Applying two approaches to detect unmeasured confounding due to time-varying variables in a self-controlled risk interval design evaluating COVID-19 vaccine safety signals, using myocarditis as a case example.

We test the robustness of the self-controlled risk interval (SCRI) design in a setting where time between doses may introduce time-varying confounding, using both negative control outcomes (NCOs) and quantitative bias analysis (QBA). All vaccinated cases identified from 5 European databases between 1 September 2020 and end of data availability were included. Exposures were doses 1-3 of the Pfizer, Moderna, AstraZeneca, and Janssen COVID-19 vaccines; outcomes were myocarditis and otitis externa (NCO). The SCRI used a 60-day control window and dose-specific 28-day risk windows, stratified by vaccine brand and adjusted for calendar time. The QBA included two scenarios: (i) baseline probability of the confounder was higher in the control window and (ii) vice versa. The NCO was not associated with any of the COVID-19 vaccine types or doses except Moderna dose 1 (IRR = 1.09, 95%CI 1.01-1.09). The QBA suggested even the strongest literature-reported confounder (COVID-19; RRmyocarditis = 18.3) could only explain away part of the observed effect from IRR = 3 to IRR = 1.40. The SCRI seems robust to unmeasured confounding in the COVID-19 setting, although a strong unmeasured confounder could bias the observed effect upward. Replication of our findings for other safety signals would strengthen this conclusion.

Incretin-based therapy and the risk of diabetic foot ulcers and related events.

AIM: To investigate the effect of dipeptidyl peptidase-4 inhibitors (DPP4-Is) and glucagon-like peptide-1 receptor agonists (GLP1-RAs) on diabetic foot ulcer (DFU) and DFU-related outcomes (lower limb amputation [LLA], DFU-related hospitalization and mortality). METHODS: We performed a cohort study with data from the Clinical Practice Research Datalink Aurum database with linkage to hospital data. We included people with type 2 diabetes starting treatment with metformin. Then we propensity score matched new users of DPP4-Is and sulphonylureas (N = 98 770), and new users of GLP1-RAs and insulin (N = 25 422). Cox proportional hazards models estimated the hazard ratios (HRs) for the outcomes. RESULTS: We observed a lower risk of DFU with both DPP4-I use versus sulphonylurea use (HR 0.88, 95% confidence interval [CI]: 0.79-0.97) and GLP1-RA use versus insulin use (HR 0.44, 95% CI: 0.32-0.60) for short-term exposure (≤ 400 days) and HR 0.74 (95% CI: 0.60-0.92) for long-term exposure (>400 days). Furthermore, the risks of hospitalization and mortality were lower with both DPP4-I use and GLP1-RA use. The risk of LLA was lower with GLP1-RA use. The results remained consistent across several sensitivity analyses. CONCLUSIONS: Incretin-based therapy was associated with a lower risk of DFU and DFU-related outcomes. This suggests benefits for the use of this treatment in people at risk of DFU.

The associations of sodium-glucose cotransporter-2 inhibitors versus dipeptidyl peptidase-4 inhibitors as add-on to metformin with fracture risk in patients with type 2 diabetes mellitus.

