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study of the mechanisms by which drugs produce changes in the physiological functions in the body
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
where most receptors are located
outside surface of the cell membrane
How most drugs exert their effects
interaction with specific drug receptors, leading to a change in the physiological function
- 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
a substance produced by the body
a substance that is not produced by the body
molecule that binds to the receptor
ligand neurotransmitter at neuromuscular junction
- drug that occupies and activates a receptor, thereby producing a cellular response
- affinity for receptor, efficacy at receptor, briefly occupies receptor
- a drug that occupies a receptor but does not activate the receptor
- affinity without efficacy. Occupies the space normally occupied by agonist/endogenous ligand.
two types of antagonists
- Competitive/reversible (briefly occupy receptors, can be overcome)
- irreversible antagonists (permanently occupy, often covalent, to their receptors)
briefly occupy receptors can be overcome with enough ligand.
permanently, often covalently, bind to their receptors
Graded dose response curve
dose vs. response
dose that produces an observable effect.
plateau of curve indicating that further increase in dose will not increase response (maximal efficacy of drug)
the magnitude of the maximal response that can be elicited by a drug
a measure of the quantity of drug required to obtain a particular response
quantal dose response curve
population v. drug
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
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
Therapeutic Index (TI)50
- TI = TD50/ED50
- The ratio. A really high TI is safe, lower is worse (bad effect/good effect)
LD50 Medial Lethal Dose
the dose of drug that causes death in 50% of the animal population tested
same effect at effective dose, much lower max efficacy. Cannot elicit a maximal response compared to a full agonist
Adverse drug reaction
harmful or undesirable effect of a drug
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
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.
any effect of a drug other than the one for which it is being used
- 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.
Pharmacokinetic drug interactions
plasma or tissue levels are altered by the presence of another drug, causes changes in absorption, distribution, metabolism and/or elimination.
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)
pharmaceutic drug interactions
The resulting physical or chemical reactions that take place as a result of mixing drugs in a container or syringe.