Calendar time-specific propensity scores and comparative effectiveness research for stage III colon cancer chemotherapy

Proton pump inhibitors and all-cause mortality risk among cancer patients

BACKGROUND

Proton pump inhibitors (PPIs) are widely used, including among cancer patients, to manage gastroesophageal reflux and other gastric acid-related disorders. Recent evidence suggests associations between long-term PPI use and higher risks for various adverse health outcomes, including greater mortality.

AIM

To investigate the association between PPI use and all-cause mortality among cancer patients by a comprehensive analysis after adjustment for various confounders and a robust methodological approach to minimize bias.

METHODS

This retrospective cohort study used data from the TriNetX research network, with electronic health records from multiple healthcare organizations. The study employed a new-user, active comparator design, which compared newly treated PPI users with non-users and newly treated histamine2 receptor antagonists (H2RA) users among adult cancer patients. Newly prescribed PPIs (esomeprazole, lansoprazole, omeprazole, pantoprazole, or rabeprazole) users were compared to non-users or newly prescribed H2RAs (cimetidine, famotidine, nizatidine, or ranitidine) users. The primary outcome was all-cause mortality. Each patient in the main group was matched to a patient in the control group using 1:1 propensity score matching to reduce confounding effects. Multivariable Cox regression models were used to estimate hazard ratios (HRs) and 95% confidence interval (CI).

RESULTS

During the follow-up period (median 5.4 ± 1.8 years for PPI users and 6.5 ± 1.0 years for non-users), PPI users demonstrated a higher all-cause mortality rate than non-users after 1 year, 2 years, and at the end of follow up (HRs: 2.34-2.72). Compared with H2RA users, PPI users demonstrated a higher rate of all-cause mortality HR: 1.51 (95%CI: 1.41-1.69). Similar results were observed across sensitivity analyses by excluding deaths from the first 9 months and 1-year post-exposure, confirming the robustness of these findings. In a sensitivity analysis, we analyzed all-cause mortality outcomes between former PPI users and individuals who have never used PPIs, providing insights into the long-term effects of past PPI use. In addition, at 1-year follow-up, the analysis revealed a significant difference in mortality rates between former PPI users and non-users (HR: 1.84; 95%CI: 1.82-1.96).

CONCLUSION

PPI use among cancer patients was associated with a higher risk of all-cause mortality compared to non-users or H2RA users. These findings emphasize the need for cautious use of PPIs in cancer patients and suggest that alternative treatments should be considered when clinically feasible. However, further studies are needed to corroborate our findings, given the significant adverse outcomes in cancer patients.

Glucagon-Like Peptide 1 Receptor Agonists and Risk of Thyroid Cancer: An International Multisite Cohort Study

Introduction: Concerns have been raised that glucagon-like peptide 1 receptor agonists (GLP1-RAs) may increase the risk of thyroid cancer, but evidence remains conflicting. We therefore investigated if GLP1-RA use, compared with use of dipeptidyl peptidase-4 inhibitors (DPP-4is), was associated with thyroid cancer risk in patients with type 2 diabetes. Methods: This multisite cohort study with subsequent meta-analysis included six population-based databases from Canada (Ontario), Denmark, Norway, South Korea, Sweden, and Taiwan. Study populations comprised patients with type 2 diabetes between 2007 and 2023. Cox regression models estimated hazard ratios (HR) and 95% confidence intervals (CIs) for thyroid cancer among GLP1-RA users compared with DPP-4is. Models were weighted using standardized mortality ratio weights generated from time-specific propensity scores. Site-specific HRs were pooled using a fixed-effects model. Results: We identified 98,147 users of GLP1-RA and 2,488,303 users of DPP-4i, with the median follow-up among users of GLP1-RA ranging from 1.8 to 3.0 years. Overall, use of GLP1-RA relative to use of DPP-4i was not associated with an increased risk of thyroid cancer (pooled weighted HR 0.81, CI 0.59-1.12). Similarly, we observed no increased risk in thyroid cancer with increasing cumulative dose of GLP1-RA among GLP1-RA ever-users. Subgroup analysis of types of thyroid cancer was not possible. Results remained consistent across a range of supplementary analyses. Discussion: In this large multisite study, utilizing data from six population-based databases, we found no evidence that GLP1-RA use is associated with an increased risk of thyroid cancer with follow-up ranging from 1.8 to 3.0 years, providing some reassurance to patients and clinicians about the short-term safety of these drugs. Nevertheless, evidence was insufficient to rule out excess risk with long-term use, due to the short follow-up.

The Effect of Sodium Glucose Cotransporter-2 Inhibitors on Hemoglobin A1c Variability and Acute Kidney Injury: A Causal Mediation Analysis

PURPOSE

The role of lower hemoglobin A1c (HbA1c) variability in the effect of sodium glucose cotransporter-2 inhibitors (SGLT2i) on acute kidney injury (AKI) remains unclear. We compared AKI risk between SGLT2i and dipeptidyl peptidase 4 inhibitors (DPP4i) initiators. Additionally, we aimed to explore the extent to which SGLT2i's influence on AKI risk is mediated by reducing long-term HbA1c variability.

METHODS

Using 2018-2022 year data in Yinzhou Regional Health Care Database, we included adult, type 2 diabetes patients who were new users of SGLT2i or DPP4i. The effect of SGLT2i versus DPP4i on AKI, HbA1c variability, and AKI through HbA1c variability was compared using inverse probability of treatment weighted Cox proportional hazards models, median regression models, and causal mediation analysis.

RESULTS

With a median follow-up of 1.76 years, 19 717 adults (for SGLT2i, n = 6008; for DPP4i, n = 13 709) with type 2 diabetes were included. The adjusted hazard ratio for SGLT2i versus DPP4i was 0.79 (95% confidence interval [CI] 0.64-0.98) for AKI. The adjusted differences in median HbA1c variability score (HVS) and HbA1c reduction were -16.67% (95% CI: -27.71% to -5.62%) and -1.98% (95% CI: -14.34% to 10.38%), respectively. Furthermore, lower AKI risk associated with SGLT2i was moderately mediated (22.77%) through HVS. The results remained consistent across various subgroups and sensitivity analyses.

CONCLUSIONS

Compared to DPP4i, lower AKI risk associated with SGLT2i is moderately mediated through HbA1c variability. These findings enhance our understanding of the effect of SGLT2i on AKI and underscore the importance of considering HbA1c variability in diabetes treatment and management.

Risk of abnormal uterine bleeding associated with high-affinity compared with low-affinity serotonin and norepinephrine reuptake inhibitors

BACKGROUND

Concerns have been raised about the potential association between selective serotonin reuptake inhibitors (SSRIs)/serotonin-norepinephrine reuptake inhibitors (SNRIs) and the risk of abnormal uterine bleeding (AUB), which may be influenced by the affinity of SSRIs/SNRIs for serotonin transporter. Thus, we assessed whether SSRIs/SNRIs with high-affinity for serotonin transporter are associated with AUB compared to SSRIs/SNRIs with low-affinity in non-pregnant women.

METHODS

Using the UK Clinical Practice Research Datalink, we identified a cohort of women aged 15-24 years, newly prescribed a high- or low-affinity SSRI/SNRI between 1990 and 2019. Confounding was addressed using standardized morbidity ratio weighting. We used weighted Cox proportional hazards models to estimate the hazard ratio (HR) and 95 % confidence interval (CI) of AUB associated with high-affinity compared with low-affinity SSRIs/SNRIs. We assessed the risk of anemia as a secondary outcome.

RESULTS

The cohort included 156,307 users of high-affinity SSRIs/SNRIs and 102,631 users of low-affinity SSRIs/SNRIs. High-affinity SSRIs/SNRIs were not associated with an increased risk of AUB compared with low-affinity SSRIs/SNRIs (incidence rates: 46.3 versus 42.4 per 1000 person-years, respectively; HR 1.01, 95 % CI 0.93-1.09). Duration of use, age, and comorbidities did not modify the risk. However, high-affinity SSRIs/SNRIs were associated with an increased risk of anemia (HR 1.29, 95 % CI 1.04-1.61) compared with low-affinity SSRIs/SNRIs.

LIMITATIONS

Residual confounding may still be present.

CONCLUSIONS

The risk of AUB did not differ between high- and low-affinity SSRIs/SNRIs. However, the potential risk of anemia suggests the need for monitoring and further investigation of the risk of AUB with these medications.

Adaptability of High Dimensional Propensity Score Procedure in the Transition from ICD-9 to ICD-10 in the US Healthcare System

Background

High-Dimensional Propensity Score procedure (HDPS) is a data-driven approach to assist control for confounding in pharmacoepidemiologic research. The transition to the International Classification of Disease (ICD-9/10) in the US health system may pose uncertainty in applying the HDPS procedure.

