Stockley, the recognised authority on interactions gives a more succinct definition in the 9th edition -

‘A drug interaction is said to occur when the effects of one drug are changed by the presence of another drug, herbal medicine, food, drink or by some other environmental chemical agent’

Where do you go for information on drug interactions?

Using the BNF as a guide

Whether you use the electronic version of the BNF, an APP on your phone or the hard copy, the place to look for drug interactions is Appendix 1 of the BNF. The introduction to Appendix 1 is both useful and informative. Many of the appendices of the BNF have changed over the years but Appendix 1 remains the section to look for information on drug interactions.

What are the main types of drug interactions?

The main types of drug interaction are pharmacokinetic in that the two drugs can affect absorption, distribution, metabolism or excretion. In the less common pharmacodynamic interactions, a second drug can affect the way the first drug acts on receptors for example. The most common, clinically significant pharmacokinetic drug interactions relate to metabolism. In this ebook we will not be going into the exact mechanisms of the interactions but some pharmacology is required to understand how these interactions may happen and how they may be avoided.