AIM: To investigate whether sodium-glucose cotransporter-2 (SGLT2) inhibitor use as compared to dipeptidyl peptidase-4 (DPP-4) inhibitor use as add-on to metformin is associated with the risk of any fracture or major osteoporotic fractures (MOFs). METHODS: A cohort study using the Clinical Practice Research Datalink (CPRD) Aurum database was conducted. All patients aged 18 years and older with a first-ever prescription for a DPP-4 inhibitor or an SGLT2 inhibitor as add-on to metformin between January 1, 2013 and June 30, 2020 were selected. Patients starting with SGLT2 inhibitors were matched (up to 1:3) on propensity scores to patients starting with DPP-4 inhibitors. Propensity scores were calculated based on sex, age, body mass index, comorbidities, comedication and lifestyle factors. Cox proportional hazard models were used to estimate the risk of fracture with SGLT2 inhibitor use as compared to DPP-4 inhibitor use. RESULTS: A total of 13 807 SGLT2 inhibitor users (age 55.4 ± 10.6 years, 36.7% female) were included in this study, matched with 28 524 DPP-4 inhibitor users (age 55.4 ± 8.0 years, 36.4% female). The risk of any fracture with current SGLT2 inhibitor use was similar compared with current DPP-4 inhibitor use (adjusted hazard ratio [aHR] 1.09, 95% confidence interval [CI] 0.91-1.31), as was the risk of MOFs (aHR 0.89, 95% CI 0.64-1.22) and the risk of fractures at any of the individual MOF sites. Additionally, no association was found with duration of SGLT2 inhibitor use (longest duration >811 days) for any of the individual SGLT2 inhibitor agents, or after stratification by sex and age. CONCLUSION: Use of SGLT2 inhibitors was not associated with the risk of any fracture, MOFs or fracture at the individual MOF sites when compared to DPP-4 inhibitor use.

Primary nonadherence to drugs prescribed by general practitioners: A Dutch database study.

AIM: Primary nonadherence (PNA) is defined as not filling the first prescription for a drug treatment. PNA can lead not only to poor patient outcomes but also to exposure misclassification in written prescription databases. This study aims to estimate PNA in primary care in the Netherlands and to investigate associated factors. METHODS: Patients from the Nivel Primary Care Database (Nivel-PCD) who received a new prescription (>1 year not prescribed) from a general practitioner in 2012 were linked to pharmacy dispensing information of consenting pharmacies based on sex, year of birth, four-digit postal code and at least 50% matching Anatomical Therapeutic Classification codes. PNA was defined as not having a prescription dispensed within 30 days from the prescribing date. PNA was assessed overall and per drug class. The associations between PNA and several patient- and prescription-related characteristics were assessed using mixed-effects logistic regression models. RESULTS: After matching 86 361 of 396 251 subjects (21.8%) in the Nivel-PCD records to the pharmacy records, this study included 65 877 subjects who received 181 939 new drug prescriptions. Overall, PNA was 11.5%. PNA was lowest for thyroid hormones (5.5%) and highest for proton pump inhibitors (12.8%). Several factors were associated with PNA, such as having comorbidities (odds ratio [OR] 1.46, 95% confidence interval [CI] 1.37-1.56 for >3 active diagnoses, compared to no active diagnoses) or reimbursement status (OR 2.78, 95% CI 2.65-2.92 for not reimbursed drugs compared to fully reimbursed drugs). CONCLUSIONS: A total of 11.5% of newly prescribed drugs were not dispensed. This can lead to overestimation of the actual drug exposure status when using written prescription databases.

Prescribing of low-dose rivaroxaban in patients with atherosclerotic cardiovascular disease in the United Kingdom and the Netherlands.

AIMS: Low-dose rivaroxaban has been indicated for the management of atherosclerotic cardiovascular disease (ASCVD) after recent (2019-2020) updates to European guidelines. We aimed to describe prescription trends of low-dose rivaroxaban in ASCVD patients over the period 2015-2022 in two European countries, to compare the trends before and after guideline changes, and to determine the characteristics of users. METHODS: In a cross-sectional interrupted time series analysis, utilization of low-dose rivaroxaban (2.5 mg, twice daily) was measured in Clinical Practice Research Datalink Aurum (United Kingdom [UK]) and the PHARMO Database Network (the Netherlands) from 1 January 2015 to 28 February 2022 in patients with an ASCVD diagnosis. Incidence rates (IRs) and incidence rate ratios (IRRs) of new use (within 182 days) compared to the reference period, 2015-2018, were calculated. Age, sex and comorbidities of users were compared to those of nonusers. RESULTS: In the UK, from 721 271 eligible subjects the IR of new use of low-dose rivaroxaban in the period 2015-2018, before guideline changes, was 12.4 per 100 000 person-years and after guideline changes in 2020-2022 was 124.0 (IRR 10.0, 95% confidence interval [CI] 8.5, 11.8). In the Netherlands from 394 851 subjects, the IR in 2015-2018 was 2.4 per 100 000 person-years and in 2020 was 16.3 (IRR 6.7, 95% CI 4.0, 11.4). Users were younger (UK mean difference [MD] -6.1 years, Netherlands -2.4 years; P < .05) and more likely to be male (UK difference 11.5%, Netherlands 13.4%; P < .001) than nonusers. CONCLUSIONS: There was a statistically significant increase in the use of low-dose rivaroxaban for the management of ASCVD after guideline changes in the UK and the Netherlands. There were international differences, but low-dose rivaroxaban has not been put into widespread practice.