Methods

We assembled a base cohort of patients in MarketScan^® Commercial Claims Database who had newly initiated celecoxib or traditional NSAIDs to compare gastrointestinal bleeding risk. We then created bootstrapped hypothetical cohorts from the base cohort with predefined patient selection patterns from the ICD eras. Three strategies for HDPS deployment were tested: 1) split the cohort by ICD era, deploy HDPS twice, and pool the relative risks (pooled RR), 2) consider codes from each ICD era as a separate data dimension and deploy HDPS in the entire cohort (data dimensions) and 3) map ICD codes from both eras to Clinical Classifications Software (CCS) concepts before deploying HDPS in the entire cohort (CCS mapping). We calculated percent bias and root-mean-squared error to compare the strategies.

Results

A similar bias reduction was observed in cohorts where patient selection pattern from each ICD era was comparable between the exposure groups. In the presence of considerable disparity in patient selection, we observed a bimodal distribution of propensity scores in the data dimensions strategy, indicating instrument-like covariates. Moreover, the CCS mapping strategy resulted in at least 30% less bias than pooled RR and data dimensions strategies (RMSE: 0.14, 0.19, 0.21, respectively) in this scenario.

Conclusion

Mapping ICD codes to a stable terminology like CCS serves as a helpful strategy to reduce residual bias when deploying HDPS in pharmacoepidemiologic studies spanning both ICD eras.

Design and analysis of outcomes following SARS-CoV-2 infection in veterans

BACKGROUND

Understanding how SARS-CoV-2 infection impacts long-term patient outcomes requires identification of comparable persons with and without infection. We report the design and implementation of a matching strategy employed by the Department of Veterans Affairs' (VA) COVID-19 Observational Research Collaboratory (CORC) to develop comparable cohorts of SARS-CoV-2 infected and uninfected persons for the purpose of inferring potential causative long-term adverse effects of SARS-CoV-2 infection in the Veteran population.

METHODS

In a retrospective cohort study, we identified VA health care system patients who were and were not infected with SARS-CoV-2 on a rolling monthly basis. We generated matched cohorts within each month utilizing a combination of exact and time-varying propensity score matching based on electronic health record (EHR)-derived covariates that can be confounders or risk factors across a range of outcomes.

RESULTS

From an initial pool of 126,689,864 person-months of observation, we generated final matched cohorts of 208,536 Veterans infected between March 2020-April 2021 and 3,014,091 uninfected Veterans. Matched cohorts were well-balanced on all 39 covariates used in matching after excluding patients for: no VA health care utilization; implausible age, weight, or height; living outside of the 50 states or Washington, D.C.; prior SARS-CoV-2 diagnosis per Medicare claims; or lack of a suitable match. Most Veterans in the matched cohort were male (88.3%), non-Hispanic (87.1%), white (67.2%), and living in urban areas (71.5%), with a mean age of 60.6, BMI of 31.3, Gagne comorbidity score of 1.4 and a mean of 2.3 CDC high-risk conditions. The most common diagnoses were hypertension (61.4%), diabetes (34.3%), major depression (32.2%), coronary heart disease (28.5%), PTSD (25.5%), anxiety (22.5%), and chronic kidney disease (22.5%).

CONCLUSION

This successful creation of matched SARS-CoV-2 infected and uninfected patient cohorts from the largest integrated health system in the United States will support cohort studies of outcomes derived from EHRs and sample selection for qualitative interviews and patient surveys. These studies will increase our understanding of the long-term outcomes of Veterans who were infected with SARS-CoV-2.

Comparative Risk of Hospitalized Bleeding of P2Y12 Inhibitors for Secondary Prophylaxis in Acute Coronary Syndrome After Percutaneous Coronary Intervention

In closely monitored randomized controlled trials (RCTs), newer P2Y12 agents (ticagrelor and prasugrel) reduced cardiovascular outcomes compared with clopidogrel following percutaneous coronary intervention (PCI) in acute coronary syndrome. However, these RCTs indicated a higher bleeding risk with these newer agents. This study evaluated the comparative safety of each P2Y12 inhibitor on hospitalizations due to major bleeding in a real-world population. This retrospective, propensity score-matched (PSM) cohort study utilized the IBM MarketScan database over 6 years (2013-2018) to identify incident users of P2Y12 inhibitors with age ≥18 years. The primary safety outcome was hospitalization due to any major bleeding event including gastrointestinal, intracranial, and other serious forms of bleeding. In pairwise comparisons using Cox-proportional hazards models, ticagrelor, prasugrel, and clopidogrel users were compared for the primary safety outcome at 30, 90, and 180 days following the first prescription of P2Y12 inhibitor after PCI. There were 21,719 (ticagrelor vs. clopidogrel), 11,513 (prasugrel vs. clopidogrel), and 11,065 (prasugrel vs. ticagrelor) PSM pairs. Overall, the risk of major bleeding was similar for all P2Y12 inhibitors. Hospitalization for major bleeding was generally lower among ticagrelor users vs. clopidogrel and higher among prasugrel users compared with clopidogrel. Importantly, a 66% higher risk of major bleeding at 90 days is suggested with prasugrel compared with clopidogrel (hazard ratio 1.66; 95% confidence interval, 1.11-2.48). This study indicated a higher short-term bleeding risk with prasugrel compared with clopidogrel, which concurs with the results of RCTs.

Comparative Effectiveness of Ticagrelor, Prasugrel, and Clopidogrel for Secondary Prophylaxis in Acute Coronary Syndrome: A Propensity Score-Matched Cohort Study

Comparative effectiveness evaluation of newer P2Y12 inhibitors (prasugrel and ticagrelor) compared with clopidogrel after acute coronary syndrome (ACS) is limited in real-world US populations. The objective of this study was to evaluate cardiovascular events based on ticagrelor, prasugrel, and clopidogrel use in a real-world patient setting. This retrospective cohort study used the IBM MarketScan database (January 1, 2013, to December 31, 2018) to create three propensity score-matched pairs: ticagrelor vs. clopidogrel (N = 21,719), prasugrel vs. clopidogrel (N = 11,513), and prasugrel vs. ticagrelor (N = 11,065). The primary outcome was a composite of myocardial ischemia, unstable angina, stroke, and heart failure hospitalization. These groups were compared in a time-to-event analysis for the primary outcome at 30, 90, and 180 days following P2Y12 inhibitors initiation after percutaneous coronary intervention. Compared with clopidogrel, ticagrelor use suggested a 10% reduction in the primary outcome at 90 days (hazard ratio (HR): 0.90, 95% confidence interval (CI): 0.82-0.99). There were no differences for all other matched pairs or follow-up combinations. In the subgroup analysis of females, the results suggested a risk reduction of 27% for prasugrel at 30 days (HR: 0.73, 95% CI: 0.53-1.00) and 17% for ticagrelor at 90 days (HR: 0.83, 95% CI: 0.70-0.98) when compared with clopidogrel. Among patients treated with bare-metal stents, the results suggested that prasugrel vs. ticagrelor was associated with a 55% and 33% reduced risk for the primary outcome at 30 days and 180 days, respectively. With limited evidence in the United States comparing these drugs, this study helps inform clinicians when choosing P2Y12 inhibitors after ACS.

Proton pump inhibitors and the risk of inflammatory bowel disease: population-based cohort study

OBJECTIVE

To determine whether the use of proton pump inhibitors (PPIs) compared with the use of histamine-2 receptor antagonists (H2RAs) is associated with an increased risk of inflammatory bowel disease (IBD).

DESIGN

Population-based cohort study designed to address the impact of protopathic bias.

SETTING

General practices contributing data to the UK Clinical Practice Research Datalink GOLD.

PARTICIPANTS

1 498 416 initiators of PPIs and 322 474 initiators of H2RAs from 1 January 1990 to 31 December 2018, with follow-up until 31 December 2019. Patients were analysed according to the timing of the IBD diagnosis after treatment initiation (early vs late).

MAIN OUTCOME MEASURES

Standardised morbidity ratio weighted Cox proportional hazards models were used to estimate marginal HRs and 95% CIs. In the early-event analysis, IBD diagnoses were assessed within the first 2 years of treatment initiation, an analysis subject to potential protopathic bias. In the late-event analysis, all exposures were lagged by 2 years to account for latency and minimise protopathic bias.

RESULTS

In the early-event analysis, the use of PPIs was associated with an increased risk of IBD within the first 2 years of treatment initiation, compared with H2RAs (HR 1.39, 95% CI 1.14 to 1.69). In contrast, the use of PPIs was not associated with an increased risk of IBD in the late-event analysis (HR 1.05, 95% CI 0.90 to 1.22). The results remained consistent in several sensitivity analyses.

CONCLUSIONS

Compared with H2RAs, PPIs were not associated with an increased risk of IBD, after accounting for protopathic bias.

