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A large proportion of potential drug interactions are known from pre-authorization studies, but adverse drug reactions (ADRs) due to interactions (adverse drug interactions) are often first detected through astute observation in clinical practice. Individual case safety reports (ICSRs) are collected from broad patient populations and allow for the identification of groups of similar reports. Systematic screening for adverse drug interactions in ICSRs will require an understanding of which information on these reports can be suggestive of adverse drug interactions.The aim of the study was to identify what reported information may support the identification of drug interaction safety signals in collections of ICSRs.Three previously published safety signals of suspected adverse drug interactions were re-evaluated. To this end, 137 reports related to these signals were retrieved from the WHO Global ICSR Database, VigiBase™, and corresponding original reports were obtained from national pharmacovigilance centres. Criteria from an operational score for causality analysis of drug interactions of clinical cases, the Drug Interaction Probability Scale (DIPS), were applied to each of these reports with the aim of identifying what supportive information tends to be available in ICSRs. For three DIPS elements (plausible time course, resolution of the ADR after terminating the drug inducing the interaction without changes in affected drug therapy (positive dechallenge) and alternative causes of the reaction) we also compared the amount of information in VigiBase™ and in original reports, and in free text and structured data.Commonly fulfilled DIPS elements on reports supporting an adverse drug interaction signal were plausible time course (50 reports; 36%) and positive dechallenge (8 reports; 6%). Alternative causes for the observed adverse reaction were observed in 72 (53%) reports. We found limited differences between VigiBase™ and original reports for the structured data, although a substantial amount of additional information was available in free text in original reports.Information on plausible time courses and resolution of the adverse reaction upon withdrawal of the drug suspected to have induced the interaction may be a useful element in identifying suspected adverse drug interactions from ICSRs. Of these, plausible time course is by far the most commonly reported element in the three signals studied here. Our analysis also demonstrated the importance of sharing and analysing information available in free text where relevant clinical details are often available, such as those mentioned above, along with severity and dosage changes.

Adverse drug interaction surveillance in collections of Individual Case Safety Reports (ICSRs) remains underdeveloped. Most efforts to date have focused on disproportionality analysis, but the empirical support for its value is based on isolated examples. Additionally, too little attention has been given to the potential value of the detailed content of ICSRs for improved adverse drug interaction surveillance.The aim of the study was to identify reporting patterns indicative of suspected adverse drug interactions before the drug interactions are generally established.A reference set of known adverse drug interactions and drug pairs not known to interact was constructed from information added to Stockley's Drug Interactions Alerts between the first quarter of 2007 and the third quarter of 2009. The reference set was used to systematically study differences in reporting patterns between adverse drug interactions before they are generally established and adverse drug reactions (ADRs) to drug pairs that are not known to interact, in the WHO Global ICSR Database, VigiBase. The scope of the study included pharmacological properties such as common cytochrome P450 metabolism, explicit suspicions of drug interactions as noted by the reporter, clinical details such as dose and treatment overlap, and the lower limit of the 95% credibility interval of a three-way measure of disproportionality, Omega(025) (Ω(025)), based on the total number of reports on two drugs and one ADR together. Analyses were carried out including and excluding concomitant medicines.Five reporting patterns were highlighted as particularly strong indicators of adverse drug interactions before they are known: suspicion of interactions as noted by the reporter in a case narrative, the assignment of the two drugs as interacting or through an ADR term; co-reporting of effect increased with the drug pair; and, finally, an excess total number of reports on the ADR together with the two drugs, as measured by Ω(025). Overall, the inclusion of concomitant medicines led to a larger number of true adverse drug interactions being highlighted, but at a substantial decrease in the strength of most indicators. Notably, the inclusion of concomitant medicines completely eliminated the value of Ω(025) as an indicator of adverse drug interactions, in this systematic evaluation.Reported suspicion of interactions as noted by the reporter in a case narrative, the assignment of the two drugs as interacting or through an ADR term; co-reporting of effect increased with the drug pair and by the Ω(025) each provide unique information to highlight adverse drug interactions before they become known in the literature. To our knowledge, this is the first systematic analysis demonstrating the value of disproportionality analysis for adverse drug interactions using a comprehensive reference set, and the first study to consider a broader basis including clinical information for systematic drug interaction surveillance.

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.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.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.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.

