Term
| Dissociation constant equation |
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Definition
Kd = [L][R] / [LR]
L = ligand, R = receptor |
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Term
| Dissociation constant definition |
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Definition
| Kd is the ligand concentration at which half the receptors are occupied. Thus, low Kd means higher affinity. Note that if two drugs have the same mechanism of effect on the receptor but different Kd, they will both reach saturation, but at different concentrations. |
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Term
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Definition
| Concentration at which half the maximal effect is obtained. Similar to Kd, but directly measures effect instead of receptor binding. |
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Term
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Definition
| The maximum effect a drug can have on its target, i.e. the magnitude of Emax. |
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Term
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Definition
| A measure of how much of a drug is needed to achieve its effect, i.e. the magnitude of EC50 where a lower value means a more potent drug. |
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Term
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Definition
| Binds reversibly to active site but has zero efficacy. Reduces natural ligand potency but has no effect on efficacy. |
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Term
| Noncompetitive antagonist |
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Definition
| Either binds irreversibly to the active site or reversibly to an allosteric site. Reduces efficacy of the natural ligand, but has no effect on potency (the concentration at which half-max effect is achieved is the same, but the effect itself is lower) |
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Term
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Definition
| Ligand that binds at the active site competitively but has lower efficacy than full agonists. Appears to be a competitive antagonist at low concentrations, but at high concentrations will reduce the apparent efficacy to that of the partial agonist, a "built-in safety margin". |
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Term
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Definition
| Binds to and inhibits a receptor that has constitutive activity when unbound. Differentiate from antagonism. Has little use in pharm so far. |
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Term
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Definition
| In some cases for maximal effect not all receptors need to be bound (EC50 < Kd). Usually this is because signalling mechanisms have inherent amplification, for example when a GPCR activates adenylyl cyclase it produces many molecules of cAMP for only one molecule of enzyme. |
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Term
| Quantal dose-response relationships |
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Definition
| Measuring drug effectiveness by determining number of subjects that achieve a specific criterion. Because this is a yes/no definition, it is said to be quantal. |
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Term
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Definition
| Median effective dose to produce therapeutic effect. (i.e. half of subjects show response at this dose) |
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Term
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Definition
| Median dose to produce toxicity. |
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Term
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Definition
| Median dose (estimated) to kill subjects. |
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Term
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Definition
| TD50 / ED50, where a larger number indicates a safer window. |
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Term
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Definition
| LD1 / ED99, the dose that would kill 1% of the population over the dose that would help the entire population. Bigger is better. |
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