Therapeutic window is a range of doses that produces therapeutic response without causing any significant adverse effect in patients.
Generally therapeutic window is a ratio between minimum effective concentrations (MEC) to the minimum toxic concentration (MTC). The levels of drug should always be between MEC and MTC in order to provide risk free therapeutic effects. If any drug crosses MTC then it will surely elicit toxic effects and if drug is unable to surpass MEC then it will cause therapeutic failure. MEC is also called as minimum inhibitory concentration (MIC).
Therapeutic window is also termed as safety window and can be quantified by therapeutic index.
Therapeutic Index (TI):
Therapeutic index (TI) describes a relationship between the doses of a drug that causes lethal or toxic effects with the dose that causes therapeutic effects. It is also called as therapeutic ratio.
Mathematically you can calculate TI by following way;
Therapeutic Index: LD50/ED50
Therapeutic Index: TD50/ED50
LD50 is the minimum amount of drug that causes adverse effects in 50% of the population. LD50 could also be replaced with Toxic dose (TD50)
ED50 is the quantity of a drug that can produce desired therapeutic effects in 50% of the population. Such types of studies are usually conducted in animal models.
Ideally any drug that requires more amount to produce toxic or adverse effects in 50% of population will have wider therapeutic index and vice versa. Drugs having wider therapeutic index are safer in comparison to those having low therapeutic index because minor modification in the dose of such drugs (aspirin, acetaminophen) will not produce toxic effects.
For examples NSAIDs have wider therapeutic index and warfarin has narrow therapeutic index as it has therapeutic index less than two.
Examples of Drugs:
Here is a list of some common potent drugs having low therapeutic index;
- Amphotericin B
- Craig, C. Modern Pharmacology With Clinical Applications. 6th ed. LWW, 2003
- Katzung, B. Basic and Clinical Pharmacology. 11th ed. McGraw Hill Medical, 2009
- Golan, D. “Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy”. 2nd ed. LWW, 2008.
- David E. Golan, Armen H. Tashjian, Ehrin J. Armstron. Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. Pharmcodynamics, Chapter 02. P. 25-26
- Coleman, Michael D. (2010). Human Drug Metabolism: An Introduction. John Wiley & Sons. p. 01
Copyright 2012 Medimoon.com. All rights reserved. No part of this site can be reproduced without our written permission.