Table 1.

Categories used to classify drug interactions in the four compendia

Vidal

There are four levels of seriousness that are based on the clinical management which is recommended: ‘contraindication’ (absolute), ‘avoid’ (relative contraindication), ‘precaution for use’ (combination possible if recommendations are followed), and ‘to take into account’ (no specific recommendation).

BNF

BNF uses a bullet to mark interactions that are potentially hazardous and where combined administration of the drugs involved should be avoided (or only undertaken with caution and appropriate monitoring). BNF may also state specifically whether a drug combination must be avoided or whether a drug combination is contraindicated by the manufacturer.

DIF

DIF classifies the severity of drug interactions into three categories (major, moderate and minor) and the documentation level in five categories (established, probable, suspected, possible and unlikely). A significance rating from 1 to 5 is assigned to each drug interaction based on the severity and the documentation gradings: 1 (major severity and documentation suspected or more), 2 (moderate severity and documentation suspected or more), 3 (minor severity and documentation suspected or more), 4 (major or moderate severity and documentation possible), 5 (minor severity and documentation possible or any severity and documentation unlikely).

Micromedex

Micromedex classifies the severity of drug interactions into three categories (major, moderate and minor) and the documentation level in five categories (excellent, good, fair, poor and unlikely). There is no overall significance rating.