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BMS263

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Term
Definition
Drug   A chemical substance of known structure, other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Sourced from microorganisms, plants, human cells and animals, minerals and labs  
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Exogenous   Made outside the body  
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Endogenous   Made by the body itself  
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Pharmacodynamics   How a drug affects the body (it's mechanism of action)  
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Pharmacokinetics   How the body affects the drug. E.g. how the body absorbs, transports, metabolises & excretes the drug. It will affect drug action by determining which tissues the drug gets exposed to etc.  
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General Principal of Drug Action   Requires non-uniform distribution of the drug molecule within the body or tissue. Molecules must bind with particular constituents of cells and tissue to produce effect. Also involves potency and effacacy  
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Potency   How much of the drug is required to produce a response. Determined by affinity & efficacy of drug. Compared by considering the EC50. Drugs of high amount have higher affinity for receptors & occupy proportion of receptor even at low concentrations  
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EC50   Concentration at which the drug produces 50% of its maximal response (Effective concentration at 50%)  
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Efficacy   The ability of a drug to produce its biological response  
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Drug Targets   Most are proteins. E.g. receptors (Acetylcholine receptor on muscular junction), Enzymes (Acetylcholine esterase), Carrier molecules (for sugar and amino acids) & Ion channels  
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Drug Specificity   Describes the number of effects the drug produces. Acts selectively on particular cells and tissues and shows a high degree of binding site specificity. It is reciprocal  
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Selectivity   Describes the number of molecular targets that the drug interacts with  
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Agonist   Activates a receptor. Takes place of endogenous substance. There are full and partial types. Possesses significant efficacy  
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Antagonist   A drug binds to the receptor without causing activation and prevents an agonist from binding. Has zero efficacy. Can be reversible or irreversible  
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Affinity   The strength of the interaction between a drug and its molecular target  
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Efficacy   How big an effect the drug will have’ when all targets (receptors) are occupied. Describes the tendency of the drug-receptor complex to adopt the active rather than the resting state. The difference between full and partial agonists  
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Full Agonist   Induce maximal response when all receptors are occupied (high efficacy)  
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Partial Agonist   Have some efficacy but are unable to generate a maximal tissue response. Drugs with intermediate levels of efficacy, such that even when 100% of the receptor are occupied the tissue response is sub-maximal  
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Activation   The receptor is affected by the bound molecule in such a way as to elicit a tissue response  
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Drug Desensitisation/ Tachyphylaxis   Drug effect gradually diminishes when given continuously/ repeatedly. Develops in course of minutes. Caused by change in or translocation of receptors, exhausted mediators,increased metabolic degradation, active extrusion from cells & physiological adapt  
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Tolerance   More gradual decrease in responsiveness to a drug, taking weeks or days to develop  
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Refractoriness   The loss of the therapeutic efficacy  
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Drug Resistance   The loss of the effectiveness of antimicrobial or anti-tumour drugs  
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Change in Receptors   In regards to desensitisation. A conformation change that inhibits the efficacy of the drug. E.g. agonist binds but can no longer activate it (type 2 diabetes)  
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Translocation of Receptors   In regards to desensitisation. Receptors are internalised such that the availability of the receptors is decreased. i.e. There are less receptors for the drug to bind to. E.g. A decrease in b-adrenergic receptors can occur  
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Exhaustion of Mediators   In regards to desensitisation. Depletion of substances required for a drug response. E.g. Amphetamines cause the release of amines from neurons. Once there is a depletion of amine stores, these drugs have decreased potency  
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Increased Metabolic Degradation   In regards to desensitisation. Body produces more enzymes that catalyse the chemical degradation of drug. Usually induction of hepatic drug metabolising enzymes  
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Active Extrusion of Drug   In regards to desensitisation. Some drugs need to enter target cells to have an effect. If the target cells expel the drug, a lower intracellular concentration of the drug will occur, decreasing its potency. e.g. Cancer chemotherapy  
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Physiological Adaptation   Readjustment of homeostatic mechanisms occur to compensate for drug action. E.g. Thiazide diuretics increase production of urine, decrease BV &BP. Activation of renin-angiotensin 2 system can occur stimulating physiological mechanisms to increase BP again  
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Pharmacogenetics   The study of how genetic variability affects the response to drugs  
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Individual Response To Drugs   Inherited genes can alter drug response. Can alter pharmacodynamics and pharmacokinetics. A persons environment & stage of life can alter drug responses. Also nutrition, use of other drugs, allergic reactions & idiosyncratic reactions  
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Drug Agonism   One drug can increase the activity and/or unwanted effects of another drug. - e.g. The degradation and clearance of two drugs may involve the same enzyme  
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Drug Antagonism   One drug can decrease the activity of another drug. Four main types: Chemical antagonism, Pharmacokinetic antagonism, Block of receptor or block of receptor-effector linkage (competitive vs non-competitive), & Physiological antagonism  
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Chemical Antagonism   Refers to the uncommon situation where the two substances combine in solution; as a result, the effect of the active drug is lost. Example: The use of chelating agents (dimercaprol) that binds to heavy metals and thus reduce their toxicity  
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Pharmacokinetic Antagonism   The antagonist effectively reduces the concentration of the active drug at its site of action. The rate of metabolic degradation of the active drug may be increased  
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Competitive Antagonist   Drug binds selectively to a particular receptor without activating it, but in such a way as to prevent binding of the agonist. Can be reversible (Reversible bonds with receptor) or irreversible (Antagonist dissociates slowly or not at all from receptor)  
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Non-Competitive Antagonist   Antagonist and agonist bind to receptor at different sites, or one drug inhibits the activity of the other drug by altering cell signalling down-stream of the receptor. Antagonist blocks the chain of events that lead to a response by action of agonist  
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Physiological Antagonism   Refers to the interaction of two drugs whose opposing actions in the body tend to cancel each other. The two drugs act on separate mechanisms  
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