What are drug-drug interactions?
In the broadest sense, a drug interaction occurs whenever one drug affects the pharmacokinetics, pharmacodynamics, efficacy, or toxicity of another drug. The two drugs need not physically interact with each other to produce the effect. When the drug combination results in an undesired effect, the drug interaction becomes an adverse drug interaction. Drug interactions are much more common than adverse drug interactions.
Should we be concerned about drug interactions?
Drug-drug interactions are of potential concern whenever a person takes two or more medications concurrently. Indeed, in a recent poll adults were asked what they would be very concerned about if they were to check into a hospital or other health care facility. The number one concern (61%) was being given the wrong medicine, but a close second at 58% was a negative interaction between multiple drugs.
How often do adverse drug interactions occur?
It has been estimated that adverse drug outcomes occur about once every 100 patient days. These adverse events are costly and often preventable. Drug interactions produce asymptomatic alterations in drug response on a regular basis. Occasionally drug interactions result in obvious adverse outcomes. A study of 1000 older patients admitted to a hospital geriatrics unit identified 894 patients who were receiving two or more drugs. Although a majority of these patients were receiving potentially interacting drug combinations (60% of the patients), only about 15% of them had symptoms of an adverse drug interaction on admission. It is important to remember that these adverse drug interactions are predictable and, therefore, preventable. Combinations of interacting drugs are sometimes used intentionally with favorable effectfor example in patients with hypertension or neoplastic diseases.
About the Authors
Drs. Philip Hansten and John Horn are recognized international authorities in the field of drug-drug interactions and have more than 75 years of combined experience in the field. The drug interactions books by Dr. Hansten and Dr. Horn have been translated into 6 languages and have sold more than one million copies worldwide since 1971. The authors have lectured extensively in North America, as well as in more than two-dozen countries throughout the world.
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