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Occupation

Signal transduction

By dividing these factors into two groups, pharmacologists have reconstructed a picture of drug response that is somewhat idealized but more accessible to analysis. Pharmacokinetic factors include the absorption, distribution, metabolism, and excretion of drugs and determine the time course of drug disposition, while pharmacodynamic factors are receptor mediated and determine the response.

Drug response = ^ pharmacokinetics + ^ pharmacodynamics

Absorption Receptor mediated

Distribution Metabolism Excretion

Because the free drug concentration in tissue water bathing drug-receptor (DR) complexes is in rapid equilibrium with plasma water, changes in the concentration of DR complexes, and hence response, parallel changes in plasma drug concentration as schematized in the following diagram.

Pharmacokinetics

Pharmacodynamics t

[D] plasma

♦ [D] -► [DR]

t

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