Pharmacology Flashcards
Define ‘pharmacology’
The study of substances that interact with living systems through chemical processes
Define ‘drug’
Any substance that interacts with a molecule which plays a regulatory role in living systems
What is a ‘competitive antagonist’?
Binds to and competes for receptor but elicits no reaction
What is a chemical antagonist?
Substance that binds directly to an agonist molecule to prevent it from binding to the active site
What is a physiological antagonist?
When two substances have exactly opposite actions and work via different pathways
What is ‘pharmacodynamics’
the action of a drug on the body
What is pharmacokinetics?
The action of the body on a drug
What do drugs tend to be? (related to pH)
weak acids or bases
When are drugs lipid-soluble?
In their undissociated (non-charged) form
When are drugs water-soluble
In their dissociated (charged) form
What can activated charcoal be used for?
Absorbing substances in the GI tract, especially those from overdose
How may you treat a TCA overdose and why?
TCA is a weak acid so can be treated by trying to alkalinise the blood to cause dissociation into water-soluble form in order to prevent diffusion back into the blood from the renal tubule
How may you treat an amphetamine overdone and why?
Amphetamines are weak base so acidify urine by administering ammonium chloride in order to increase excretion
Define ‘drug specificity’
The ability of a drug to act on a particular location alone
Define ‘drug selectivity’
The ability to produce a particular effect as a result of the structural specificity of drug binding to receptors
What are the 4 different types of bond? (order in terms of strength)
Covalent, electrostatic, hydrophobic and van der waals
What does ‘EC50’ represent?
The concentration of drug that gives a half-maximal response
How does EC50 change in the presence of competitive antagonists?
Need to add more drug in order to reach EC50
How does EC50 change in the presence of non-competitive antagonists?
The maximal effect of the drug is reduced, but the EC50 therefore remains the same
Define ‘efficacy’
The greater the effect of the drug, the greater the efficacy
Define ‘potency’
The concentration of a drug required for that effect to have the same efficacy
What is volume of distribution?
Amount of drug in body/plasma concentration - it is a measure of the distribution of the drug around the body
What protein may drugs bind to?
Albumin in the blood
What are the properties of ‘bound’ drugs (to proteins)?
They cannot be metabolised, excreted or diffuse through structures, they are inactive
What happens if you stop or start a drug that binds to a protein?
It changes the level of other protein-bound drugs and can lead to both drugs having sub-therapeutic levels
What are the 4 types of receptor drugs may act on? (order in terms of fast to slow)
Ligand-gated ion channel, G protein-coupled receptor, receptor tyrosine kinases and nuclear receptors
Define ‘tachyphylaxis’
Reduced drug effect in a short time scale
Define ‘tolerance’
Reduced drug effect when given over a long period of time
What may be the cause of tachyphylaxis and tolerance?
Receptor loss or desensitisation, physiological adaptation, exhaustion of mediators, increased metabolic degradation or receptor internalisation
How does salbutamol act?
It’s a B2 adrenergic receptor agonist
Why may tachyphylaxis occur with salbutamol?
There is polymorphism of the B2 adrenergic receptor on which salbutamol acts
Which routes of drug administration experience first pass metabolism?
Oral and rectal; go to liver prior to entry to systemic circulation
What is the ‘first pass effect’?
All drugs absorbed by GI tract enter the portal blood supply and travel to the liver where they are metabolised by enzymes before entering the systemic blood supply
What is involved in phase I reactions?
Biotransformations to make substances more water-soluble (polar) as well as reduction, hydrolysis and oxidation (CYP450 involved) reactions
What is involved in phase II reactions?
Entry to phase II if still not polar enough after phase I, conjugation (adding large molecule such as glucose to increase water-solubility) and synthesis
What is meant by ‘clearance’?
The rate of elimination/concentration remaining
Define ‘half-life’
time for the drug plasma concentration to halve
How do you calculate drug half life?
volume distribution/clearance x 0.7
Define ‘zero order metabolism’
Where elimination is constant per unit of time, so graph is linear, this only occurs when the elimination system is saturated (ethanol)
Define ‘first order metabolism’
Elimination of constant fraction of drug per unit of time (bell shaped graph), so the half-life is always constant
Define ‘loading dose’
Larger than normal dose used to get individual into therapeutic window more quickly
Define ‘maintenance dose’
Keeps the drug in therapeutic range