Noninterventional studies in the COVID-19 era: methodological considerations for study design and analysis

The global COVID-19 pandemic has generated enormous morbidity and mortality, as well as large health system disruptions including changes in use of prescription medications, outpatient encounters, emergency department admissions, and hospitalizations. These pandemic-related disruptions are reflected in real-world data derived from electronic medical records, administrative claims, disease or medication registries, and mobile devices. We discuss how pandemic-related disruptions in healthcare utilization may impact the conduct of noninterventional studies designed to characterize the utilization and estimate the effects of medical interventions on health-related outcomes. Using hypothetical studies, we highlight consequences that the pandemic may have on study design elements including participant selection and ascertainment of exposures, outcomes, and covariates. We discuss the implications of these pandemic-related disruptions on possible threats to external validity (participant selection) and internal validity (for example, confounding, selection bias, missing data bias). These concerns may be amplified in populations disproportionately impacted by COVID-19, such as racial/ethnic minorities, rural residents, or people experiencing poverty. We propose a general framework for researchers to carefully consider during the design and analysis of noninterventional studies that use real-world data from the COVID-19 era.

Integrase Strand Transfer Inhibitors Are Associated With Incident Diabetes Mellitus in People With Human Immunodeficiency Virus

BACKGROUND

Integrase strand transfer inhibitors (INSTIs) are associated with weight gain in people with HIV (PWH). Less is known about the risk of other metabolic outcomes such as diabetes mellitus and hyperglycemia.

METHODS

IBM® MarketScan® databases for commercially and Medicaid-insured adults were used to identify PWH newly initiating antiretroviral therapy (ART). The primary outcome was a composite of new-onset diabetes mellitus/hyperglycemia in the 6 months following ART initiation and was identified using International Classification of Disease, Ninth revision, Clinical Modification (ICD-9-CM) and ICD-10-CM diagnosis and procedure codes and Current Procedural Terminology, 4th Edition (CPT-4) codes. To examine the relationship between INSTI use and the composite outcome, we estimated the risk using Cox proportional hazards models with calendar time-specific standardized mortality ratio weights.

RESULTS

Of 42 382 PWH who initiated ART between 1 July 2007 and 30 June 2018, 22 762 (54%) were treated with INSTI-based regimens. Mean age was 38 years, 74% were male, and 19% were Medicaid insured. PWH on INSTIs were 31% more likely to develop new-onset diabetes mellitus/hyperglycemia (hazard ratio [HR], 1.31; 95% confidence interval [CI], 1.15-1.48]) compared with those who initiated non-INSTI-based regimens. When examined individually, the highest risk was associated with elvitegravir (HR, 1.54; 95% CI, 1.32-1.97; P < .001) and the lowest risk with raltegravir (HR, 1.19; 95% CI, 1.03-1.37; P = .02).

CONCLUSIONS

INSTI use was associated with increased risk of new-onset diabetes mellitus/hyperglycemia in the 6 months following ART initiation.

Selective serotonin reuptake inhibitors and the risk of type 2 diabetes mellitus in youths

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) have been associated with type 2 diabetes mellitus (T2DM) in youths, possibly via 5-HT_2C, H₁ receptors and serotonin transporter (SERT). SSRIs have similar affinity for SERT but variable affinity for 5-HT_2C and H₁. This study assessed whether SSRIs with strong affinity for 5-HT_2C and H₁ (relative to SERT) were associated with T2DM risk compared with weak-affinity SSRIs.

METHODS

Using the UK Clinical Practice Research Datalink, we assembled a cohort of patients aged 5-24, newly prescribed a strong-affinity SSRI (citalopram, escitalopram, fluoxetine) or weak affinity (paroxetine, sertraline, fluvoxamine) between 1990 and 2019. We controlled for confounding using standardized mortality ratio weighting, estimated from calendar time-specific propensity scores. We used weighted Cox proportional hazards models to estimate hazard ratios (HRs) of incident T2DM with 95 % confidence intervals (CIs).

RESULTS

The cohort included 347,368 new users of strong-affinity SSRIs and 131,359 of weak-affinity SSRIs. Strong-affinity SSRIs were not associated with an increased T2DM risk compared with weak-affinity SSRIs (incidence rate 2.8 vs 2.7 per 1000 person-years; HR 1.03, 95 % CI 0.85-1.25). T2DM risk did not vary with duration of use, age or sex. However, the HR was numerically higher in youths with normal or low weight (HR 1.30, 95 % CI 0.85-1.98) and with prior antipsychotic use (HR 1.62, 95 % CI 0.83-3.18).

LIMITATIONS

Median duration of SSRI use, in line with real-world SSRI prescribing, was relatively short.

CONCLUSION

T2DM risk did not differ between strong- and weak-affinity SSRIs, providing reassurance for clinicians when choosing between SSRIs in youths.

Angiotensin-converting enzyme inhibitors and risk of age-related macular degeneration in individuals with hypertension

AIMS

Several observational studies have examined the potential protective effect of angiotensin-converting enzyme inhibitor (ACE-I) use on the risk of age-related macular degeneration (AMD) and have reported contradictory results owing to confounding and time-related biases. We aimed to assess the risk of AMD in a base cohort of patients aged 40 years and above with hypertension among new users of ACE-I compared to an active comparator cohort of new users of calcium channel blockers (CCB) using data obtained from IQVIA Medical Research Data, a primary care database in the UK.

METHODS

In this study, 53 832 and 43 106 new users of ACE-I and CCB were included between 1995 and 2019, respectively. In an on-treatment analysis, patients were followed up from the time of index drug initiation to the date of AMD diagnosis, loss to follow-up, discontinuation or switch to the comparator drug. A comprehensive range of covariates were used to estimate propensity scores to weight and match new users of ACE-I and CCB. Standardized mortality ratio weighted Cox proportional hazards model was used to estimate hazard ratios of developing AMD.

RESULTS

During a median follow-up of 2 years (interquartile range 1-5 years), the incidence rate of AMD was 2.4 (95% confidence interval 2.2-2.6) and 2.2 (2.0-2.4) per 1000 person-years among the weighted new users of ACE-I and CCB, respectively. There was no association of ACE-I use on the risk of AMD compared to CCB use in either the propensity score weighted or matched, on-treatment analysis (adjusted hazard ratio: 1.07 [95% confidence interval 0.90-1.27] and 0.87 [0.71-1.07], respectively).

CONCLUSION

We found no evidence that the use of ACE-I is associated with risk of AMD in patients with hypertension.

Potential Channeling Bias in the Evaluation of Cardiovascular Risk: The Importance of Comparator Selection in Observational Research

Background

Comparator selection is an important consideration in the design of observational research studies that evaluate potential associations between drug therapies and adverse event risks. It can affect the validity of observational study results, and potentially impact data interpretation, regulatory decision making, and patient medication access.

Objective

The aim of this study was to assess the impact of comparator selection bias using two real-world case studies evaluating an increased rate of acute myocardial infarction (AMI).

Methods

Data from the Truven Health Analytics MarketScan^® electronic medical claims database were used to conduct two retrospective observational cohort studies, utilizing a cohort new-user design, comparing AMI risk between testosterone replacement therapy (TRT) and phosphodiesterase-5 inhibitors (PDE5is) in men treated for hypogonadism, and triptans versus other prescribed acute treatments for migraine in adults. All patients were enrolled continuously in a health plan (no enrollment gap > 31 consecutive days) for ≥ 1 year before index. Baseline period was defined as 365 days prior to index. Exposure was defined by prescription and outcome of interest was defined as occurrence of AMI. Using Cox proportional hazard models, primary analysis for the TRT cohort compared AMI risk between propensity score (PS)-matched TRT-treated and untreated patients; secondary analysis evaluated risk between PS-matched TRT-treated and PDE5i-treated patients. For the triptan cohort, primary analysis compared AMI/ischemic stroke risk between PS-matched triptan-treated and opiate-treated patients; secondary analysis evaluated risk between PS-matched triptan-treated and nonsteroidal anti-inflammatory drug (NSAID)-treated patients and PS-matched non-prescription-treated migraine patients and general patients.

Results

No significant association between TRT and AMI was observed among TRT-treated (N = 198,528, mean age 52.4 ± 11.4 years) versus PDE5i-treated men (N = 198,528, mean age 52.3 ± 11.5 years) overall (adjusted hazard ratio [aHR] 1.01; 95% CI 0.95–1.07; p = 0.80). Among patients with prior cardiovascular disease (CVD), risk of AMI was significantly increased for TRT-treated versus PDE5i-treated patients (aHR 1.13; 95% CI 1.03–1.25). The triptan study included three comparisons (triptans [N = 436,642] vs prescription NSAIDs [N = 334,152], opiates [N = 55,234], and untreated migraine [N = 1,168,212]), and a positive control (untreated vs general non-migraine patients [N = 11,735,009]). Analyses of MI risk in migraine patients prescribed triptans versus NSAIDs/opiates had mixed results: the point estimate ranged from 0.33 to 0.84 depending on chosen study window.

