How does the BNF decide which drug interactions to include and what criteria are used for determining their clinical significance?
Interactions in the BNF are based on the Summary of Product Characteristics (SPCs), the medical literature and expert advice. The SPCs sometimes include ‘theoretical interactions’, not actually studied but predicted from knowledge of the cytochrome P450 isoenzymes involved in the drug’s metabolism, the BNF does not usually add such theoretical interactions (unless the manufacturer contra-indicates a particular combination). As for the significance of drug interactions, those that are potentially hazardous are shown in bold type on a red background, (a ‘black spot’ is used in the printed version of the BNF to denote a potentially hazardous interaction). It is not possible to define a type of interaction that will always be designated ‘potentially hazardous’. For example, increased plasma concentration of one drug by another may be significant for a drug with a narrow therapeutic index, such as ciclosporin, but much less important for some other drugs. Interactions involving anticoagulan
