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### 15 Cards in this Set

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 What is selectivity? Selectivity is the property of a receptor resulting from the highly structured binding site that allows it to bind to a limited variety of ligands. What is specificity? Specificity is the property of a drug that makes it able to bind only to a limited range of receptors, and gives it a higher affinity for its chosen receptor. What is K(D)? K(D) is the equilibrium dissociation constant of the drug for the receptor. It is the result of dividing the dissociation constant by the association constant, and is the amount of drug necessary to occupy one-half of the receptor population. K(D) is the number used to quantitate the degree of affinity between a drug and receptor, because K(D) is inversely proportional to affinity. What is a log dose-response curve? A LDR curve is a plot with % receptor occupancy on the Y-axis (or amount of response) and a log scale of drug dose (or drug concentration) on the X-axis. The semi-log plot produces a sigmoidal curve. What is the difference between a graded LDR curve and a quantal LDR curve? A graded LDR plot, the response can be measured at any level between the max and min. In a quantal LDR plot, the response is either all-or-nothing, and the Y-axis usually represents a cumulative or % cumulative response. What is the equation for level of response as a function of drug level? The fractional response is given by: 1/ [1+(K(D)/D)] What are the 5 assumptions made for the fractional response equation? 1. each individual drug-receptor interaction produces the same level of response 2. individual activations are additive 3. max effect occurs when every receptor site is occupied 4. D-R complex is a readily reversible reaction 5. occupation of one receptor by drug doesn't affect binding to other receptors What is the EC50 (or ED50)? The EC50 is the concentration of drug (and ED50 is the dose of drug) that provides one-half the max possible effect for that drug. It should be equal to the K(D) for that drug. What is potency? Potency is the amount of drug necessary to produce a given amount of response. It is communicated via the EC50 (or ED50), the amount of drug needed for half-maximal response, and the further to the left the LDR curve is on the plot, the more potent the drug. Note the potency refers to an AMOUNT OF DRUG. What is efficacy? Efficacy is the maximal level of response achievable with the drug. The term is interchangable with "intrinsic activity." Note that efficacy refers to an AMOUNT OF RESPONSE. What is the Theraputic Index? The Theraputic Index (T.I.) is the ratio of LD50 to ED50, or the dose needed to produce a lethal or toxic effect in 50% of individuals over the dose needed to produce 50% of the max effect. The larger the T.I., the safer the drug. What is the best way to determine the affinity of an antagonist for its receptor? To find the affinity of the antagonist for its receptor, it is best to determine the amount of antagonist that causes a two-fold decrease in potency (a right-shift) of the agonist on a response. This indicates the amount of antagonist at which one-half of the receptors are occupied by the antagonist. The value of this is called K(A). What is the Schild plot? The Schild plot is the way to graphically determine is pA2 of an antagonist. The Y-axis has the Log[(Dx/Do)-1], where Dx is the EC50 of the agonist in the presence of the antagonist, and Do is the EC50 of the agonist by itself. The X-axis has the Log[concentration of antagonist]. Where the resultant line hits zero on the Y-axis (Dx/Do =2) is the K(A), and -Log(K(A))=pA2. What is receptor subsensitivity? Receptor subsensitivity refers to the the progressive loss of effectiveness of drugs after continual usage. It is also called desensitization, and possible causes include reduced numbers of receptors or less effective receptor-second messenger system coupling. What is receptor supersensitivity? Receptor supersensitivity occurs when continual presence of an antagonist causes the tissue to compensate for lack of stimulation by increasing its receptor sensitivity. In these cases, application of the agonist (or removal of the antagonist) causes an abrupt disproportionate increase in response.