renal clearance?
800mL/min (i.e. renal blood flow)
What is drug metabolism?
a chemical change to a drug
What is the main site of drug metabolism?
the liver
What is the main outcome of drug metabolism?
increase the water solubility and decrease the lipid solubility of a drug so that it can be excreted
What are the different types of metabolites that can be formed?
inactive, active in the same way as the parent compound, active in a different way to the parent compound, or toxic
What is phase I metabolism?
a reaction which creates a chemical functional group on a drug that it didn’t have before
What is phase II metabolism?
conjugation of a water soluble molecule to a functional group on a drug
What is the usual outcome of a metabolite from phase II metabolism?
it is inactive
Do phase I and phase II metabolism both have to happen?
No - can have just one of either or both