Bias in observational studies on the effectiveness of in hospital use of hydroxychloroquine in COVID-19.

PURPOSE: During the first waves of the coronavirus pandemic, evidence on potential effective treatments was urgently needed. Results from observational studies on the effectiveness of hydroxychloroquine (HCQ) were conflicting, potentially due to biases. We aimed to assess the quality of observational studies on HCQ and its relation to effect sizes. METHODS: PubMed was searched on 15 March 2021 for observational studies on the effectiveness of in-hospital use of HCQ in COVID-19 patients, published between 01/01/2020 and 01/03/2021 on. Study quality was assessed using the ROBINS-I tool. Association between study quality and study characteristics (journal ranking, publication date, and time between submission and publication) and differences between effects sizes found in observational studies compared to those found in RCTs, were assessed using Spearman's correlation. RESULTS: Eighteen of the 33 (55%) included observational studies were scored as critical risk of bias, eleven (33%) as serious risk and only four (12%) as moderate risk of bias. Biases were most often scored as critical in the domains related to selection of participants (n = 13, 39%) and bias due to confounding (n = 8, 24%). There were no significant associations found between the study quality and the characteristics nor between the study quality and the effect estimates. DISCUSSION: Overall, the quality of observational HCQ studies was heterogeneous. Synthesis of evidence of effectiveness of HCQ in COVID-19 should focus on RCTs and carefully consider the added value and quality of observational evidence.

Oral anticoagulants in patients with atrial fibrillation at low stroke risk: a multicentre observational study.

AIMS: There is currently no consensus on whether atrial fibrillation (AF) patients at low risk for stroke (one non-sex-related CHA2DS2-VASc point) should be treated with an oral anticoagulant. METHODS AND RESULTS: We conducted a multi-country cohort study in Sweden, Denmark, Norway, and Scotland. In total, 59 076 patients diagnosed with AF at low stroke risk were included. We assessed the rates of stroke or major bleeding during treatment with a non-vitamin K antagonist oral anticoagulant (NOAC), a vitamin K antagonist (VKA), or no treatment, using inverse probability of treatment weighted (IPTW) Cox regression. In untreated patients, the rate for ischaemic stroke was 0.70 per 100 person-years and the rate for a bleed was also 0.70 per 100 person-years. Comparing NOAC with no treatment, the stroke rate was lower [hazard ratio (HR) 0.72; 95% confidence interval (CI) 0.56-0.94], and the rate for intracranial haemorrhage (ICH) was not increased (HR 0.84; 95% CI 0.54-1.30). Comparing VKA with no treatment, the rate for stroke tended to be lower (HR 0.81; 95% CI 0.59-1.09), and the rate for ICH tended to be higher during VKA treatment (HR 1.37; 95% CI 0.88-2.14). Comparing NOAC with VKA treatment, the rate for stroke was similar (HR 0.92; 95% CI 0.70-1.22), but the rate for ICH was lower during NOAC treatment (HR 0.63; 95% CI 0.42-0.94). CONCLUSION: These observational data suggest that NOAC treatment may be associated with a positive net clinical benefit compared with no treatment or VKA treatment in patients at low stroke risk, a question that can be tested through a randomized controlled trial.

