Biotransformation clearance equations

To account for all the administered drugs in the urine when the drug is administered intravenously often is not possible. This may be caused by the excretion of some of the drug via an extrarenal route, excretion of a metabolite via an extrarenal route, further biotransformation of primary metabolite into chemical forms that are not identified by the analytical method used, or formation of unknown and unidentified primary metabolites. If the total amount of metabolites can be identified in the urine, then one can determine the metabolite clearance using the following equation ... 

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