Conclusions

Cardiovascular outcomes were not worse in hypogonadism patients with TRT versus PDE5i; however, a potential association with AMI was found in patients with prior CVD receiving TRT versus PDE5i. Findings pointed to a pseudo-protective effect of triptans versus untreated migraine patients or those potentially older and less healthy patients exposed to prescription NSAIDs or opiates. Triptan users should not be compared with those using other anti-migraine prescriptions when evaluating cardiovascular outcomes in migraine patients. Presence of high cardiovascular risks may contribute to channeling bias—healthier subjects being selected to receive treatment—highlighting the importance of choosing comparators wisely in observational studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40290-022-00433-z.

Proton pump inhibitors and risk of gastric cancer: population-based cohort study

OBJECTIVE

To determine whether new users of proton pump inhibitors (PPIs) are at an increased risk of gastric cancer compared with new users of histamine-2 receptor antagonists (H2RAs).

DESIGN

Using the UK Clinical Practice Research Datalink, we conducted a population-based cohort study using a new-user active comparator design. From 1 January 1990 to 30 April 2018, we identified 973 281 new users of PPIs and 193 306 new users of H2RAs. Cox proportional hazards models were fit to estimate HRs and 95% CIs of gastric cancer, and the number needed to harm was estimated using the Kaplan-Meier method. The models were weighted using standardised mortality ratio weights using calendar time-specific propensity scores. Secondary analyses assessed duration and dose-response associations.

RESULTS

After a median follow-up of 5.0 years, the use of PPIs was associated with a 45% increased risk of gastric cancer compared with the use of H2RAs (HR 1.45, 95% CI 1.06 to 1.98). The number needed to harm was 2121 and 1191 for five and 10 years after treatment initiation, respectively. The HRs increased with cumulative duration, cumulative omeprazole equivalents and time since treatment initiation. The results were consistent across several sensitivity analyses.

CONCLUSION

The findings of this large population-based cohort study indicate that the use of PPIs is associated with an increased risk of gastric cancer compared with the use of H2RAs, although the absolute risk remains low.

Proton pump inhibitors and risk of colorectal cancer

OBJECTIVE

To determine whether proton pump inhibitors (PPIs) are associated with an increased risk of colorectal cancer, compared with histamine-2 receptor antagonists (H2RAs).

DESIGN

The United Kingdom Clinical Practice Research Datalink was used to identify initiators of PPIs and H2RA from 1990 to 2018, with follow-up until 2019. Cox proportional hazards models were fit to estimate marginal HRs and 95% CIs of colorectal cancer. The models were weighted using standardised mortality ratio weights using calendar time-specific propensity scores. Prespecified secondary analyses assessed associations with cumulative duration, cumulative dose and time since treatment initiation. The number needed to harm was calculated at five and 10 years of follow-up.

RESULTS

The cohort included 1 293 749 and 292 387 initiators of PPIs and H2RAs, respectively, followed for a median duration of 4.9 years. While the use of PPIs was not associated with an overall increased risk of colorectal cancer (HR: 1.02, 95% CI 0.92 to 1.14), HRs increased with cumulative duration of PPI use (<2 years, HR: 0.93, 95% CI 0.83 to 1.04; 2-4 years, HR: 1.45, 95% CI 1.28 to 1.60; ≥4 years, HR: 1.60, 95% CI 1.42 to 1.80). Similar patterns were observed with cumulative dose and time since treatment initiation. The number needed to harm was 5343 and 792 for five and 10 years of follow-up, respectively.

CONCLUSION

While any use of PPIs was not associated with an increased risk of colorectal cancer compared with H2RAs, prolonged use may be associated with a modest increased risk of this malignancy.

Renin-Angiotensin-Aldosterone System Inhibitors and Risk of Acute Pancreatitis: A Population-Based Cohort Study

INTRODUCTION

There are conflicting reports on the effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) on acute pancreatitis incidence.

OBJECTIVE

The aim was to determine whether use of ACE inhibitors and ARBs is associated with the incidence of acute pancreatitis, compared with use of dihydropyridine calcium channel blockers (dCCBs).

METHODS

We assembled two population-based, new-user, active comparator cohorts using the United Kingdom Clinical Practice Research Datalink linked to the Hospital Episode Statistics repository and Office for National Statistics from 1998 to 2018, with follow-up until 2019. The first cohort included 304,083 ACE inhibitor initiators and 194,431 dCCB initiators. The second cohort included 29,160 ARB initiators and 203,610 dCCB initiators. Cox proportional hazards models were fit to estimate hazard ratios (HRs) with 95% confidence intervals (CIs) of acute pancreatitis, comparing ACE inhibitors and ARBs, separately, with dCCBs. Models were weighted using standardized mortality ratio weights generated from calendar time-specific propensity scores.

RESULTS

ACE inhibitors were associated with an increased risk of acute pancreatitis, compared with dCCBs (64.3 vs 45.2 per 100,000 person-years, respectively; HR 1.45, 95% CI 1.15-1.83). The number needed to harm after 2 and 5 years of use was 2438 and 1019, respectively. In contrast, ARBs were not associated with an increased risk of acute pancreatitis, compared with dCCBs (40.1 vs 47.6 per 100,000 person-years, respectively; HR 0.88, 95% CI 0.60-1.31).

CONCLUSIONS

ACE inhibitors were associated with a modest increased risk of acute pancreatitis compared with dCCBs. This association should be balanced with the known clinical benefits of ACE inhibitors in hypertension management. In contrast, no association was observed with ARBs.

Effectiveness of angiotensin-neprilysin inhibitor treatment versus renin-angiotensin system blockade in older adults with heart failure in clinical care

OBJECTIVE

To evaluate the effectiveness of angiotensin receptor-neprilysin inhibitor (ARNI) versus renin-angiotensin system (RAS) blockade alone in older adults with heart failure with reduced ejection fraction (HFrEF).

METHODS

We conducted a cohort study using US Medicare fee-for-service claims data (2014-2017). Patients with HFrEF ≥65 years were identified in two cohorts: (1) initiators of ARNI or RAS blockade alone (ACE inhibitor, ACEI; or angiotensin receptor blocker, ARB) and (2) switchers from an ACEI to either ARNI or ARB. HR with 95% CI from Cox proportional hazard regression and 1-year restricted mean survival time (RMST) difference with 95% CI were calculated for a composite outcome of time to first worsening heart failure event or all-cause mortality after adjustment for 71 pre-exposure characteristics through propensity score fine-stratification weighting. All analyses of initiator and switcher cohorts were conducted separately and then combined using fixed effects.

RESULTS

51 208 patients with a mean age of 76 years were included, with 16 193 in the ARNI group. Adjusted HRs comparing ARNI with RAS blockade alone were 0.92 (95% CI 0.84 to 1.00) among initiators and 0.79 (95% CI 0.74 to 0.85) among switchers, with a combined estimate of 0.84 (95% CI 0.80 to 0.89). Adjusted 1-year RMST difference (95% CI) was 4 days in the initiator cohort (-1 to 9) and 12 days (8 to 17) in the switcher cohort, resulting in a pooled estimate of 9 days (6 to 12) favouring ARNI.

CONCLUSION

ARNI treatment was associated with lower risk of a composite effectiveness endpoint compared with RAS blockade alone in older adults with HFrEF.

Brief Report: Integrase Strand Transfer Inhibitors Are Associated With Lower Risk of Incident Cardiovascular Disease in People Living With HIV

BACKGROUND

Several antiretroviral therapy (ART) classes have been associated with increased myocardial infarction (MI) risk. Cardiovascular disease in people living with HIV (PLWH) on integrase strand transfer inhibitors (INSTI) has not been examined. Here we aim to examine this.

SETTING

Retrospective cohort design study.

METHODS

We used the IBMMarketScan databases for U.S. commercially insured and Medicaid covered adults to identify PLWH newly initiated on ART between January 1, 2008 and December 30, 2015. Major adverse cardiac event (MACE), a composite of acute MI, ischemic stroke, coronary artery bypass grafting, and percutaneous coronary intervention was the primary outcome. We used calendar time-specific probability-weighted Cox proportional hazards models to estimate hazard ratios and 95% confidence intervals for the association between INSTI use and MACE. We used propensity score weighting methods to account for potential confounding.

RESULTS

Twenty thousand two hundred forty-two new ART initiators were identified. 5069 (25%) PLWH initiated INSTI-based regimens. 203 MACE events occurred; acute MI 16 (0.32%) vs 66 (0.43%), stroke 24 (0.47%) vs 54 (0.36), coronary artery bypass grafting 2 (0.04%) vs 9 (0.06%), percutaneous coronary intervention 7 (0.14%) vs 25 (0.16%) of INSTI users vs non-users. INSTI-based ART was associated with significantly lower risk of MACE events (hazard ratios 0.79; 95% confidence intervals: 0.64 to 0.96) compared with non-INSTI-based regimens.