Polymyositis occurring in patients treated with omeprazole has been signalled as a possible adverse drug reaction (ADR) by the New Zealand Intensive Medicines Monitoring Programme (IMMP) and the WHO Collaborating Centre for International Drug Monitoring: the Uppsala Monitoring Centre (UMC). Polymyositis and other myopathies have also been reported in post-marketing data and in the medical literature in association with proton pump inhibitor (PPI) use. We wished to follow-up these signals and investigate the evidence of causality for the association of polymyositis and other myopathy with PPI use.Spontaneously reported ADRs from national monitoring centres are sent to the WHO ADR database (VigiBase). VigiBase was searched for case reports of the PPIs, omeprazole, pantoprazole, lansoprazole, esomeprazole and rabeprazole, with terms indicative of myopathy, and further information was elicited from the national centres to help establish causality. Literature sources were reviewed for the occurrence of the above terms in combination with PPIs.In total, there were 292 reports of various myopathies with PPIs, excluding 868 cases of 'myalgia'. In this analysis, 69 patients recovered when the drug was withdrawn and, in 15 patients, the reaction re-occurred when the drug was reinstated. In one-third of the 292 cases, the PPI was the single administered drug, and the PPI was the single suspected drug by the reporter in 57% of reports where concomitant medication was used. In this analysis, three index cases are documented. One involves the same patient taking three different PPIs (lansoprazole, esomeprazole and rabeprazole) at different time periods, with myalgia and muscle weakness occurring with all three drugs. In the two other index cases, myopathies with esomeprazole and omeprazole were reported with positive rechallenge, and causality was assessed as 'possible' and 'certain' by the reporting centres. In 27 cases myositis or polymyositis was reported. Other myopathies were reported, including 35 cases with rhabdomyolysis. In 9 of these cases, the PPI was withdrawn and the reaction abated. The PPI was reinstated in one patient, but the reaction did not re-occur. Time to onset was given in 17 of the rhabdomyolysis cases, rhabdomyolysis occurred with the first week in 9 cases, and in 3 cases the reaction occurred between 14 days to 3 months of treatment. In 12 of these patients, an HMG-CoA reductase inhibitor (statin) was taken concomitantly.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.

Spontaneous reporting systems remain the cornerstone of the early detection of previously unknown adverse drug reactions (ADRs) [1]. However, a large proportion of ADRs are known and preventable and they are often due to the coadministration of drugs known to interact [2]. Spontaneous reports of known ADRs can provide insight into the inappropriate co-prescribing of medications. The World Health Organization (WHO) ADR Database (Vigibase) contains more than 3.8 million suspected ADR reports from 82 countries [3]. We examined the coreporting in Vigibase of all drugs classified as ‘established’ and ‘clinically important’ in the Swedish, Finnish, INteraction X-referencing drug–drug interaction database (SFINX database) [4] used in a Swedish patient record system. Thirty-five ‘established and clinically important’ drug–drug interactions (DDIs) were identified. Co-prescribing of these drugs was then searched for in VigiBase. Subsequently, data were retrieved on the severity and evidence for interactions involving these pairs, and actions recommended in Stockley's Interaction Alert [5]. Of those 35 ‘established and clinically important’ drug pairs, 31 were reported in Vigibase, involving 9547 reports from 50 countries. The reported DDIs are listed in Table 1. The serious nature of many of the ADRs listed in Table 1 makes this a major patient safety issue. Also, seven pairs had had only theoretical evidence previously available, and another four pairs had had no previous evidence. Table 1 Clinically important drug–drug interactions Amongst a wide range of drugs, the majority of reports concerned anticonvulsants and anticoagulants. Many of the most reported drug pairs included drugs with narrow therapeutic indexes, such as warfarin, carbamezepine, phenytoin and theophylline. This was further emphasized by the nature of the adverse events reported for the drug pairs: ‘therapeutic level increased’, ‘drug level increased’, ‘drug level decreased’ and ‘therapeutic level decreased’. Spontaneous reports sometimes lack detail, which makes the analysis difficult. For example, risperidone/carbamezepine and convulsions could be due to underlying disease or an overdose effect of risperidone on discontinuation of carbamazepine. In many reports one drug only was reported as ‘suspected’. For example, only 149/661 cases of decreased prothrombin and 197/408 cases of gastrointestinal haemorrhage with warfarin and acetylsalicylic acid were reported as co-suspected or interacting. Judging by attribution of suspicion, it seems that potential interactions were not recognized, although we should not assume that all reports are necessarily results of inappropriate use. The continuing reporting of seemingly well-established interactions strongly suggests insufficient impact of drug information on routine prescribing practices. For example, the US Food and Drug Administration (FDA) has warned of concurrent therapy of rosiglitazone and insulin [6], as it was associated with increased risk of cardiac failure [7]. Since that FDA warning in May 2004, 402 reports of the pair, 52 reports of cardiac failure and 46 reports of the most common symptom, peripheral oedema, have been entered into VigiBase. Studies have shown that education can improve both doctors' and medical students' prescribing patterns [8], and electronic advice can significantly improve recognition of dangerous drug combinations [9]. This review has focused on an analysis of spontaneous reports, with no estimate of drug use. The raw number of reports of combinations should not be interpreted as an estimate of incidence. For some combinations, increased recent reporting might be explicable by increased drug use. Many of the drug pairs have been marketed for several years, and for two-thirds of thepairs reporting started >10 years ago. Our results illustrate a longstanding international problem of comedication of contraindicated drugs. This is in agreement with national studies that have shown that physicians fail to recognize [9] and continue to prescribe contraindicated drugs [10]. We contend that VigiBase and other available data sources could, and should, be utilized to identify preventable ADRs through active screening for potential DDIs. Also, much more effort is needed to communicate patient safety findings appropriately to healthcare providers and patients.

