Multiple Drug Interactions


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 effec