Expanded Answers for Study Problems in: Rowland & Tozer's Clinical Pharmacokinetics: Concepts and Applications

Chapter 2 - Basic Considerations

Study Problems on Page 17

1. Define the following terms:

Pharmacokinetics: The study of the absorption, distribution, metabolism and elimination of xenobiotics. This often, but not always, involves a quantitative assessment of xenobiotic disposition. While one can refer to pharmacokinetics as the study of what the body does to a xenobiotic, this is not a definition!

Metabolism: Defining metabolism as the "irreversible conversion to another chemical species" does not adequately define what is meant by metabolism. Metabolism is better defined as the enzyme-mediated chemical conversion of xenobiotics to another species. This specifies that were are referring to an enzyme-mediated process, excluding chemical degradation. Moreover, some metabolic pathways are reversible ... potentially, with the same enzyme catalyzing both reactions (formation of metabolite and conversion of metabolite back to the parent compound)!

Compartment: Importantly, a compartment does not indicate an anatomical location of a xenobiotic, it identifies the kinetic characteristics of the space in which the xenobiotic is distributed (which may actually represent numerous tissues).

3. The question assumes that the assay does not discriminate between drug and inactive metabolite. For example, suppose a blood sample contained 2 mg/L of parent drug and 1 mg/L of inactive metabolite. A non-specific assay would provide a measurement of 3 mg/L for the parent drug. Hence, only a portion of the measured concentration at any time represents active drug.

Return to Pharmacokinetics and Biopharmaceutics Homepage

Return to Expanded Answers for Study Problems Index Page