Impact of vomiting on P2Y12 platelet inhibition in patients with ST-elevation myocardial infarction: A prespecified subanalysis of the ON-TIME 3 trial.

Vomiting is associated with lower levels of ticagrelor concentration and higher platelet reactivity in the early hours of ST-elevation myocardial infarction. These results support reloading with a ticagrelor loading dose and/or treatment with intravenous platelet inhibitors when patients vomit.

Thiazolidinediones and Glucagon-Like Peptide-1 Receptor Agonists and the Risk of Nonalcoholic Fatty Liver Disease: A Cohort Study.

BACKGROUND AND AIMS: Thiazolidinediones (TZDs) and glucagon-like peptide-1 (GLP-1) receptor agonists are potential pharmacological treatment options for patients at risk of NAFLD. Therefore, we examined the association between the risk of NAFLD and the use of TZDs and GLP-1 receptor agonists compared with the use of sulfonylureas (SUs) and insulins. Additionally, we calculated the incidence of HCC in users of TZDs and GLP-1 receptor agonists. APPROACH AND RESULTS: We conducted a population-based cohort study using primary care data from the Clinical Practice Research Datalink database (2007-2018). All patients aged ≥18 with a prescription of an oral glucose-lowering agent or GLP-1 receptor agonist were included. The first prescription defined the start of follow-up. The primary outcome was a new diagnosis of NAFLD. Cox proportional hazards regression was used to estimate HRs and 95% CIs of the primary outcome. Incidence rates of HCC were determined per 1,000 person-years for all exposures. The study identified 207,367 adults with a prescription for a glucose-lowering agent. The risk of NAFLD was lower in patients prescribed a TZD than in those prescribed an SU (adjusted HR [aHR], 0.32; 95% CI, 0.20-0.51). No difference in risk of NAFLD was observed comparing GLP-1 receptor agonist use with insulin use (aHR, 1.22; 95% CI, 0.91-1.63). CONCLUSIONS: Results of our study endorse the use of TZDs for selected patients at risk of NAFLD but do not support previous findings regarding the beneficial effect of GLP-1 receptor agonists. The low number of events in several subgroups may affect the generalizability of the current findings.

Mapping the risk of infections in patients with multiple sclerosis: A multi-database study in the United Kingdom Clinical Practice Research Datalink GOLD and Aurum.

BACKGROUND: People with multiple sclerosis (pwMS) have an increased risk of infections; risk factors include underlying disease, physical impairment and use of some disease-modifying treatments. OBJECTIVE: To quantify changes in population-level infection rates among pwMS and compare these to the general population and people with rheumatoid arthritis (pwRA), and identify patient characteristics predictive of infections after MS diagnosis. METHODS: We conducted a multi-database study using data on 23,226 people with MS diagnosis from the UK Clinical Practice Research Datalink Aurum and GOLD (January 2000-December 2020). PwMS were matched to MS-free controls and pwRA. We calculated infection rates, and estimated incidence rate ratios (IRR) and 95% confidence intervals (CI) of predictors for infections ⩽ 5 years after MS diagnosis using Poisson regression. RESULTS: Among pwMS, overall infection rates remained stable - 1.51-fold (1.49-1.52) that in MS-free controls and 0.87-fold (0.86-0.88) that in pwRA - although urinary tract infection rate per 1000 person-years increased from 98.7 (96.1-101) (2000-2010) to 136 (134-138) (2011-2020). Recent infection before MS diagnosis was most predictive of infections (1 infection: IRR 1.92 (1.86-1.97); ⩾2 infections: IRR 3.00 (2.89-3.10)). CONCLUSION: The population-level elevated risk of infection among pwMS has remained stable despite the introduction of disease-modifying treatments.

Pre-approval and post-approval availability of evidence and clinical benefit of conditionally approved cancer drugs in Europe: A comparison with standard approved cancer drugs.

