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. 2008 Feb 14;2:21–39.

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© 2009 The authors.

This article is published under the Creative Commons Attribution By licence. For further information go to: http://creativecommons.org/licenses/by/3.0.

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Pharmacokinetic paramaters. A drug is absorbed to the systemic circulation, where the drug may be bound to plasma proteins or distributed throughout body tissues (fat or fluid). It is only the free fraction of the drug in plasma that can exert an effect. From the systemic circulation the drug is transported to its site of action to exert its pharmacodynamic effect. The drug is undergoing elimination via biotransformation through metabolic pathways and elimination (often through liver, kidneys and faeces). The block arrows point to modifications in efficacy by pharmacodynamic (mechanism of action) factors, and tolerability by modifications of pharmacokinetic parameters.