pharmacodynamics Flashcards
definition of pharmacodynamics
is the study of the mechanism of action of a specific drug
it is the relationship between drug concentration and responses that occur in the body due to the drug
why be concerned about how drug work?
knowledge of how a drug works increases the nurse’s confidence and it ensures that the drug is being used appropriately to prevent medication error.
improves the ability to educate, assess and evaluate patients
definition of mechanism of action
means the way a drug produces a therapeutic effect. once the drug hits its site of action it can modify the way a cell of tissue functions . mechanism of action of most drugs involve the interaction of the drugs with receptors or enzymes.
what is a drug-receptor
it is a specialised macromolecule to which a specific group of drugs or naturally occuring substances can bind
once the substance binds to and interacts with the receptor, a __________ is produced
pharmacologic response / therapeutic effect
what is the receptor theory?
it is when a drug molecule binds to a reactive site on the cell which is the receptor. once the substance binds to and interacts with the receptor a pharmacologic response/therapeutic effect is produced
_____+__________= drug affect
drug and receptor
what are the structures of receptors
most receptors are proteins found on the plasma membrane of a cell or tissue
some receptors are intracellular molecules such as DNA or enzymes in the cytoplasm
what is the function of receptors?
is to bind endogenous molecules
what are some examples of endogenous molecules?
hormones and neurotransmitters
when a drug binds to a receptor is can be classified as either :
agonist or antagonist
what is agonist?
agonist mimics the effect of the endogenous substance that normally binds to the receptor and produces the response
examples of agonist
epinephrine (adrenaline) neurotransmitter
the epinephrine neurotransmitter, at the adrenergic synapses, is an agonist. it is produced by the adrenals, it binds to the receptor and there is a response for our fight and flight
what is the antagonist?
drug occupies the receptor and prevents the endogenous substance from binding.
The drug binds to receptor prevents binding of agonist.
example of antagonist
alpha and beta adrenergic blockers
blockage of myocardial beta 1 receptors may
decrease force and rate of. contraction
what is affinity
affinity is the degree to which a drug binds with a receptor
the drug with the best ________ or _______ will elicit the best response
best fit or affinity
what are enzymes
enzymes are substances that catalyze nearly every biochemical reaction in a cell
drugs can interact with enzyme systems to
alter a response
Enzyme inhibitors _______ action of enzymes
inhibits
what is the function of enzyme inhibitors
it inhibits action of enzymes. the enzyme is fooled into binding to a drug instead of a target cell. it protects target cell from enzyme’s action.
what do ACE ( angiotensin-converting enzyme inhibitors) inhibitors do?
it reduced blood pressure
how does an enzyme system work?
1) substrate enters the active site of the enzyme
2) enzyme-substrate complex forms
3) substrate is converted to products
4) products leave the active site of the enzyme
what are non-specific interactions?
some drugs bypass the enzyme system. MOA of some drugs is that they do not go to a receptor site or alter an enzyme function.
main site of action is cell membrane or cellular process. these drugs will physically interfere or chemically alter cell process. final product is altered causing defect or cell death.
where is the main site of action of non-specific interaction drugs?
cell membrane
examples of non-specific interaction drugs
cancer drugs, antibiotics
what is a therapeutic index
it is the measure of the safety of a drug
it is the ratio between a drug’s therapeutic benefits and its toxic effects.
therapeutic index formula
median lethal dose LD50/ median effective dose ED50
what is a median lethal dose (LD50)
the amount of drug that will be lethal in 50% of a group of animals
what is a median effective dose (ED50)?
the amount of a drug required to produce a response in 50% of the subjects to whom the drug is given
low therapeutic index =
not good because it means the safety margin is small
what is the relationship between the therapeutic index and safety of a drug
the higher the TI, the safer the medication
larger the TI, the _____ the drug
safer
must be > ___ for the drug to be usable
1
when a drug is given to a single patient, the intensity of the response can be seen in a ____________
drug-response curve
how many phases in drug-response curve?
3
what happens during phase 1
occurs at lowest dose . few target cells affected by drug
what happens during phase 2
linear relationship. linear relationship between amount of drug administered and degree of client response. i.e doubling the dose doubles the drug response
which phase is the most desirable
phase 2
what happens during phase 3
increasing dose has no therapeutic effect
the increased dose may produce adverse effects
what is potency
refers to the measure of how much a drug is required in order to produce a particular effect.
what is efficacy
refers to the magnitude of the maximal response that can be produced by the drugs
drug interaction may occur with either
with either drugs or food
what are drug-drug interactions
changes in a drug’s effect caused by the presence of another drug taken during the same period
type of drugs which are at risk of drug interaction
- narrow TI (low safety drug)
- steep dose-response curves
- drugs where a loss of effect may lead to disease breakthrough
why do drugs with steep dose-response curves at risk of drug interaction
a minor change in plasma concentration may take a major change in effect example warfarin
patients who are at risk of drug interaction
- elderly, polypharmcy, poor homeostatic mechanism
- severely ill patients
- patients who depend on prophylactic therapy for disease suppression
those who are at risk of drug interaction
patient with renal of liver disease
patient with more than one physician
types of drug-drug interactions
duplication
opposition (antagonism)
alteration
describe and explain what happens during duplication
duplication may occur when a person inadvertently takes two drugs, that have the same active ingredient.
when two drugs with the same effect are taken, their therapeutic effects and their side effects may be intensified.
what is opposition
when two drugs with opposing actions interact, reducing the effectiveness of one or both
what is alterations
one drug may alter how the body absorb, distributes, metabolizes, or excretes another drug
what are drug-food interactions
changes in a drug’s effects caused by food consumed in the same period of time
presence of food in the digestive tract may _____________ of a drug
reduce absorption
what happens when warfarin interact with foods rich in vitamin k such as broccoli, spinach
reduce the effectiveness of anticoagulants (warfarin) increasing the risk of clotting. intake of such foods should be limited and the amount consumed daily should remain constant
what happens when tetracycline interact with calcium foods
these foods can reduce the absorption of tetracycline, which should be taken 1 hour before or 2 hours after eating
what happens when statins interact with grapefruit
grapefruit contains substance that affects the intestinal absorption of drugs such as statins
what is drug-medicinal herb interactions
drugs interact with certain medicinal herb or supplement taken by patients at the same time
what is an adverse drug reaction
is an adverse outcome of drug therapy in which a patient is harmed in some way
causes of ADR
pharmacologic reactions
hypersensitivity reactions
idiosyncratic reactions
Pharmacologic reactions are ________, ______ -related, , occurs due to _________
predictable, dose, action of drug
hypersensitivity reactions are _______-related , requires _____________, _______ develop when drug acts as antigen or allergen , ______________ produces hypersensitiy reaction
not dose, prior exposure, allergies, subsequent exposure
idiosyncratic reactions are ___________, ______-realted or allergic, occurs in __________ percentage of people
unexpected, not dose-related, small
ADRS is also known as
side effects
if a drug is teratogenic
it causes fetal malformation
if a drug is mutagenic
it causes mutations of DNA
if a drug is carcinogenic
it causes cancer
if a drug causes tolerance
there is a decreasing response when repeated doses are given
if a drug causes dependence
patients have a physiologic or psychological need to a drug