AIMS: Cancer drugs are increasingly approved through expedited regulatory pathways including the European conditional marketing authorization (CMA). Whether, when taking CMA post-approval confirmatory trials into account, the level of evidence and clinical benefit between CMA and standard approved (SMA) drugs differs remains unknown. METHODS: We identified all CMA cancer indications converted to SMA in 2006-2020 and compared these to similar SMA indications with regard to pivotal trial and CMA post-approval confirmatory trial design, outcomes and demonstrated clinical benefit (per the European Society for Medical Oncology Magnitude of Clinical Benefit Scale). We tested for differences in clinical benefit and whether substantial clinical benefit was demonstrated. To account for the clinical benefit of unconverted CMA indications, we performed sensitivity analyses. RESULTS: We included 15 SMA and 15 converted CMA cancer indications (17 remained unconverted). Approval of 11 SMA (73%) and four CMA indications (27%) was supported by a controlled trial. Improved overall survival (OS) was demonstrated for four SMA indications (27%). Improved quality of life (QoL) was demonstrated for three SMA (20%) and one CMA indication(s) (7%). Of subsequent CMA post-approval confirmatory trials, 11 were controlled (79%), one demonstrated improved OS (7%) and five improved QoL (36%). After conversion, CMA indications were associated with similar clinical benefit (P = .31) and substantial clinical benefit as SMA indications (risk ratio 1.4, 95% confidence interval 0.57-3.4). CONCLUSION: While CMA cancer indications are initially associated with less comprehensive evidence than SMA indications, levels of evidence and clinical benefit are similar after conversion from CMA to SMA.

Key Considerations in the Health Technology Assessment of Advanced Therapy Medicinal Products in Scotland, The Netherlands, and England.

OBJECTIVES: Advanced therapy medicinal products (ATMPs) are highly innovative therapies. Their costs and uncertain value claims have raised concerns among health technology assessment (HTA) bodies and payers. Little is known about how underlying considerations in HTA of ATMPs shape assessment and reimbursement recommendations. We aim to identify and assess key considerations that played a role in HTA of ATMPs underlying reimbursement recommendations. METHODS: A review of HTA reports was conducted of all authorized ATMPs in Scotland, The Netherlands, and England. Considerations were extracted and categorized into EUnetHTA Core Model domains. Per jurisdiction, considerations were aggregated and key considerations identified (defined as occurring in >1/assessment per jurisdiction). A narrative analysis was conducted comparing key considerations between jurisdictions and different reimbursement recommendations. RESULTS: We identified 15 ATMPs and 18 HTA reports. In The Netherlands and England most key considerations were identified in clinical effectiveness (EFF) and cost- and economic effectiveness (ECO) domains. In Scotland, the social aspects domain yielded most key considerations, followed by ECO and EFF. More uncertainty in evidence and assessment outcomes was accepted when orphan or end-of-life criteria were applied. A higher percentage of considerations supporting recommendations were identified for products with positive recommendations compared with restricted and negative recommendations. CONCLUSIONS: This is the first empirical review of HTA's using the EUnetHTA Core Model to identify and structure key considerations retrospectively. It provides insights in supporting and opposing considerations for reimbursement of individual products and differences between jurisdictions. Besides the EFF and ECO domain, the social, ethical, and legal domains seem to bear considerable weight in assessment of ATMPs.

Estimation of manufacturing development costs of cell-based therapies: a feasibility study.

