Pharmacology Concept 2
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Transcript of Pharmacology Concept 2
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8/4/2019 Pharmacology Concept 2
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Compiled by Venina Navuta
22/8/11
Pharmacology Concepts 2
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Terminology
Drug: substance or chemical thatalters physiological or biochemicalpattern. Used in diagnosis, prevention
or treatment.Drug action: interaction of drug withspecific sites cells, receptors or at sub
cellular level. (Usually Invisible)Drug effect: consequences of drug
actions leads to notable change like
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Agonist: has affinity to specificreceptors where it exhibits its action
(intrinsic activity)
Antagonist: binds to the receptors of
agonist and lacks activityPartial agonist: has some less affinity
and less intrinsic activity. Has same
actions as agonist but of less degreeat the same time blocks the receptor
for agonist to bind.
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Efficacy the ability to producearesponse
Potency the dose range over which a
response is produced
Tachyplaxis a decrease in the responseto a drug due to previous exposure tothat drug
Therapeutic index the ratio between thetoxic dose and the therapeutic dose of adrug used as a measure of the relative
safety of the drug for a particular
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Dose-Response Relationship
Relationship between the size of anadministered dose and the intensity ofthe response produced
The dose-response relationships formost drugs are graded i.e. responsegets more intense with increasingdosage
Because they are graded, therapeuticeffects can be adjusted to fit theneeds of each patient
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Types of drug responses
For drug to act should reach a criticalconcentration at its site of action
Above critical concentration. Drug
exhibits response related to dose up tocertain range till its maximumtherapeutic response is reached
Once maximum drug response isreached rise in dose has noenhancement in response but leads to
increase in toxic effects.
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3 Phases of Dose-response
relationship
Phase 1 occurs at low doses, too low toelicit a measurable response
Phase 2- an increase in dose elicits a
corresponding increase in the response.This phase is where dose-responserelationship is graded
Phase 3a point where an increase indose is unable to elicit a further increasein response, the curve flattens
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Maximal Efficacy & Relative Potency
Maximal efficacy
the largest effect that a drug canproduce
Indicated by the height of the dose-response curve
drug with high maximal efficacy isnot always more desirable than adrug with lower efficacy
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Relative Potency
Amount of drug that we must give inorder to elicit an effect
Potent drug is one that produces its
effects at low dosesPotency and efficacy are 2
independent qualities.
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Receptors through which drugs actare normal points of control ofphysiologic processes
The two main functions of receptorsare: ligand (drug) binding, and,activation of effector mechanism
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Under physiologic conditions, receptorfunction is regulated by molecules
supplied by the body
All that drugs can do at receptors ismimic or block the action of bodys
own regulatory molecules
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Drugs cannot give cells new function
but can only alter the rate of pre-existing processes
Drugs produce their therapeuticeffects by helping the body use itspre-existing capacities to the pts best
advantage. Medications simply help
body to help itself
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In theory, it should be possible to
synthesize drugs that can alter rate ofany biologic processes for whichreceptors exist
Ligand binding is determined byaffinityand specificity
Affinity describes how strongly thedrug and receptor interact.
Specificity refers to selectivity areceptor has for a drug.
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Agonists & Antagonists
Agonists bind to receptor sites &activate receptor mechanisms(elicit biological responses).
Antagonists bind to receptors
but do not activate effectormechanisms (do not producebiological effects)
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Effectors
Transduce drug-receptor interactionsinto cellular effects.
1. Intracellular receptors
2. Transmembrane receptors
3. Ligand-gated ion channels
4. Receptors coupled to 2ndmessenger systems
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Individual Variations in Drug
Responses
In order to maximize beneficial drugresponses & minimize harm, we mustadjust therapy to account for sources
of individual variation small pts need smaller doses than
large pts
Dosage adjustments made to accountfor size are often based on bodysurface area, rather than simply onbody weight
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Infants & the elderly are more
sensitive to drugsTherapeutic & adverse effects differ
between males & females
Kidney disease can decrease drugexcretion
Liver disease can reduce drug
metabolism
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When pts become tolerant to a drug,
dosage must be increased to maintainbeneficial effects
Placebo effect is `the component of a
drug response that can be attributedto psychologic factors
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Genetic factorsespecially genetically
determined rates of drug metabolism-can be a source of individual variation
Poor patient compliance is a major
source of individual variation.
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Classification of Drugs
Adrenergic
Dopaminergic
Cholinergic Drugs
Anticholinergic Drugs
Calcium Channel Blockers Ace Inhibitors
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Angiotensin II Inhibitors
Opioids analgesics Proton Pump Inhibitors
Corticosteroids
Steroids