CONCLUSION

In this cohort, INSTI-based regimens were associated with a 21% decreased risk of incident cardiovascular disease. These finding require validation in other cohorts and with longer follow-up.

Effectiveness of adjuvant FOLFOX vs 5FU/LV in adults over age 65 with stage II and III colon cancer using a novel hybrid approach

PURPOSE

Estimates of cancer therapy effects can differ in clinical trials and clinical practice, partly due to underrepresentation of certain patient subgroups in trials. We utilize a hybrid approach, combining clinical trial and real-world data, to estimate the comparative effectiveness of two adjuvant chemotherapy regimens for colon cancer.

METHODS

We identified patients aged 66 and older enrolled in the Multicenter International Study of Oxaliplatin/5FU-LV in the Adjuvant Treatment of Colon Cancer. Similar patients were identified in the Surveillance, Epidemiology, and End Results (SEER)-Medicare database, initiating adjuvant chemotherapy with either 5-fluorouracil (5FU) alone or in combination with oxaliplatin (FOLFOX). We used logistic regression to estimate the likelihood of trial enrollment as a function of age, sex, and substage. Using inverse odds of sampling weights (IOSW), we compared 5-year mortality in patients randomized to FOLFOX vs 5FU using weighted Cox proportional hazards regression, the Nelson-Aalen estimator for cumulative hazards, and bootstrapping for 95% confidence intervals (CIs).

RESULTS

There were 690 trial participants and 3834 SEER-Medicare patients. The SEER-Medicare population was older and had a higher proportion of stage IIIB and IIIC patients than the trial. After controlling for differences between populations, the IOSW 5-year HR was 1.21 (0.89, 1.65), slightly farther from the null than the trial estimate (HR = 1.14, 95%CI: 0.87, 1.49).

CONCLUSIONS

This study supports mounting evidence of little to no incremental reduction in 5-year mortality for FOLFOX vs 5FU in older adults with stage II-III colon cancer, emphasizing the importance of combining clinical trial and real-world data to support such conclusions.

Incidence of venous thromboembolism following initiation of non-steroidal anti-inflammatory drugs in U.S. women

OBJECTIVE

To evaluate the risk of venous thromboembolism (VTE, i.e. deep vein thrombosis or pulmonary embolism, or both) following new use of NSAIDs in a long-term cohort of U.S. women.

METHODS

We investigated initiation of coxibs and traditional NSAIDs (excluding aspirin) and incident VTE in 39 876 women enrolled in the Women's Health Study from 1993-95 and followed with yearly questionnaires until 2012. We defined initiation as the first reported use of NSAIDs for ≥4 days per month. Incident VTE was confirmed by an end point committee. We estimated hazard ratios (HRs) and risk differences (RDs, expressed as percentages) comparing NSAID initiation with non-initiation and acetaminophen initiation (active comparator) via standardization using a propensity score that incorporated age, BMI, calendar time, and relevant medical, behavioural, and socioeconomic variables updated over time.

RESULTS

The HR (95% CI) for risk of VTE in the as treated analyses comparing initiation with non-initiation, was 1.5 (1.2, 1.8) for any NSAID, 1.3 (1.1, 1.7) for traditional NSAIDs, and 2.0 (1.3, 3.1) for coxibs, with 2-year RDs 0.11, 0.08 and 0.32, respectively. When comparing the risk of VTE after initiation of any NSAID with that after acetaminophen initiation, the HRs were 0.9 (0.6, 1.5), 0.9 (0.5, 1.5) and 1.4 (0.6, 3.4), with 2-year RDs 0.03, -0.01, and 0.13, respectively.

CONCLUSION

New use of NSAIDs was associated with increased VTE risk compared with non-use, but the association was null or diminished when compared with acetaminophen initiation. Elevated VTE risks associated with NSAID use in observational studies may in part reflect different baseline risks among individuals who need analgesics and may overstate the risk patients incur compared with pharmacologic alternatives.

Matching with time-dependent treatments: A review and look forward

Observational studies of treatment effects attempt to mimic a randomized experiment by balancing the covariate distribution in treated and control groups, thus removing biases related to measured confounders. Methods such as weighting, matching, and stratification, with or without a propensity score, are common in cross‐sectional data. When treatments are initiated over longitudinal follow‐up, a target pragmatic trial can be emulated using appropriate matching methods. The ideal experiment of interest is simple; patients would be enrolled sequentially, randomized to one or more treatments and followed subsequently. This tutorial defines a class of longitudinal matching methods that emulate this experiment and provides a review of existing variations, with guidance regarding study design, execution, and analysis. These principles are illustrated in application to the study of statins on cardiovascular outcomes in the Framingham Offspring cohort. We identify avenues for future research and highlight the relevance of this methodology to high‐quality comparative effectiveness studies in the era of big data.

Evaluating utilization patterns of oral anticoagulants in routine care

Essentials Unlike warfarin, treatment with DOACs do not require regular plasma level monitoring. We compared persistence of patients treated with DOACs compared to warfarin. Persistence at 12 months was higher for all DOACs compared to warfarin. Persistence to anticoagulant therapy was generally poor in commercially insured patients.

BACKGROUND

Direct oral anticoagulants (DOACs) were developed as an alternative to vitamin K antagonists for a variety of indications. Unlike warfarin, DOACs do not require regular plasma level monitoring.

OBJECTIVE

We investigated whether this simplification in management affects persistence on DOACs vs warfarin.

METHODS

Within two US commercial health insurance databases (MarketScan and Clinformatics™ DataMart), we compared baseline characteristics and evaluated rates of nonpersistence (≥30-day treatment gap or switching) among patients with nonvalvular atrial fibrillation who initiated an oral anticoagulant between October 2010 and September 2015.

RESULTS

In the larger of the two data sources (MarketScan), we identified 166 690 anticoagulant initiators during the study period. After propensity score (PS) matching, 24 141 dabigatran initiators, 26 066 rivaroxaban, and 12 578 apixaban initiators were included along with the 1:1 matched warfarin initiators. The proportion of patients who were nonpersistent after 12 months was lower for DOAC users (dabigatran 66%, rivaroxaban 60%, apixaban 53%) compared with warfarin users (72%). The same relative ranking was observed in direct comparisons among the DOACs after PS-matching. Findings in Clinformatics DataMart were similar.

CONCLUSION

Results from this long-term surveillance program showed that patients who initiated DOACs were more likely to be persistent to therapy compared with those who initiated warfarin. Persistence to anticoagulant therapy was generally poor in commercially insured patients.

Testosterone Therapy and Risk of Acute Myocardial Infarction in Hypogonadal Men: An Administrative Health Care Claims Study

BACKGROUND

There are some ongoing debates on the potential link between testosterone therapy (TT) and risk of acute myocardial infarction (MI).

AIM

To investigate the association between acute MI and TT use compared with non-use in men having documented hypogonadism (diagnostic International Classification of Diseases, Ninth Revision codes 257.2, 257.8, 257.9, 758.7) in patient claims records.

METHODS

This retrospective cohort study used a real-world US-based administrative health care claims database (MarketScan 2004-2013; Truven Health Analytics, Ann Arbor, MI, USA) to compare MI rates between TT-treated men and a cohort of untreated hypogonadal men matched by a calendar time-specific propensity score. Subgroup analyses were performed by route of administration, age, and prior cardiovascular disease (CVD).

OUTCOMES

Incidence rates of MI (per 1,000 person-years) and hazard ratio.

RESULTS

After 1:1 calendar time-specific propensity score matching, 207,176 TT-treated men and 207,176 untreated hypogonadal men were included in the analysis (mean age = 51.8 years). Incidence rates of MI were 4.20 (95% CI = 3.87-4.52) in the TT-treated cohort and 4.67 (95% CI = 4.43-4.90) in the untreated hypogonadal cohort. Cox regression model showed no significant association between TT use and MI when comparing TT-treated with untreated hypogonadal men overall (hazard ratio = 0.99, 95% CI = 0.89-1.09), by age, or by prior CVD. A significant association was observed when comparing a subgroup of injectable (short- and long-acting combined) TT users with untreated hypogonadal men (hazard ratio = 1.55, 95% CI = 1.24-1.93).

CLINICAL IMPLICATION

In this study, there was no association between TT (overall) and risk of acute MI.

STRENGTHS AND LIMITATIONS

Strengths included the use of a comprehensive real-world database, sophisticated matching based on calendar blocks of 6 months to decrease potential bias in this observational study, carefully chosen index dates for the untreated cohort to avoid immortal time bias, and implemented sensitivity analysis to further investigate the findings (stratification by administration route, age, and prior CVD). Key limitations included no information about adherence, hypogonadism condition based solely on diagnosis (no information on clinical symptoms or testosterone levels), lack of information on disease severity, inability to capture diagnoses, medical procedures, and medicine dispensing if corresponding billing codes were not generated and findings could contain biases or fail to generalize well to other populations.