BACKGROUND AIMS: Cell-based therapies (CBTs) provide opportunities to treat rare and high-burden diseases. Manufacturing development of these innovative products is said to be complex and costly. However, little research is available providing insight into resource use and cost drivers. Therefore, this study aimed to assess the feasibility of estimating the cost of manufacturing development of two cell-based therapy case studies using a CBT cost framework specifically designed for small-scale cell-based therapies. METHODS: A retrospective costing study was conducted in which the cost of developing an adoptive immunotherapy of Epstein-Barr virus-specific cytotoxic T lymphocytes (CTLs) and a pluripotent stem cell (PSC) master cell bank was estimated. Manufacturing development was defined as products advancing from technology readiness level 3 to 6. The study was conducted in a Scottish facility. Development steps were recreated via developer focus groups. Data were collected from facility administrative and financial records and developer interviews. RESULTS: Application of the manufacturing cost framework to retrospectively estimate the manufacturing design cost of two case studies in one Scottish facility appeared feasible. Manufacturing development cost was estimated at £1,201,016 for CTLs and £494,456 for PSCs. Most costs were accrued in the facility domain (56% and 51%), followed by personnel (20% and 32%), materials (19% and 15%) and equipment (4% and 2%). CONCLUSIONS: Based on this study, it seems feasible to retrospectively estimate resources consumed in manufacturing development of cell-based therapies. This fosters inclusion of cost in the formulation and dissemination of best practices to facilitate early and sustainable patient access and inform future cost-conscious manufacturing design decisions.

Impact of anticoagulant exposure misclassification on the bleeding risk of direct oral anticoagulants.

AIMS: Drug exposure status based on routinely collected data might be misclassified when the database contains only prescriptions from 1 type of prescriber (e.g. general practitioner and not specialist). This study aims to quantify the impact of such exposure misclassification on the risk of major bleeding and stroke/transient ischaemic attack (TIA)associated with direct oral anticoagulants (DOACs) vs. vitamin K antagonists (VKAs). METHODS: Incident anticoagulant users (>12 mo free of anticoagulation use) in the Dutch PHARMO Database Network between 2008 and 2017 were included. Drug exposure was assessed using pharmacy dispensing information. The risks of hospital admission of major bleeding for DOAC vs. VKA users was assessed with Cox regression analysis, where exposure was based on all dispensings, on general practitioner (GP)-prescribed dispensings only or on specialist-prescribed dispensings only. Hazard ratios (HRs) were estimated also for hospitalization for gastrointestinal bleeding, intracranial bleeding and stroke/TIA. RESULTS: We included 99 182 VKA-initiators and 21 795 DOAC-initiators. Use of DOAC was associated with a lower risk of major bleeding compared to VKA use; HR 0.79 (95% confidence interval 0.70-0.90), 0.78 (0.68-0.91) and 0.62 (0.50-0.76), for exposure based on complete dispensing information, only GP- and only specialist-prescribed dispensings, respectively. Similar results were found for the other bleeding outcomes. For stroke/TIA the HRs were 0.96 (0.84-1.09), 1.00 (0.84-1.18) and 0.72 (0.58-0.90), respectively. CONCLUSION: Including only GP-prescribed anticoagulant dispensings in this case did not materially impact the effect estimates compared to including all anticoagulant dispensings. Including only specialist-prescribed dispensings, however, strengthened the effect estimates.

Comparing risk of major bleeding between users of different oral anticoagulants in patients with nonvalvular atrial fibrillation.

AIMS: The introduction of direct oral anticoagulants (DOACs) has broadened the treatment arsenal for nonvalvular atrial fibrillation, but observational studies on the benefit-risk balance of DOACs compared to vitamin K antagonists (VKAs) are needed. The aim of this study was to characterize the risk of major bleeding in DOAC users using longitudinal data collected from electronic health care databases from 4 different EU-countries analysed with a common study protocol. METHODS: A cohort study was conducted among new users (≥18 years) of DOACs or VKAs with nonvalvular atrial fibrillation using data from the UK, Spain, Germany and Denmark. The incidence of major bleeding events (overall and by bleeding site) was compared between current use of DOACs and VKAs. Cox regression analysis was used to calculate hazard ratios and 95% confidence intervals (CI) and adjust for confounders. RESULTS/CONCLUSION: Overall, 251 719 patients were included across the 4 study cohorts (mean age ~75 years, % females between 41.3 and 54.3%), with overall hazard ratios of major bleeding risk for DOACs vs VKAs ranging between 0.84 (95% CI: 0.79-0.90) in Denmark and 1.13 (95% CI 1.02-1.25) in the UK. When stratifying according to the bleeding site, risk of gastrointestinal bleeding was increased by 48-67% in dabigatran users and 30-50% for rivaroxaban users compared to VKA users in all data sources except Denmark. Compared to VKAs, apixaban was not associated with an increased risk of gastrointestinal bleeding in all data sources and seemed to be associated with the lowest risk of major bleeding events compared to dabigatran and rivaroxaban.

