What effect does a drug have upon a cell once it binds to a recepter?
Response is either to block or mimic normal receptor activity, ie, a drug cannot artificially make a cell do anything it cannot do naturally.
What is responsible for the number/types of side effects a drug can have?
The number of different types receptors, ie a master key for one door versus specific key for one lock
Increased receptor response increases potential for side effects, but selectivity does not guarantee safety of drug.
What is simple occupancy theory?
- Assumes ability to bind and influence receptor.
- Intensity of response proportional to the number of similar receptors occupied.
- Maximal response occurs when all available receptors have been occupied after which increasing the dose will have no further effect.
What is the Modified Occupancy Theory?
- Assumes affinity and intrinic activity are mutually exclusive.
- Affinity~Strength of attraction between drug and receptor, high affinity drugs are very potent.
- Intrinsic activity~Ability of drug to activate receptor after binding, high intrinsic-activity drugs have maximal efficacy.
What is the Dose Response Curve?
- Most important characteristic is that the response is graded.
- As the dosage is increased…the response becomes progressively larger, therefore...
- ...you can individually adjust the response for each patient
What are the phases of the Dose Response Curve?
- Phase I
- Occurs at low doses…the curve is flat during this phase as the amount of drug is too low to elicit a measurable response
- Phase II
- An increase in dose produces a corresponding increase in response. During this phase the response is “graded”
- Phase III
- Eventually a point is reached where an increase in dose is unable to elicit a further increase in response…the curve then flattens out
Explain the concepts of Maximum Effect and Relative Potency.
: The largest effect that a drug can produce. Reflected by the height of the dose-response curve. It is what the body is doing when cell receptors are maxed out.
- Relative Potency: Amount of drug that must be given to elicit an effect as compared to a similar drug, ie drug A is more potent than drug B because I can give less of A to elicit the same response as B.
- Note: Potency and Maximum Effect are completely independent of each other.
What sort of drug is an Agonist?
- Mimics action of endogenous regulatory molecules.
- Have affinity and high-intrinsic activity--> increased cellular response-->increased effect.
What sort of drug is an antagonist?
- Block actions of endogenous regulatory molecules meaning...
- ...if no agonist present then no affect by antagonists because although the antagonist is blocking the receptor sites there is nothing present to activate them anyway, however...
- ...if agonist present…then antagonist can shut down/prevent an action that would have otherwise occurred.
What are to classes of Antagonistic drugs?
Competitive: Bind reversibly. In presence of two or more competative antagonists, the one will highest affinity will bind but will become unbound with the introduction of a new drug/molecule with higher affinity which will then take its place.
Noncompetitive: Bind irreversibly. Once bound, the drug must run its course before it will become unbound from a receptor.
What is a partial Agonist?
A drug which binds to a receptor to elicit a repsonse, but with a lower intensity than what might otherwise occur. There it can act as both an agonist (produces an effect) and an antagonist (blocks drugs/molecules which might otherwise elicit a greater effect).
How are cell receptors classified?
- According to affinity for types of agonist/antagonists, ie:
- Adrenergic system (adrenergic = release of epinephrin, norepinephrin, or similar at synapses of nerves composing sympathetic nervous system. ) Can be Alpha angonist/antagonist or Beta agonist/antagonist.
Can also be classified according to location within the cell or cell membrane.
What are the 4 primary receptor families?
Cell membrane embedded enzymes, ie growth factors and insulin
Ligand-gated ion channels: “Transducers," Amplify signals received
G protein-coupled receptor systems: Can stimulate or inhibit a wide array of activities
Transcription factors: Requires hours to days for full effect because it is a complex system which starts with increasing transcription of DNA--> RNA, then RNA--> amino acids/proteins, then circulation, then finally proteins binding to their target receptors. ie Thyroid hormone
What is an idosyncratic drug reaxtion?
A reaction predicated upon genetic differences between patients.
What is the difference between an idosyncratic reaction and an allergic reaction?
An allergic reaction is specifically a histamine reaction and can be caused either by the drug itself or its metabolites.
What are some clinical implications of interpatient variability
Initial dose is an approximation…fine tune subsequent doses
With an average ED50, some patients will be undertreated, others overtreated
Doses not completely predictable; need to look at patient reactions/responses to the drug.
Actual response must be evaluated
What is the Therapeutic Index?
- Measure of drug’s safety indicated by a specific number.
- =LD50/ED50; Ratio indicates how safely a drug can effectively be used.
Low index=closely monitored blood serum levels.