Pharmacology Flashcards
What is a ligand?
Any substance that binds to a receptor i.e. drugs, hormones, neurotransmitters
Define affinity of a ligand to a receptor
The strength of attraction of a ligand to a receptor. It does not affect the effect the ligand has when bound to the recpetor
Define selectivity (of a ligand)
The capacity of a ligand to produce a specific effect (rather than a broad spectrum of effects)
Define specificity (of a ligand)
A ligands capacity to bind to a specific type of receptor only
What is lag time?
The time between administration of a drug and the appearance of pharmacological effects
Define full agonist
Full activation of a receptor - the same effect as the endogenous neurotransmitter
Define a partial agonist
A ligand that is an agonist at a receptor but doesn’t produce the full effect that an endogenous neurotransmitter would. E.g. buprenorphine at mu receptors. However it has a high affinity for mu receptors
Define an antagonist
A ligand that binds to a receptor but does not activate it. They can be competitive or non competitive. Flumazenil is a competitive antagonist
What is the difference between competitive and non competitive antagonists?
Competitive antagonists bind to the same receptor site as the agonist and can be displaced with higher concentrations of the agonist.
Non-competitive antagonists bind to the same spot or a different site on the receptor and are not displaced by increasing the concentration of the agonist - they are harder to shift!
Define a reverse agonist
A ligand that binds to a receptor and produces the opposite effect normally produced by the agonist ligands for that receptor. Eg if the agonist effect provides analgesia then the reverse agonist produces pain
What is an agonist-antagonist?
A ligand that has an agonist effect on some receptors and antagonist on others. E.g. butorphanol is an agonist at kappa receptors but an antagonist at mu receptors.
What is the significance of a drug being lipophilic or hydrophilic?
Lipophilic drugs have a faster onset and shorter duration of action because they pass through cell membranes more easily. E.g. fentanyl is more lipophilic (with shorter duration) than morphine which is more hydrophilic. This allows morphine to stay in the epidural space for longer.
Local anaesthetics are sodium channel blockers, how does this work?
Local anaesthetics such as lidocaine prevent generation of action potentials, via influx of Na ions through Na channels into the neve cell
How do GABA receptors work in regard to pain?
GABA is a neuro inhibitory receptor. It reduces CNS activity by causing hyperpolarization of the neuron.
How do NMDA receptors work?
Glutamate is the NT. Enough nociceptive stimulation and the Mg2+ plug is removed and the receptor is activated - leading to central sensitisation
Where are alpha adrenoceptors found and what is their function?
Alpha receptors are stimulatory except for those found on intestinal smooth muscle.
They cause vasoconstriction in vascular smooth muscle.
On the heart (stimulatory) A1 cause vasoconstriction and positive inotropy. A2 cause vasoconstriction, negative inotropy and reduced HR.
Where are beta adrenoceptors found and what is their function?
Beta receptors are inhibitory except for those on the cardiac muscle which produce positive chronotropic and inotropic effects. They have inhibitory (relaxing) effects on the bronchial & vascular smooth muscle (vasodilation) & GI & genito-urinary tissues
How does adrenaline and noradrenaline interact with alpha and beta receptors?
Noradrenaline has a more potent effect on alpha receptors than adrenaline (mix of a1 & a2), whilst adrenaline has a more potent effect on beta receptors than noradrenaline (HR & contractility).
Define potency
The concentration of a drug required to obtain a pharmacological effect - the less drug needed to produce an effect, the more potent it is
Define effective dose
The dose of a drug necessary to produce the desired effect in 50% of animals it is administered to
Define lethal/toxic dose
The dose of a drug necessary to induce death/toxic effects in 50% of animals it is administered to
Define therapeutic index
A measure of how safe a drug is - the higher the index, the more safe a drug is
Define therapeutic index
A measure of how safe a drug is - the higher the index, the more safe a drug is
Define total body clearence
A measure of how efficiently the body can eliminate a drug completely
What is the first pass effect?
Drugs taken orally pass through the liver first with varying levels of metabolism before entering systemic circulation and reaching the target organ
What is the second gas effect?
The ability of a low blood-gas solubility gas such as nitrous oxide (fast onset and recovery) to increase uptake of a more soluble inhalant such as isoflurane
What is blood gas coefficient?
A ratio to describe how soluble an inhalant gas is in blood. The higher the BGC, the more soluble and the slower onset and recovery. The lower the BGC, the faster onset and recovery. Lower BGC gasses like N2O can give second gas effect to inhalants with higher BGC.
What is bioavailability?
To what extent a drug enters the bloodstream and reaches the site of action to carry out the desired effect
What is context sensitive half life?
Context sensitive refers to how long an infusion has been given for and half life is the time it takes for plasma concentrations to drop by 50%. I.e the time it takes a drug to wear off depending on how long you give it for.
Define drug synergism
When the combined effect or two or more drugs is greater than the sum of the drugs individually.
E.g. alpha 2 agonists and opioids combined effects are better than the effects of them individually