Persistence and adherence to non-vitamin K antagonist oral anticoagulant treatment in patients with atrial fibrillation across five Western European countries.

AIMS: To assess persistence and adherence to non-vitamin K antagonist oral anticoagulant (NOAC) treatment in patients with atrial fibrillation (AF) in five Western European healthcare settings. METHODS AND RESULTS: We conducted a multi-country observational cohort study, including 559 445 AF patients initiating NOAC therapy from Stockholm (Sweden), Denmark, Scotland, Norway, and Germany between 2011 and 2018. Patients were followed from their first prescription until they switched to a vitamin K antagonist, emigrated, died, or the end of follow-up. We measured persistence and adherence over time and defined adequate adherence as medication possession rate ≥90% among persistent patients only. RESULTS: Overall, persistence declined to 82% after 1 year and to 63% after 5 years. When including restarters of NOAC treatment, 85% of the patients were treated with NOACs after 5 years. The proportion of patients with adequate adherence remained above 80% throughout follow-up. Persistence and adherence were similar between countries and was higher in patients starting treatment in later years. Both first year persistence and adherence were lower with dabigatran (persistence: 77%, adherence: 65%) compared with apixaban (86% and 75%) and rivaroxaban (83% and 75%) and were statistically lower after adjusting for patient characteristics. Adherence and persistence with dabigatran remained lower throughout follow-up. CONCLUSION: Persistence and adherence were high among NOAC users in five Western European healthcare settings and increased in later years. Dabigatran use was associated with slightly lower persistence and adherence compared with apixaban and rivaroxaban.

Drug exposure misclassification in pharmacoepidemiology: Sources and relative impact.

BACKGROUND: Drug exposure assessment based on dispensing data can be misclassified when patients do not adhere to their therapy or when information about over-the-counter drugs is not captured in the study database. Previous research has considered hypothetical sensitivity and specificity values, whereas this study aims to assess the impact of literature-based real values of exposure misclassification. METHODS: A synthetic cohort study was constructed based on the proportion of exposure theoretically captured in a database (range 0.5-1.0) and the level of adherence (0.5-1.0). Three scenarios were explored: nondifferential misclassification, differential misclassification (misclassifications dependent on an unmeasured risk factor doubling the outcome risk), and nondifferential misclassification in a comparative effectiveness study (RRA and RRB both 2.0 compared to nonuse, RRA-B 1.0). RESULTS: For the scenarios with nondifferential misclassification, 25% nonadherence or 25% uncaptured exposure changed the RR from 2.0 to 1.75, and 1.95, respectively. Applying different proportions of nonadherence or uncaptured use (20% vs. 40%) for subgroups with and without the risk factor, an RR of 0.95 was observed in the absence of a true effect (i.e., true RR = 1). In the comparative effectiveness study, no effect on RR was seen for different proportions of uncaptured exposure; however, different levels of nonadherence for the drugs (20% vs. 40%) led to an underestimation of RRA-B (0.89). DISCUSSION: All scenarios led to biased estimates, but the magnitude of the bias differed across scenarios. When testing the robustness of findings of pharmacoepidemiologic studies, we recommend using realistic values of nonadherence and uncaptured exposure based on real-world data.

A systematic review of how missing data are handled and reported in multi-database pharmacoepidemiologic studies.

