Drug interactions
BMJ 2001; 323 doi: https://doi.org/10.1136/sbmj.0109323 (Published 01 September 2001) Cite this as: BMJ 2001;323:0109323
- Oliver Jones, clinical lecturer in pharmacology1
- 1University of Oxford
Drug interactions are common. It is important to be aware which drugs are likely to interact. Many easily accessible references exist, such as appendix 1 of the British National Formulary, but it is not practicable to consult these every time you write a prescription. Knowledge of a severe drug interaction should deter you from using the combination of treatments. However, in other circumstances, only closer clinical management or adjustment of dose is indicated. Furthermore, drug interactions may even be used therapeutically, as in the treatment of poisoning. This article describes the principles of drug interactions, their identification, and their management.
Types of drug interactions
There may be two outcomes of drug interaction. Antagonism occurs when the action of one drug opposes that of another, while synergism occurs when the effects of coadministration of drugs is additive. When the sum of two drugs is more than a simple additive effect, this is known as “potentiation.” Not all drug interactions are harmful. For example, the ISIS-2 study showed that aspirin and streptokinase each improve outcome in myocardial infarction, and that the combination of both these drugs has an additive …
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