Introduction to Pharmacology Flashcards
Pharmacodynamics vs Pharmacokinetics
Pharmacodynamics is how a drug affects the body
Pharmacokinetics is how the body affects the drug
General ligand-receptor
Receptors lie on the cell boundary, ligands bind extracellularly which then triggers an intracellular signal, this cascades into a biological action
Channel linked receptors
Ligand binds to a recepter on an ion channel which can either signal the channel to open or close
G-protein coupled receptors
Interacts with a g-protein which in turn interacts with an ezyme activator or ion channel. So it indirectly interacts with these vis the g-protein
Enzyme (or Kinase) linked receptors
These directly initiate enzymatic interactions
Nuclear receptors
This stimulates messenger RNA synthesis in the cell nucleus leading to protein synthesis
They are intracellular
3 drug targets other than receptors
- Channel blockers, these target ion channels but block them instead of binding to a receptor on the channel
- Ezymes, these drugs directly target an enzyme
- Protein transporters, this target proteine transporters in order to enter a cell
Max drug response
This occurs when all the drug targets are already targeted and hence saturated. At this point increasing the dose won’t increase the response.
What is ED50
This is the dose at which 50% of the maximum response is reached
What is therapeutic index
This is the ratio of the ED50 of the desired effect and the ED50 of the adverse effect
What is a competative antagonist
These are molecules which bind to the same receptors as an agonist but don’t cause any intracellular signal transduction
Efficacy vs Potency
What do both of them mean and which of these drugs is more efficatious/potent
Efficacy is how large a response the drug has and potency is how much you need to produce an effect.
Drug C is the most potent and drug A is the most efficatious
What is a non-competative antagonist
These are molecules which don’t bind to the receptors but block further signal transduction
What does selectivity mean?
This is how specifically a receptor is targeted, if a drug bind to two different receptors equally then it is not very selective, but if it binds to one a lot better than another then it is highly selective.
Tachyphylaxis vs Tolerance
Tachyphylaxis is where desensitisation occurs rapidly whereas tolerance occurs gradually
4 reasons why drug desensitisation occurs
- The number of receptors reduce
- The structure of receptors or their function changes
- Mediators become exhausted
- Physiological adaption, the body produces physiological responses to counter the effects of the drug
What does it mean for a drug to survive “first pass metabolism”
First pass metabolism occurs through oral ingestion and is when a drug is metabolised by enzymes either in the intestine or the liver before it can reach the blood.
What is bioavailability?
This is how much of the drug makes it into the circulatory system and stays in the circulatory system.
In the graph below the ratio of the two areas under each line is the bioavailability, in this case it is 30% if taken orally
3 types of drug diffusion accross a membrane
- Passive
- Pore mediated
- Pinocytosis (large drug drags a whole part of the membrane with it to enter)
Protein binding of drugs and what this can mean
This is how efficiently a drug binds to proteins. A drug bound to proteins in blood plasma can’t diffuse into the interstitial fluid however it also can’t be eliminated from the blood.
The ratio of free drug to bound drug remains the same as the more free drug there is the more becomes bound.
Drugs that are highly protein bound are long acting and have long half lives.
They are also affected by things that affect blood plasma such as pregnacy, disease and age
Apparent volume of distribution
This is the total amount of the dosage administered divided by concentration in blood plasma.
Theoretically this tells you the apparent amount of plasma required to carry your dose at the measure concentration. But clinically it is essentially a measure of how much the drug has spread out into the body.
A higher apparent volume of distribution means the drug has spread into the body well, a lower means most has remained in the blood plasma.
Organs responsible for drug metabolism
Primarily metabolised by the liver however they can also be metabolised by the kidneys, lungs and skin
What are the two phases of drug metabolism?
- Phase 1: reacted into an in active compound
- Phase 2: reacted into a soluable compound for excretion
Why is it important for drugs to be water soluable during excretion?
If a drug is lipid soluable it will be able to pass through lipid membranes and re-absorb into the body from urine
Renal vs Biliary excretion
Renal excretion occurs with small drugs < 300Da and Biliary excretion occurs with large drugs > 300Da
Family of liver enzymes responsible for phase 1 metabolism
Cytochrome P450 emzymes
First order kinetics
Also known as exponential kinetics, concentration follows a typical half life pattern.
This is most typical as concentrations of the drug will affect the ammount that is metabolised
Zero order kinetics
This is where the ability to metabolise is maxed out very quickly hence a continous ammount is matabolised no matter what the concentration. An example include ethanol and aspirin.
What is steady state? If you dose once every halflife when is it reached?
This is where the rate at which a drug is being metabolised equals the rate of adminstration.
If you dose once every halflife then this is considered reached after 5 halflives.
Long vs Short half life advantages and disadvantages
Long:
* Patients don’t have to take it as regularly and the steady state is rather stable however it take longer to reach steady state
Short
* Has to be taken really regularly however as steady state is reached quickly you can play around with it lots more easily
What are beta 2 receptors responsible for?
Beta 2 receptors are predominantly present in airway smooth muscles.
When bound the airways relax
What are beta 1 receptors responsible for?
Found throughout the sypathetic nervous system including the heart and are activated by adrenaline and noradrenaline