CONCLUSION

This large, retrospective, real-world observational study showed no significant association between TT use and acute MI when comparing TT-treated with untreated hypogonadal men overall, by age, or by prior CVD; the suggested association between injectable TT and acute MI deserves further investigation. Li H, Mitchell L, Zhang X, et al. Testosterone Therapy and Risk of Acute Myocardial Infarction in Hypogonadal Men: An Administrative Health Care Claims Study. J Sex Med 2017;14:1307-1317.

Optimal Timing of Physician Visits after Hospital Discharge to Reduce Readmission

OBJECTIVE

To identify the optimal timing of in-person physician visit after hospital discharge to yield the largest reduction in readmission among elderly or chronically ill patients.

DATA SOURCES/STUDY SETTING/EXTRACTION METHODS

We extracted insurance billing data on 620,656 admissions for any cause from 2002 to 2009 in Quebec, Canada.

STUDY DESIGN

We used flexible survival models to estimate inverse probability weights for the precise timing (days) of in-person physician visit after discharge and weighted competing risk outcome models.

PRINCIPAL FINDINGS

Readmission reduction associated with in-person physician visits (compared to none) was seen early after discharge, with 67.8 fewer readmissions per 1,000 discharges if physician visit occurred within 7 days (95 percent CI: 66.7-69.0), and 110.0 fewer readmissions within 21 days (95 percent CI: 108.2-111.7). The period of largest contribution to readmission reduction was seen in the first 10 days, while physician visits occurring later than 21 days after discharge did not further contribute to reducing hospital readmissions. Larger risk reductions were observed among patients in the highest morbidity level and for in-person follow-up with a primary care physician rather than a medical specialist.

CONCLUSIONS

When provided promptly, postdischarge in-person physician visit can prevent many readmissions. The benefits appear optimal when such visit occurs within the first 10 days, or at least within the first 21 days of discharge.

Data-Adaptive Estimation for Double-Robust Methods in Population-Based Cancer Epidemiology: Risk Differences for Lung Cancer Mortality by Emergency Presentation

In this paper, we propose a structural framework for population-based cancer epidemiology and evaluate the performance of double-robust estimators for a binary exposure in cancer mortality. We conduct numerical analyses to study the bias and efficiency of these estimators. Furthermore, we compare 2 different model selection strategies based on 1) Akaike's Information Criterion and the Bayesian Information Criterion and 2) machine learning algorithms, and we illustrate double-robust estimators' performance in a real-world setting. In simulations with correctly specified models and near-positivity violations, all but the naive estimators had relatively good performance. However, the augmented inverse-probability-of-treatment weighting estimator showed the largest relative bias. Under dual model misspecification and near-positivity violations, all double-robust estimators were biased. Nevertheless, the targeted maximum likelihood estimator showed the best bias-variance trade-off, more precise estimates, and appropriate 95% confidence interval coverage, supporting the use of the data-adaptive model selection strategies based on machine learning algorithms. We applied these methods to estimate adjusted 1-year mortality risk differences in 183,426 lung cancer patients diagnosed after admittance to an emergency department versus persons with a nonemergency cancer diagnosis in England (2006-2013). The adjusted mortality risk (for patients diagnosed with lung cancer after admittance to an emergency department) was 16% higher in men and 18% higher in women, suggesting the importance of interventions targeting early detection of lung cancer signs and symptoms.

Assessment of channeling bias among initiators of glucose-lowering drugs: A UK cohort study

Background

Channeling bias may occur when a newly marketed drug and an established drug, despite similar indications, are prescribed to patients with different prognostic characteristics (ie, confounding).

Aim

To investigate channeling bias and its impact on relative effectiveness of glucagon-like peptide-1 (GLP-1) analogs versus basal insulin and dipeptidyl peptidase-4 inhibitors (DPP-4i) versus sulfonylurea.

Methods

In the UK Clinical Practice Research Datalink, patients with type 2 diabetes initiating treatment between 2006 and 2015 were included. Analyses were stratified by years since first prescription of GLP-1 and DPP-4i, respectively. The characteristics of GLP-1 versus insulin and DPP-4i versus sulfonylurea initiators were compared over time. After propensity score matching, the relative effectiveness regarding 6-month changes in glycated hemoglobin (HbA_1c) and body weight was estimated.

Results

In total, 8,398 GLP-1, 14,807 insulin, 24,481 DPP-4i, and 33,505 sulfonylurea initiators were identified. No major channeling was observed. Considerable overlap in distributions of characteristics allowed for propensity score-matched analyses. Relative effectiveness was similar across time. The overall relative effect of GLP-1 versus insulin showed no difference for HbA_1c and relative increase in body weight (3.57 kg [95% confidence interval {CI}: 3.21, 3.92]) for insulin. The overall relative effect of DPP-4i versus sulfonylurea showed relative decrease in HbA_1c (−0.34% [95% CI: −0.38, −0.30]) and increase in body weight (1.58 kg [95% CI: 1.38, 1.78]) for sulfonylurea.

Conclusion

No major channeling was identified in the investigated glucose-lowering drugs. Relative effectiveness could be estimated already in the first year after launch and was consistent in the years thereafter.

Safety and effectiveness of dabigatran and warfarin in routine care of patients with atrial fibrillation

The RE-LY study demonstrated the safety and efficacy of dabigatran relative to warfarin for stroke prevention in non-valvular atrial fibrillation. It is important to further evaluate safety and effectiveness of drugs in routine care. This study used a sequential cohort design with propensity score matching to compare dabigatran with warfarin among patients in two commercial health insurance databases. New users of these anticoagulants were followed from initiation until discontinuation, the end of the study, or the occurrence of a study outcome (primary study outcomes were stroke and major bleeding). Proportional hazards regression was conducted separately within each data source and results were pooled. Among 19,189 matched dabigatran and warfarin initiators (mean age: 68 years, 36 % female), as-treated follow-up (average of 5 months for dabigatran, 4 months for warfarin) identified 62 and 69 strokes, respectively (pooled HR = 0.77; 95 % CI = 0.54 to 1.09), and 354 and 395 major haemorrhages, respectively (HR = 0.75; 0.65 to 0.87). No meaningful heterogeneity was identified across subgroups, but numeric trends suggest more pronounced stroke prevention by dabigatran relative to warfarin among patients age 75+ (HR = 0.57; 0.33 to 0.97) or with < 6 months of use (HR = 0.51; 0.19 to 1.42). Major bleeds were reduced more by dabigatran among patients aged < 55 (HR = 0.51; 0.30 to 0.87) and with CHADS2 < 2 (HR = 0.58; 0.44 to 0.77). In conclusion, in routine care of patients with non-valvular atrial fibrillation, dabigatran treatment resulted in improved health outcomes compared with warfarin.

Comparative Effectiveness of Oxaliplatin Versus 5-flourouricil in Older Adults: An Instrumental Variable Analysis

BACKGROUND

Oxaliplatin was rapidly adopted for treatment of stage III colon cancer after FDA approval in November 2004, thus providing an opportunity to use calendar time as an instrumental variable in nonexperimental comparative effectiveness research. Assuming instrument validity, instrumental variable analyses account for unmeasured confounding and are particularly valuable in sub-populations of unresolved effectiveness, such as older individuals.

METHODS

We examined stage III colon cancer patients ages 65+ years initiating chemotherapy between 2003 and 2008 using US population-based cancer registry data linked with Medicare claims (N = 3,660). Risk differences for all-cause mortality were derived from Kaplan-Meier survival curves. We examined instrumental variable strength and compared risk differences with propensity score estimates.

RESULTS

Calendar time greatly affected oxaliplatin receipt. The calendar time instrument compared patients treated from January 2003 through September 2004 (N = 1,449) with those treated from March 2005 through May 2007 (N = 1,432), resulting in 54% compliance. The 1-, 2-, and 3-year local average treatment effect of the risk differences per 100 patients in the "compliers" (95% confidence intervals) were -4.6 (-8.2, -0.44), -6.3 (-12, -0.16), and -9.2 (-15, -2.5), respectively. Corresponding propensity score-matched results were -1.9 (-4.0, 0.2), -3.4 (-6.2, -0.05), and -4.3 (-7.5, -0.96).

CONCLUSIONS

Instrumental variable and propensity score analyses both indicate better survival among patients treated with oxaliplatin. As these results are based on different populations and assumptions, the instrumental variable analysis adds to evidence of oxaliplatin's effectiveness in older adults, who bear the greatest burden of colon cancer yet were underrepresented in clinical trials. In nonexperimental comparative effectiveness research of rapidly emerging therapies, the potential to use calendar time as an instrumental variable is worth consideration.

Matching on the disease risk score in comparative effectiveness research of new treatments

PURPOSE

We use simulations and an empirical example to evaluate the performance of disease risk score (DRS) matching compared with propensity score (PS) matching when controlling large numbers of covariates in settings involving newly introduced treatments.

