Inconsistencies of absolute drug-drug contraindication reports: Analysis of Summaries of Product Characteristics of commonly prescribed drugs.

AIMS: Prescribing information should follow a defined structure to help prescribers easily find required information. Often information appears in different sections of Summaries of Product Characteristics (SmPCs) in an inconsistent way. Still unknown is how this inconsistency affects absolute contraindications and how it can be improved. Thisstudy aimed to evaluate the structure of absolute contraindications in SmPCs based on absolute drug-drug contraindications (DDCI) in the section 'contraindications' and references to sections 'special warnings and precautions for use' (here as 'warnings') and 'interaction with other medicinal products and other forms of interaction' (here as 'interactions'). METHODS: SmPCs of 693 commonly prescribed drugs were analysed regarding absolute DDCI in 'contraindications' sections. References to sections on 'warnings' and 'interactions' were evaluated to characterize information provided about DDCI. RESULTS: Of 693 analysed SmPCs, 138 (19.9%) contained ≥1 absolute DDCI. Of 178 SmPCs that referred to sections on 'warnings' or 'interactions', 131 (73.6%) did not contain further information on absolute DDCI, whereas 47 (26.4%) did. Such additional information was found in sections on 'interactions' and 'warnings' in 41 (87.2%) and 9 (19.1%) SmPCs, respectively. CONCLUSIONS: Information regarding absolute DDCI was found not only in sections on 'contraindications' but also in sections on 'warnings' and 'interactions'. Information was not given with consistently straightforward phrasing and structure and so can leave uncertainty for prescribers. To improve drug safety, clear definitions and wording for absolute and relative contraindications should be provided, ideally in tables.