This study showed that high-income countries had the highest ADR reporting rates and low-income countries the lowest, with large variations across countries in each group. Significant differences in ADR reporting rates were only found for ADRs of the type 'skin and subcutaneous tissue disorders' and for the therapeutic groups 'antiinfectives for systemic use' and 'antineoplastic and immunomodulation agents'. To strengthen ADR reporting rates, especially in low-income countries, more research is needed about the impact of organizational structures and economic resources of national pharmacovigilance centres and ADR reporting practices on the large variations in ADR reporting rates within income groups.
Case reports from the WHO ADR database, including index cases involving four out of five PPIs, along with evidence of a possible mechanism, provide compelling evidence that there is a causal association between members of the PPI drug class and myopathy including polymyositis. Evidence was also obtained to support the view that PPI use may be associated with occurrence of other myopathies, including the serious reaction rhabdomyolysis.
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT
• Rhabdomyolysis is a serious but rare adverse effect of statins.
• The mechanism of rhabdomyolysis with statins is poorly defined, but the occurrence is known to increase with dose/ concentration.
• Some macrolides are known to interact with statins; however, azithromycin has not been described to interact with statins with the exception of two literature case reports.
WHAT THIS STUDY ADDS
• A case series in the World Health Organization Adverse Drug Reaction (WHO‐ADR) database was suggestive of a possible drug interaction between statins and azithromycin with rhabdomyolysis.
• A disproportionality measure, Omega, was shown to identify previously not recognized suspected drug interactions within the WHO‐ADR dataset.
AIMS
In a systematic screening of the World Health Organization Adverse Drug Reaction database, VigiBase, in July 2008, a measure of association used to detect interactions (Omega) highlighted azithromycin with the individual statins atorvastatin, lovastatin and simvastatin and rhabdomyolysis. The aim was to examine all reports including rhabdomyolysis‐azithromycin and statins in VigiBase to assess if the data were suggestive of an interaction.
METHODS
The individual case reports in VigiBase and the original files were reviewed. In order to investigate the reporting over time for rhabdomyolysis with azithromycin and statins to VigiBase, Omega values were generated retrospectively.
RESULTS
The reporting over time showed that rhabdomyolysis under concomitant use of azithromycin and statins was reported more often than expected from 2000 and onwards in Vigibase. After exclusion of possible duplicates and follow‐up reports, 53 cases from five countries remained. Rhabdomyolysis occurred shortly after initiation of azithromycin in 23% of cases. In 11 patients an interaction had been suggested by the reporter. With the exception of one patient, the statin doses reported were within the recommended daily doses.
CONCLUSIONS
Case reports in VigiBase are suggestive that interactions between azithromycin and statins resulting in rhabdomyolysis may occur. This analysis showed the potential of the newly developed disproportionality measure, Omega, which can help to identify drug interactions in VigiBase in the future. The results also showed that reviewing spontaneous reports can add information to drug interactions not established previously.
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