PURPOSE: Pharmacoepidemiologic multi-database studies (MDBS) provide opportunities to better evaluate the safety and effectiveness of medicines. However, the issue of missing data is often exacerbated in MDBS, potentially resulting in bias and precision loss. We sought to measure how missing data are being recorded and addressed in pharmacoepidemiologic MDBS. METHODS: We conducted a systematic literature search in PubMed for pharmacoepidemiologic MDBS published between 1st January 2018 and 31st December 2019. Included studies were those that used ≥2 distinct databases to assess the same safety/effectiveness outcome associated with a drug exposure. Outcome variables extracted from the studies included strategies to execute a MDBS, reporting of missing data (type, bias evaluation) and the methods used to account for missing data. RESULTS: Two thousand seven hundred and twenty-six articles were identified, and 62 studies were included: using data from either North America (56%), Europe (31%), multiple regions (11%) or East-Asia (2%). Thirty-five (56%) articles reported missing data: 11 of these studies reported that this could have introduced bias and 19 studies reported a method to address missing data. Thirteen (68%) carried out a complete case analysis, 2 (11%) applied multiple imputation, 2 (11%) used both methods, 1 (5%) used mean imputation and 1 (5%) substituted information from a similar variable. CONCLUSIONS: Just over half of the recent pharmacoepidemiologic MDBS reported missing data and two-thirds of these studies reported how they accounted for it. We should increase our vigilance for database completeness in MDBS by reporting and addressing the missing data that could introduce bias.

Greedy caliper propensity score matching can yield variable estimates of the treatment-outcome association-A simulation study.

PURPOSE: Greedy caliper propensity score (PS) matching is dependent on randomness, which can ultimately affect causal estimates. We sought to investigate the variation introduced by this randomness. METHODS: Based on a literature search to define the simulation parameters, we simulated 36 cohorts of different sizes, treatment prevalence, outcome prevalence, treatment-outcome-association. We performed 1:1 caliper and nearest neighbor (NN) caliper PS-matching and repeated this 1000 times in the same cohort, before calculating the treatment-outcome association. RESULTS: Repeating caliper and NN caliper matching in the same cohort yielded large variations in effect estimates, in all 36 scenarios, with both types of matching. The largest variation was found in smaller cohorts, where the odds ratio (OR) ranged from 0.53 to 10.00 (IQR of ORs: 1.11-1.67). The 95% confidence interval was not consistently overlapping a neutral association after repeating the matching with both algorithms. We confirmed these findings in a noninterventional example study. CONCLUSION: Caliper PS-matching can yield highly variable estimates of the treatment-outcome association if the analysis is repeated.

Major bleeding in users of direct oral anticoagulants in atrial fibrillation: A pooled analysis of results from multiple population-based cohort studies.

OBJECTIVE: To establish the risk of major bleeding in direct oral anticoagulant (DOAC) users (overall and by class) versus vitamin K antagonist (VKA) users, using health care databases from four European countries and six provinces in Canada. METHODS: A retrospective cohort study was performed according to a similar protocol. First-users of VKAs or DOACs with a diagnosis of non-valvular atrial fibrillation (NVAF) were included. The main outcome of interest was major bleeding and secondary outcomes included gastrointestinal (GI) bleeding and intracranial haemorrhage (ICH). Incidence rates of events per 1000 person years were calculated. Hazard ratios (HRs) and 95% confidence intervals (95% CI) were estimated using a Cox proportional hazard regression model. Exposure and confounders were measured and analysed in a time-dependant way. Risk estimates were pooled using a random effect model. RESULTS: 421 523 patients were included. The risk of major bleeding for the group of DOACs compared to VKAs showed a pooled HR of 0.94 (95% CI: 0.87-1.02). Rivaroxaban showed a modestly increased risk (HR 1.11, 95% CI: 1.06-1.16). Apixaban and dabigatran showed a decreased risk of respectively HR 0.76 (95% CI: 0.69-0.84) and HR 0.85 (95% CI: 0.75-0.96). CONCLUSIONS: This study confirms that the risk of major bleeding of DOACs compared to VKAs is not increased when combining all DOACs. However, we observed a modest higher risk of major bleeding for rivaroxaban, whereas for apixaban and dabigatran lower risks of major bleeding were observed compared to VKAs.