Pharmacology Flashcards
What is pharmacokinetics?
How the body affects the drug - absorption, distribution, metabolism and excretion of the drug
What is pharmacodynamics?
How the drug affects the body
What are the different kinds of receptors?
GPCRs e.g. beta-adrenoceptors
Ligand-gated ion channels e.g. nAchR
Kinase-linked receptors e.g. VEGFR
Cytosolic/nuclear receptors e.g. oestrogen receptor
What is an agonist?
A compound that binds to receptors and activates it; it can reverse the effect of an antagonist in competitive inhibition
What is an antagonist?
A compound that reduces the effect of an agonist; it does not activate the receptor and can reverse the effects of an agonist in competitive inhibition.
What is EC50?
The concentration of the drug that gives half the maximal response.
What is Emax?
The maximum possible effect of the agonist
What is intrinsic activity?
Intrinsic activity = Emax of partial agonist + Emax of full agonist
What is affinity?
How well a ligand binds to a receptor; it is a property shown by both agonists and antagonists
What is efficacy?
How well a ligand activates a receptor; only agonists have efficacy
What is tolerance?
A reduction in drug effect over time with continuous, repeated high concentrations of the drug. This is a clinical description.
What is desensitisation?
The mechanism through which tolerance occurs. It happens though:
Desensitisation of the receptors either by uncoupling them, internalising them or degrading them.
What is receptor-reserve?
An integrative measure of the response-inducing capacity of an agonist and of the signal amplification capacity of the corresponding receptor.
What are the three phases of plasma levels?
Uptake into plasma
Distribution from plasma
Elimination from plasma
What is the rate of diffusion for a dissolved drug?
Rate of diffusion is proportional to the concentration gradient (first order process with respect to concentration)
1/ distance to diffuse
Rate of diffusion is proportional to temperature
What are the compartments of the body and how much fluid is in there?
Plasma - 5L
Interstitial - 15L
Intracellular - 45L
What are the different mechanisms of movement?
Simple diffusion Facilitated diffusion Active transport Through extracellular spaces Non-ionic diffusion
What is bioavailability?
The amount of drug taken up as a proportion of the amount administered.
What are the two main routes of elimination for drugs?
Hepatic elimination and renal elimination.
What is clearance?
The volume of plasma that can be completely cleared of the drug per unit of time.
The rate at which the plasma drug is eliminated per unit of plasma concentration.
Both are measures of efficiency and are measured in ml/min
How are water soluble molecules eliminated in the kidneys?
They pass through the glomerular endothelial gaps and are eliminated by glomerular filtration.
How are larger water soluble eliminated in the kidneys?
Through active tubular secretion
How is clearance calculated?
The rate of appearance in urine / plasma concentration
What does clearance assume?
The rate of elimination is equal to the rate of appearance in the urine
What causes impaired renal clearance?
Acutely - reduced perfusion causing AKI
Chronically - HTN or DM causing CKD
What effect does hypoalbuminaemia have on drug clearance?
Lipid soluble drugs have higher freely diffusible fractions and greater effects. Elevated plasma creatine and urea compete for lipid binding sites on protein and displace more drug.
What adjustments need to be made for renal impairment?
Choose drugs not eliminated renally
Avoid nephrotoxic drugs
Measure plasma concentrations if there’s a toxicity risk
Haemodialysis and give normal doses as usual
How are drugs eliminated renally?
Through active transport systems; they vary in efficiency for different compounds.
What is the hepatic extraction ratio?
The proportion of the drug that is removed by one pass through the liver.