Background: Although systems to collect information about suspected adverse drug reactions (ADRs) were established in many countries and by the WHO in the 1960s, few studies have examined reported ADRs related to national income. Objective: The aim of the study was to characterize ADRs reported to the WHO-ADR database, VigiBase™, and to relate data to national income. Methods: We analysed ADR reports submitted to VigiBase™ from 2000 to 2009 with respect to reporting rate, age and sex of patient, type, seriousness and medications. Reports were also analysed with respect to national income level, classified in accordance with the World Bank definition: low, lower-middle, upper-middle and high. Results: We analysed 1 359067 ADR reports including 3 013 074 ADRs. Overall, 16% of reports were serious and 60% were reported for females. High-income countries had the highest ADR reporting rates (range 3–613 reports/million inhabitants/year) and low-income countries the lowest (range 0–21). Distribution of ADRs across income groups with respect to age group, seriousness and sex was non-significant. Overall, the majority of ADRs were reported for nervous system medications, followed by cardiovascular medicines. Low-income countries reported relatively more ADRs for anti-infectives for systemic use than high-income countries, and high-income countries reported more ADRs for antineoplastic and immunomodulating agents than lower-income groups. Conclusion: 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.

Drug interactions resulting in adverse drug reactions (ADRs) represent a major health problem both for individuals and the community. Despite this, limited information is reported in the literature on the drug interaction categories responsible for causing ADRs. In the study reported here, we investigated the drug combinations most frequently co-reported as interacting in the WHO Global Individual Case Safety Report (ICSR) database, VigiBase, and categorised these according to the drug interaction mechanism. Reports in which drug combinations were co-reported as interacting in at least 20 reports in VigiBase during the past 20 years were included in the study. Each drug combination was reviewed in the literature to identify the mechanism of interaction and subsequently classified as pharmacodynamic and/or pharmacokinetic reaction. Report characteristics were also analysed. A total of 3766 case reports of drug interactions from 47 countries were identified. Of the 123 different drug combinations reported, 113 were described in the literature to interact. The mechanism of the drug interaction was categorised as pharmacodynamic (46 combinations; 41%), pharmacokinetic (28; 25%), a combination of both types (18; 16%) and unidentified (21; 19%). Pharmacodynamic drug interactions primarily concerned pharmacological additive effects, whereas enzyme inhibition was the most frequent pharmacokinetic interaction. The combinations reviewed primarily implicated drugs such as warfarin, heparin, carbamazepine and digoxin. Drug interactions reported in globally collected ADR reports cover both pharmacodynamic, specifically additive pharmacological effects, and pharmacokinetic mechanisms primarily accredited to the inhibition of hepatic cytochrome P450 enzymes. These ADR reports often concern serious threats to patients’ safety and are particularly related to the use of high risk drugs such as warfarin and heparin.