METHODS

We simulated a dichotomous treatment, a dichotomous outcome, and 100 baseline covariates that included both continuous and dichotomous random variables. For the empirical example, we evaluated the comparative effectiveness of dabigatran versus warfarin in preventing combined ischemic stroke and all-cause mortality. We matched treatment groups on a historically estimated DRS and again on the PS. We controlled for a high-dimensional set of covariates using 20% and 1% samples of Medicare claims data from October 2010 through December 2012.

RESULTS

In simulations, matching on the DRS versus the PS generally yielded matches for more treated individuals and improved precision of the effect estimate. For the empirical example, PS and DRS matching in the 20% sample resulted in similar hazard ratios (0.88 and 0.87) and standard errors (0.04 for both methods). In the 1% sample, PS matching resulted in matches for only 92.0% of the treated population and a hazard ratio and standard error of 0.89 and 0.19, respectively, while DRS matching resulted in matches for 98.5% and a hazard ratio and standard error of 0.85 and 0.16, respectively.

CONCLUSIONS

When PS distributions are separated, DRS matching can improve the precision of effect estimates and allow researchers to evaluate the treatment effect in a larger proportion of the treated population. However, accurately modeling the DRS can be challenging compared with the PS.

Provider-based research networks may improve early access to innovative colon cancer treatment for African Americans treated in the community

BACKGROUND

African American (AA) patients with colon cancer (CC) experience worse outcomes than whites partly due to differential treatment. The National Cancer Institute's Community Clinical Oncology Program (CCOP), a provider-based research network, adopts and diffuses innovative CC treatments quickly. The authors hypothesized that CCOP participation would lessen racial differences in the receipt of oxaliplatin, an innovative treatment for CC, among patients with stage III CC in the community.

METHODS

Using Surveillance, Epidemiology, and End Results (SEER)-Medicare data, the authors performed a population-based retrospective cohort study of AA and white individuals aged ≥66 years who were diagnosed with AJCC stage III CC from 2003 through 2005. Generalized estimating equations were used to calculate the odds of receiving an oxaliplatin-containing regimen. Predicted probabilities of oxaliplatin receipt for race-CCOP combinations were calculated. The absolute difference in oxaliplatin receipt between races was estimated using the interaction contrast ratio.

RESULTS

Of 2971 included individuals, 36% received oxaliplatin, 29.5% were CCOP-affiliated, and 7.6% were AA. On multivariate analysis, early diffusion of oxaliplatin was not found to be associated with race or CCOP participation. The probability of receiving oxaliplatin for AAs participating in a CCOP (0.46) was nearly double that of AAs who were not participating in a CCOP (0.25; P <.05). For white individuals, the probabilities of receiving oxaliplatin did not differ by CCOP participation. For oxaliplatin receipt, the joint effects assessment suggested a greater benefit of CCOP participation among AAs (interaction contrast ratio, 1.7).

CONCLUSIONS

Among older patients with stage III CC, there is a differential impact of race on oxaliplatin receipt depending on CCOP participation. AAs treated by CCOPs were more likely to receive oxaliplatin than AAs treated elsewhere. Provider-based research networks may facilitate early access to innovative treatment for AAs with stage III CC.

The effectiveness of the cardiovascular disease prevention programme 'KardioPro' initiated by a German sickness fund: a time-to-event analysis of routine data

Background

Cardiovascular disease is the leading cause of morbidity and mortality in the developed world. To reduce this burden of disease, a German sickness fund (‘Siemens-Betriebskrankenkasse’, SBK) initiated the prevention programme ‘KardioPro’ including primary (risk factor reduction) and secondary (screening) prevention and guideline-based treatment. The aim of this study was to assess the effectiveness of ‘KardioPro’ as it is implemented in the real world.

Methods

The study is based on sickness fund routine data. The control group was selected from non-participants via propensity score matching. Study analysis was based on time-to-event analysis via Cox proportional hazards regression with the endpoint ‘all-cause mortality, acute myocardial infarction (MI) and ischemic stroke (1)’, ‘all-cause mortality (2)’ and ‘non-fatal acute MI and ischemic stroke (3)’.

Results

A total of 26,202 insurants were included, 13,101 participants and 13,101 control subjects. ‘KardioPro’ enrolment was associated with risk reductions of 23.5% (95% confidence interval (CI) 13.0–32.7%) (1), 41.7% (95% CI 30.2–51.2%) (2) and 3.5% (hazard ratio 0.965, 95% CI 0.811–1.148) (3). This corresponds to an absolute risk reduction of 0.29% (1), 0.31% (2) and 0.03% (3) per year.

Conclusion

The prevention programme initiated by a German statutory sickness fund appears to be effective with regard to all-cause mortality. The non-significant reduction in non-fatal events might result from a shift from fatal to non-fatal events.

Model Misspecification When Excluding Instrumental Variables From PS Models in Settings Where Instruments Modify the Effects of Covariates on Treatment

Theory and simulations show that variables affecting the outcome only through exposure, known as instrumental variables (IVs), should be excluded from propensity score (PS) models. In pharmacoepidemiologic studies based on automated healthcare databases, researchers will sometimes use a single PS model to control for confounding when evaluating the effect of a treatment on multiple outcomes. Because these "full" models are not constructed with a specific outcome in mind, they will usually contain a large number of IVs for any individual study or outcome. If researchers subsequently decide to evaluate a subset of the outcomes in more detail, they can construct reduced "outcome-specific" models that exclude IVs for the particular study. Accurate estimates of PSs that do not condition on IVs, however, can be compromised when simply excluding instruments from the full PS model. This misspecification may have a negligible impact on effect estimates in many settings, but is likely to be more pronounced for situations where instruments modify the effects of covariates on treatment (instrument-confounder interactions). In studies evaluating drugs during early dissemination, the effects of covariates on treatment are likely modified over calendar time and IV-confounder interaction effects on treatment are likely to exist. In these settings, refitting more flexible PS models after excluding IVs and IV-confounder interactions can work well. The authors propose an alternative method based on the concept of marginalization that can be used to remove the negative effects of controlling for IVs and IV-confounder interactions without having to refit the full PS model. This method fits the full PS model, including IVs and IV-confounder interactions, but marginalizes over values of the instruments. Fitting more flexible PS models after excluding IVs or using the full model to marginalize over IVs can prevent model misspecification along with the negative effects of balancing instruments in certain settings.

Instrumental variable additive hazards models

Instrumental variable (IV) methods are popular in non-experimental studies to estimate the causal effects of medical interventions. These approaches allow for the consistent estimation of treatment effects even if important confounding factors are unobserved. Despite the increasing use of these methods, there have been few extensions of IV methods to censored data problems. In this article, we discuss challenges in applying IV techniques to the proportional hazards model and demonstrate the utility of the additive hazards formulation for IV analyses with censored data. Assuming linear structural equation models for the hazard function, we develop a closed-form, two-stage estimator for the causal effect in the additive hazard model. The methods permit both continuous and discrete exposures, and enable the estimation of causal relative survival measures. The asymptotic properties of the estimators are derived and the resulting inferences are shown to perform well in simulation studies and in an application to a data set on the effectiveness of a novel chemotherapeutic agent for colon cancer.

Comparative Analysis of Calendar Time-Specific and Conventional Propensity Score Analysis for Thiazolidinedione Use in Diabetes

OBJECTIVES

To evaluate whether there are differences in propensity score (PS) and treatment effects estimated using conventional and calendar time-specific PS (CTS-PS) approaches.

METHODS

A retrospective database analysis at a university-affiliated hospital in Thailand was used. Diabetic patients receiving glucose-lowering medications from July 2008 to June 2011 were included. Patients were categorized into those exposed and not exposed to thiazolidinediones (TZDs). PSs were estimated by using conventional PS and CTS-PS. In the CTS-PS, PS was separately estimated for three specific calendar time periods. Patients were matched 1:1 using caliper matching. The outcomes were cardiovascular and all-cause hospitalizations. The TZD and non-TZD groups were compared with Cox proportional hazard models.

RESULTS

A total of 2165 patients were included. The average conventional PS was 0.198 (95% confidence interval [CI] 0.195-0.202), while the average PS in the CTS-PS approach was 0.212 (0.206-0.218), 0.180 (0.173-0.188), and 0.205 (0.197-0.213) for July 2008 to June 2009, July 2009 to June 2010, and July 2010 to June 2011, respectively. The average difference in PS was 0.012 (P < 0.001), -0.009 (P ≤ 0.002), and 0.000 (P = 0.950) in the three calendar time periods. The adjusted hazard ratios of the conventional PS-matched cohort were 0.97 (95% CI 0.39-2.45) and 0.97 (95% CI 0.78-1.20) for CVD-related and all-cause hospitalizations, while the adjusted hazard ratios of the CTS-PS-matched cohort were 1.11 (95% CI 0.43-2.88) and 1.12 (95% CI 0.91-1.39), respectively.

