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pharmacodynamics
study of the mechanisms by which drugs produce changes in the physiological functions in the body
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4 ways drugs work
- interact with specific receptors
- alter activity of enzymes
- binding to ion channels or transport proteins
- act by nonspecific physical or chemical interactions
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where most receptors are located
outside surface of the cell membrane
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How most drugs exert their effects
interaction with specific drug receptors, leading to a change in the physiological function
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drug receptor
- usually a protein macromolecule produced by the body
- interacts with endogenous substance, will also interact with drug molecule with similar size, charge, shape and atomic composition
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endogenous substance
a substance produced by the body
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exogenous substance
a substance that is not produced by the body
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ligand
molecule that binds to the receptor
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ligand neurotransmitter at neuromuscular junction
Acetylcholine
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agonist
- drug that occupies and activates a receptor, thereby producing a cellular response
- affinity for receptor, efficacy at receptor, briefly occupies receptor
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intrinsic activity
efficacy
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antagonist
- a drug that occupies a receptor but does not activate the receptor
- affinity without efficacy. Occupies the space normally occupied by agonist/endogenous ligand.
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two types of antagonists
- Competitive/reversible (briefly occupy receptors, can be overcome)
- irreversible antagonists (permanently occupy, often covalent, to their receptors)
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competitive/reversible antagonist
briefly occupy receptors can be overcome with enough ligand.
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irreversible antagonists
permanently, often covalently, bind to their receptors
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Graded dose response curve
dose vs. response
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Threshold dose
dose that produces an observable effect.
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Ceiling effect
plateau of curve indicating that further increase in dose will not increase response (maximal efficacy of drug)
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Drug efficacy
the magnitude of the maximal response that can be elicited by a drug
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Drug potency
a measure of the quantity of drug required to obtain a particular response
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quantal dose response curve
population v. drug
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ED50 Median effective dose
in quantal dose response curve, the dose of a drug that produces a specified, desired effect in 50% of the animal population tested
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TD50 Median toxic dose
- The dose of drug which produces a specified toxic effect in 50% of the population tested
- Not death, can be treatable
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Therapeutic Index (TI)50
- TI = TD50/ED50
- The ratio. A really high TI is safe, lower is worse (bad effect/good effect)
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LD50 Medial Lethal Dose
the dose of drug that causes death in 50% of the animal population tested
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partial agonist
same effect at effective dose, much lower max efficacy. Cannot elicit a maximal response compared to a full agonist
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Adverse drug reaction
harmful or undesirable effect of a drug
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mechanism-based adverse drug reaction
a harmful or undesirable effect of a drug that is a PREDICTABLE extension of the principal pharmacological actions of the drug
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Idiosyncratic adverse drug reaction
a reaction to a drug that is particular to a specific patient, due to interactions of the drug with unique hose factors that are unrelated to the principal actions of the drug.
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side effect
any effect of a drug other than the one for which it is being used
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drug interactions
- a change in the pharmacological response of a drug due to the presence of a second drug
- Object drug is the drug acted upon
- precipitant drug influences other.
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Pharmacokinetic drug interactions
plasma or tissue levels are altered by the presence of another drug, causes changes in absorption, distribution, metabolism and/or elimination.
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pharmacodynamic drug interaction
- action or effect of drug is altered by another drug. Occurs at site of drug action.
- Include antagonistic (reversals), additive (2 drugs with same effect, seratonin syndrome) and synergistic (precip enhances effect of objecive, P450 blocker with cyclosporine b/c cyclo is so expensive, can use less)
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pharmaceutic drug interactions
The resulting physical or chemical reactions that take place as a result of mixing drugs in a container or syringe.
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