Pharmacokinetics in Everyday Clinical Practice E-Book

Federico Pea

• Herausgeber: SEEd Edizioni Scientifiche
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2012

Beschreibung

This book provides a practical introduction to the main concepts of pharmacokinetics and how they can be applied in clinical settings, without using complicated mathematical equations. Essential information on approaches to drug-dosing and monitoring in special populations, including patients with renal and hepatic diseases and elderly patients, are given. Charts, illustrations and examples of calculations are added to clarify concepts and terminology of pharmacokinetics. It’s a guide for students and clinicians who want clear, useful guidance to the basic principles of pharmacokinetics and their application into clinical practice.

Leseprobe

Pharmacokinetics in Everyday Clinical Practice

Federico Pea

Colophon

© SEEd srl

Piazza Carlo Emanuele II, 19 – 10123 Torino – Italy Tel. [phone] – Fax [email protected]

First edition March 2011 ISBN 978-88-9741-918-1

Although the information about medication given in this book has been carefully checked, the author and publisher accept no liability for the accuracy of this information. In every individual case the user must check such information by consulting the relevant literature.

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the Italian Copyright Law in its current version, and permission for use must always be obtained from SEEd Medical Publishers Srl. Violations are liable to prosecution under the Italian Copyright Law.

Introduction

Pharmacokinetics is a branch of pharmacology that studies the velocity of the processes that determine the course of the plasma concentration of a drug. By applying a series of mathematical models, it enables to quantitatively describe the movement of a drug in the body over time. This is the result of the various phases that occur after administration of a drug, i.e., absorption, distribution, metabolism and excretion. Knowing the “fate” of a drug in the body is the prerequisite for defining the most appropriate dosing regimen, in terms of amount and frequency of administration, in order to obtain the desired therapeutic effect. In fact, the therapeutic effect of a drug depends on the achievement of effective concentrations in target tissues. As an example, we can imagine what might be the fate of a drug after oral administration (Figure 1).

Figure 1. Fate of a drug after oral administration.

After being ingested, and having reached the gastrointestinal system, the drug, if it has suitable physicochemical characteristics, is absorbed and eventually enters the bloodstream. At this level, the drug binds to plasma proteins (in most cases with albumin), to a different degree depending on the circumstances, and then is distributed to various organs and tissues. Only the free moiety of the drug is “biologically active,” which means that only the unbound fraction can diffuse out of the bloodstream to be distributed through the tissues. After this, in order to be eliminated, the drug must pass through the emunctory organs, in which it may or may not undergo biotransformation (metabolism), and is then excreted, as appropriate, by the kidney, or gut, or via other minor pathways (e.g., exhaled air, sweat, etc.).

In this scenario, plasma essentially represents the mean by which the drug is conveyed to the various districts within the body. For this reason, knowing the plasma concentration profile of a drug in relation to the time after its administration can be a useful tool for understanding its pharmacokinetic behavior in the body (Figure 2).

Figure 2. Plasma concentration versus time curve.

The aim of this publication is not to define the strict mathematical rules that are the basis for pharmacokinetic studies conducted by experts, but to help all physicians to become familiar with some concepts that will enable them to apply the principles of pharmacokinetics in the daily management of their patients’ treatments. Therefore, unlike in specialized texts, the use of mathematical formulas will be minimal, serving only to help physicians to understand these concepts.

1 Pharmacokinetics and Terminology

The usefulness of pharmacokinetics in the daily management of therapy can be more easily understood by defining and explaining the major pharmacokinetic parameters, as summarized in Table I.

Pharmacokinetic parameter

Abbreviation

Oral bioavailability

Fos

Volume of distribution

Vd

Plasma clearance

CL

Plasma elimination half-life