Pharmacology Flashcards
Pharmacodynamics is…
What a drug does to the body
Pharmacokinetics is….
What the body does to a drug
Affinity is…
Strength of association between ligand and receptor
Efficacy is….
Ability of an agonist to evoke a cellular response
Antagonist is…
Drug that blocks the actions of an agonist
Agonist is…
Drug that binds to a receptor to produce a cellular response
Agonist possess ___________ while antagonist possess ________________ but lack _________
Affinity and efficacy
Affinity but lack efficacy
Competitive antagonism
Binding of agonist and antagonist occur at same (orthosteric) site
Competitive antagonism curve changes
Parallel rightward shift of agonist concentration response curve with no depression in maximal response
Non-competitive antagonism
Agonist binds to normal site and antagonist binds to separate (allosteric) site
Both may occupy sites simultaneously, but activation cannot occur when antagonist is bound
Non-competitive antagonism curve changes
Depress the slop and maximum response curve, but do not cause a rightward shift
Absorption is
Process by which a drug enters the body from its site of administration
Distribution is……
Process by which drug leaves circulation and enters the tissues perfused by blood
Metabolism is…..
Process by which tissue enzymes catalyse chemical conversion of a drug to a more polar form that is more readily excreted from the body
Excretion is…
Processes that remove the drug from the body
Factors Controlling Drug Absorption
Solubility
Chemical stability
Lipid to water partition coefficient
Degree of ionisation
T or F: Only ionised forms readily diffuse across the lipid bilayer
False → only unionised forms readily diffuse across the lipid bilayer
Volume of distribution (Vd) is….
Volume into which a drug appears to be distributed with a concentration equal to that of plasma
How is Vd calculated for IV preparation of drug
Vd = dose/plasma concentration
T or F: The higher the therapeutic ratio the safer the drug
True
How is Therapeutic Ratio calculated
Therapeutic Ratio = MTC/MEC
Therapeutic Ratio is…..
Any concentration of drug between the minimum effective concentration (MEC) and maximum tolerated concentration (MTC)
First order kinetics
Rate of elimination directly proportional to drug concentration → most drugs have this
Clearance is….
The volume of plasma cleared of drug in unit time
In first order kinetics, half-life is inversely proportional to _______________
Elimination rate constant
How is Rate of elimination calculated
Rate of elimination = Clearance x Plasma concentration
Half-life is
Time for the concentration of drug in plasma to halve
Loading dose is…
Initial higher dose of drug before stepping down to lower maintenance dose
It accelerates the time at which a steady state can be reached and when plasma concentration becomes adequate
Depolarisation
The membrane potential becomes less negative (or even positive)
Hyperpolarisation
The membrane potential becomes more negative
Sympathetic preganglionic neurones always _____ while post ganglionic neurone usually _______
ACh
Noradrenaline
Sympathetic system has ____________ outflow
Thoraco-Lumbar (T1-L2)
Effects of sympathetic system on the body
Increases HR and force of contraction
Relaxes bronchi, decreases mucus production
Reduces GI motility and constricts sphincters
Vasoconstriction but relaxation in skeletal muscle
Release of adrenaline from adrenal gland
Ejaculation
Parasympathetic preganglionic neurones always _____ while post ganglionic neurone usually _____
ACh
Parasympathetic system outflow from…
Cranial nerves III, VII, IX and X
Cranio-sacral outflow
Thoraco-lumbar outflow
Sacral spinal nerves
Effects of parasympathetic system on the body
Decreases HR
Bronchoconstriction, stimulates mucus production
Increases GI motility and relaxes sphincters
No effect on blood vessels or adrenal glands
Erection
Selective, competitive antagonist of a1
Vasodilator used as anti-hypertensive
Which drug?
Prazosin
Selective, competitive antagonist of B1
Used as an anti-anginal and anti-hypertensive agent
Which drug?
Atenolol
Selective agonist at B2
Used as bronchodilator in asthma
Which drug?
Salbutamol
Competitive antagonist of Muscarinic ACh receptors, does not block nicotinic ACh receptors
Blocks parasympathetic division of ANS
Used to reverse bradycardia post MI and in AChE poisoning
Which drug?
Atropine
What are the different G-protein coupled adrenoceptor subtypes and their functions at sympathetic neuroeffector junctions?
B1 – stimulates through Gs stimulating adenylyl cyclase increasing heart rate and force
B2 – stimulates through Gs stimulating adenylyl cyclase causing relaxation bronchial and vascular
a1 – stimulates through Gq stimulating phospholipase C causing contraction of vascular smooth muscle
a2 – stimulates through Gi stimulating inhibition of adenylyl cyclase causing inhibition of NA
What are the individual roles of muscarinic receptors M1, M2 and M3?
M1 – signals to specific G-protein (Gq) which stimulates phospholipase C which causes increased acid secretion in the stomach.
M2 – signal to specific G-protein (Gi) which stimulates inhibition of adenylyl cyclase which opens K+ channel causing decreased heart rate.
M3 – signals to specific G-protein (Gq) which stimulates phospholipase C production which causes increased secretion of saliva or contraction of visceral smooth muscle.
Which two receptors can ACh activate?
Nicotinic (ligand gated receptors)
Muscarinic (G-protein coupled receptors)
Describe how G-proteins function
Signal Agonist binds to and activates receptor
G protein couples with receptor
Guanine nucleotide exchange (GDP dissociates and GTP binds to alpha subunit)
Subunit dissociation (G protein dissociates into alpha subunit and beta-gamma subunit)
G protein alpha subunit combines with and modifies activity of effector to bring about the desired signal
Agonist may dissociate from receptor at any time, but signaling will still occur
Which is faster, ligand gated ion channels or G-protein coupled?
Ligand gated channels
Zero order kinetics
Drugs that are eliminated at a constant rate, regardless of their concentration
An increase in drug concentration will have no effect on the rate of elimination
How many half lives does it take to reach a steady state?
5
How is steady state calculated
Maintenance dose rate/clearance
Phase 1 metabolism of drugs causes change in drug via…..
Oxidation, reduction or hydrolysis
Phase 2 metabolism of drugs causes change in drug via…..
Conjugation of drug with a polar molecule to form a water-soluble metabolite
Conjugated product is readily excreted via the __________ in phase 2 metabolism
Kidneys