CONCLUSION

CTS-PS is different from PS estimated by using the conventional approach. CTS-PS should be considered when a pattern of medication use has changed over the study period.

Pre-study feasibility and identifying sensitivity analyses for protocol pre-specification in comparative effectiveness research

The use of healthcare databases for comparative effectiveness research (CER) is increasing exponentially despite its challenges. Researchers must understand their data source and whether outcomes, exposures and confounding factors are captured sufficiently to address the research question. They must also assess whether bias and confounding can be adequately minimized. Many study design characteristics may impact on the results; however, minimal if any sensitivity analyses are typically conducted, and those performed are post hoc. We propose pre-study steps for CER feasibility assessment and to identify sensitivity analyses that might be most important to pre-specify to help ensure that CER produces valid interpretable results.

Sequential cohort design applying propensity score matching to analyze the comparative effectiveness of atorvastatin and simvastatin in preventing cardiovascular events

Background

Sequential cohort design (SCD) applying matching for propensity scores (PS) in accrual periods has been proposed to mitigate bias caused by channeling when calendar time is a proxy for strong confounders. We studied the channeling of patients according to atorvastatin and simvastatin initiation in Finland, starting from the market introduction of atorvastatin in 1998, and explored the SCD PS approach to analyzing the comparative effectiveness of atorvastatin versus simvastatin in the prevention of cardiovascular events (CVE).

Methods

Initiators of atorvastatin or simvastatin use in the 45–75-year age range in 1998–2006 were characterized by their propensity of receiving atorvastatin over simvastatin, as estimated for 17 six-month periods. Atorvastatin (10 mg) and simvastatin (20 mg) initiators were matched 1∶1 on the PS, as estimated for the whole cohort and within each period. Cox regression models were fitted conventionally, and also for the PS matched cohort and the periodically PS matched cohort, to estimate the hazard ratios (HR) for CVEs.

Findings

Atorvastatin (10 mg) was associated with a 11%–12% lower incidence of CVE in comparison with simvastatin (20 mg). The HR estimates were the same for a conventional Cox model (0.88, 95% confidence interval 0.85–0.91), for the analysis in which the PS was used to match across all periods and the Cox model was adjusted for strong confounders (0.89, 0.85–0.92), and for the analysis in which PS matching was applied within sequential periods (0.88, 0.84–0.92). The HR from a traditional PS matched analysis was 0.80 (0.77–0.83).

Conclusions

The SCD PS approach produced effect estimates similar to those obtained in matching for PS within the whole cohort and adjusting the outcome model for strong confounders, but at the cost of efficiency. A traditional PS matched analysis without further adjustment in the outcome model produced estimates further away from unity.

Changing patterns of use of osteoporosis medications in the years after launch: implications for comparative effectiveness research

PURPOSE

Newly marketed medications may be used selectively in patients with more severe disease. Changes in patterns of use following a drug's introduction to the market can greatly influence results from non-experimental comparative effectiveness research. We sought to explore this issue by characterizing trends in oral and injectable prescription drug claims for the prevention and treatment of osteoporosis.

METHODS

We examined a post-menopausal population of women age 55 years and older in the Truven Health Analytics MarketScan® Databases. We used propensity score (PS) methods to describe how predictors of new users of oral and injectable osteoporosis medications change over time.

RESULTS

We found that injectable osteoporosis medications tended to be used more selectively in the higher risk patients shortly after launch. Over time, they appeared to be used increasingly in lower risk patients.

CONCLUSION

If disease severity is incompletely captured in the data, comparative effectiveness of novel osteoporosis medications may be difficult to accurately estimate, particularly when medications are new to market.

Calendar time-specific propensity score analysis for observational data: a case study estimating the effectiveness of inhaled long-acting beta-agonist on asthma exacerbations

PURPOSE

Propensity scores (PS) are frequently used in observational studies. PS are usually estimated over the entire study period without consideration of the effect of changing patterns of the included variables over time. This study sought to compare PS estimated using the entire study period (conventional PS) and PS estimated for specific periods (calendar time-specific PS (CTS-PS)), and to determine whether there are differences in estimated treatment effects using these approaches.

METHODS

We conducted a claims data analysis. Asthmatic patients who received an asthma controller during 1997-2008 were included. Exposed patients were those who received an inhaled long-acting beta-2 agonist. Conventional PS used the entire period to estimate a PS for individuals. CTS-PS approach divided the study period into 1-year periods and estimated PS separately for each period. Each individual had two PS. Both PS approaches were used to estimate adjusted hazard ratio (HR) for asthma exacerbations using Cox proportional hazard models.

RESULTS

A total of 288,518 patients with an average age of 11.9 ± 5.8 years were included. The difference between conventional PS and CTS-PS in each period ranged from -0.213 to 0.098. The adjusted HR of conventional PS-matched cohort was 1.20 (95%CI: 1.18-1.22), whereas the estimate for the CTS-PS-matched cohort was 1.24 (95%CI: 1.23-1.37).

CONCLUSION

Focusing on a specific year, there was a difference between conventional PS estimated versus CTS-PS for that year. However, there was minimal effect of CTS-PS on the observed treatment effects compared with conventional PS approach.

Validity of the Danish National Registry of Patients for chemotherapy reporting among colorectal cancer patients is high

BACKGROUND

The Danish National Registry of Patients (DNRP) is a potentially valuable resource for monitoring national trends in the use of chemotherapy and evaluating the benefits and harms of alternative treatments among colorectal cancer (CRC) patients in Denmark. However, the validity of chemotherapy reporting in the DNRP is unknown. In this study, we evaluated the validity of the DNRP for identifying the receipt of chemotherapy and specific treatments, and the timing and number of treatments among CRC patients, using medical records and pharmacy data as the reference standard.

METHODS

We selected a random sample of CRC patients with lymph node involvement who were diagnosed at Aarhus University Hospital (n = 25) or Aalborg University Hospital (n = 25) from 2009 to 2010. Administration dates, specific treatments, and number of treatment courses were abstracted for the 180 days post diagnosis from the DNRP, medical records, and pharmacy production databases. The prevalence of chemotherapy, timing of first administration, and number of courses were described. DNRP data were compared with the reference standard for each hospital, and the kappa, sensitivity, specificity, positive and negative predictive values, and 95% confidence intervals were calculated for the receipt of any chemotherapy and specific treatments.

RESULTS

The prevalence of chemotherapy was 72% and 68% among CRC patients treated in Aarhus and Aalborg, respectively, with >90% of patients without distant metastasis receiving treatment within 90 days from diagnosis. Patients received on average 4.6 and 4.7 treatment courses in Aarhus and Aalborg, respectively. Kappa, sensitivity, and specificity of chemotherapy reporting in the DNRP was high (≥0.88), but the sensitivity of individual chemotherapies varied by hospital.

CONCLUSION

The validity of chemotherapy reporting in the DNRP was high, although some variation by hospital exists. The DNRP represents a population-based nationwide resource that can be used to provide timely and accurate evaluations of chemotherapy use among CRC patients in Denmark.

Propensity score estimation to address calendar time-specific channeling in comparative effectiveness research of second generation antipsychotics

Background

Channeling occurs when a medication and its potential comparators are selectively prescribed based on differences in underlying patient characteristics. Drug safety advisories can provide new information regarding the relative safety or effectiveness of a drug product which might increase selective prescribing. In particular, when reported adverse effects vary among drugs within a therapeutic class, clinicians may channel patients toward or away from a drug based on the patient's underlying risk for an adverse outcome. If channeling is not identified and appropriately managed it might lead to confounding in observational comparative effectiveness studies.

Objective

To demonstrate channeling among new users of second generation antipsychotics following a Food and Drug Administration safety advisory and to evaluate the impact of channeling on cardiovascular risk estimates over time.

Data Source

Florida Medicaid data from 2001–2006.

Study Design

Retrospective cohort of adults initiating second generation antipsychotics. We used propensity scores to match olanzapine initiators with other second generation antipsychotic initiators. To evaluate channeling away from olanzapine following an FDA safety advisory, we estimated calendar time-specific propensity scores. We compare the performance of these calendar time-specific propensity scores with conventionally-estimated propensity scores on estimates of cardiovascular risk.

Principal Findings

Increased channeling away from olanzapine was evident for some, but not all, cardiovascular risk factors and corresponded with the timing of the FDA advisory. Covariate balance was optimized within period and across all periods when using the calendar time-specific propensity score. Hazard ratio estimates for cardiovascular outcomes did not differ across models (Conventional PS: 0.97, 95%CI: 0.81–3.18 versus calendar time-specific PS: 0.93, 95%CI: 0.77–3.04).

Conclusions

Changes in channeling over time was evident for several covariates but had limited impact on cardiovascular risk estimates, possibly due to unmeasured confounding. Although calendar time-specific propensity scores appear to improve covariate balance, the impact on comparative effectiveness results is limited in this setting.