Handbook of Drug Interaction and the Mechanism of Interaction

Copyright © 2011 by Qutaiba A. Ibrahim.

ISBN:                     Softcover                            978-1-4653-0193-2

                               Ebook                                 978-1-4653-0192-5

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DRUG INTERACTION

Is a situation in which a substance affects the activity of a drug, i.e. the effects are increased or decreased, or they produce a new effect that neither produces on its own. Typically, interaction between drugs come to mind (drug-drug interaction). However, interactions may also exist between drugs & foods (drug-food interactions), as well as drugs & herbs (drug-herb interactions). These may occur out of accidental misuse or due to lack of knowledge about the active ingredients involved in the relevant substances.

CLINICAL IMPORTANCE OF DRUG INTERACTIONS

Clinically important adverse drug interactions become likely with the following:

•   Drugs that have a steep dose-response curve and a small therapeutic index, so that relatively small quantitative changes at the target site, e.g. receptor or enzyme, will lead to substantial changes in effect, as with digoxin or lithium

•   Drugs that are known enzyme inducers or inhibitors.

•   Drugs that are exhibit saturable metabolism (zero-order kinetics), when small interference with kinetics may lead to large alteration of plasma concentration, e.g. phenytoin, theophylline

•   Drugs that are used long-term, where precise plasma concentrations are required, e.g. oral contraceptives, antiepilepsy drugs, cardiac antiarrhythmia drugs, lithium

•   When drugs that may interact are used to treat the same disease, for this increases their chance of being given concurrently, e.g. theophylline and salbutamol given for asthma may cause cardiac arrhythmia

•   In severely ill patients, for