Real world effectiveness of primary implantable cardioverter defibrillators implanted during hospital admissions for exacerbation of heart failure or other acute co-morbidities: cohort study of older patients with heart failure

OBJECTIVES

To examine the effectiveness of primary implantable cardioverter defibrillators (ICDs) in elderly patients receiving the device during a hospital admission for exacerbation of heart failure or other acute co-morbidities, with an emphasis on adjustment for early mortality and other factors reflecting healthy candidate bias rather than the effect of the ICD.

DESIGN

Retrospective cohort study.

SETTING

Linked data from the Centers for Medicare and Medicaid Services and American College of Cardiology-National Cardiovascular Data Registry ICD registry, nationwide heart failure registry, and Medicare claims data 2004-09.

POPULATION

23,111 patients aged ≥ 66 who were admitted to hospital for exacerbation of heart failure or other acute co-morbidities and eligible for primary ICDs.

MAIN OUTCOME MEASURES

All cause mortality and sudden cardiac death. Latency analyses with Cox regression were used to derive crude hazard ratios and hazard ratios adjusted for high dimension propensity score for outcomes after 180 days from index implantation or discharge.

RESULTS

Patients who received an ICD during a hospital admission had lower crude mortality risk than patients who did not receive an ICD (40% v 60% at three years); however, with conditioning on 180 day survival and with adjustment for high dimension propensity score, the apparent benefit with ICD was no longer evident for sudden cardiac death (adjusted hazard ratio 0.95, 95% confidence interval 0.78 to 1.17) and had a diminished impact on total mortality (0.91, 0.82 to 1.00). There were trends towards a benefit with ICD in reducing mortality or sudden cardiac death in patients who had had a myocardial infarction more than 40 days previously, left bundle branch block, or low serum B type natriuretic peptide; however, these trends did not reach significance.

CONCLUSION

After adjustment for healthy candidate bias and confounding, the benefits of primary ICD therapy seen in pivotal trials were not apparent in patients aged 66 or over who received ICDs during a hospital admission for exacerbation of heart failure or other acute co-morbidities. Future research is warranted to further identify subgroups of elderly patients who are more likely to benefit from ICDs. Recognition of those patients whose dominant risk factors are from decompensated heart failure and non-cardiac co-morbidities will allow better focus on ICDs in those patients for whom the device offers the most benefit and provides meaningful prolonging of life.

Outcomes after carotid artery stenting in Medicare beneficiaries, 2005 to 2009

IMPORTANCE

Despite increased carotid artery stenting (CAS) dissemination following the 2005 National Coverage Determination, to our knowledge, periprocedural and long-term outcomes have not been described among Medicare beneficiaries.

OBJECTIVE

To describe the incidence of outcomes during and after the periprocedural period among Medicare beneficiaries undergoing CAS.

DESIGN, SETTING, AND PARTICIPANTS

Observational study with a mean follow-up time of approximately 2 years among 22,516 fee-for-service Medicare beneficiaries at least 66 years old undergoing CAS (2005-2009) who were linked to the Centers for Medicare & Medicaid Services' CAS database. Database procedure dates were required to fall during a Medicare hospitalization for CAS.

MAIN OUTCOMES AND MEASURES

Periprocedural (30-day) and long-term risks of mortality and stroke or transient ischemic attack, as well as periprocedural myocardial infarction. Subgroups were based on sociodemographic, clinical, and center-level factors, as well as the Stenting and Angioplasty With Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) trial or Carotid Revascularization Endarterectomy vs Stenting Trial (CREST) enrollment criteria.

RESULTS

The mean patient age was 76.3 years, 60.5% were male, 93.8% were of white race, 91.2% were at high surgical risk, 47.4% were symptomatic, and 97.4% had carotid stenosis of at least 70%. Crude 30-day mortality, stroke or transient ischemic attack, and myocardial infarction risks were 1.7% (95% CI, 1.5%-1.8%), 3.3% (95% CI, 3.0%-3.5%), and 2.5% (95% CI, 2.3%-2.7%), respectively. Mortality during a mean follow-up time of 2 years was 32.0% (95% CI, 31.0%-33.0%), with rates of 37.3% (95% CI, 35.8%-38.7%) among symptomatic patients and 27.7% (95% CI, 26.4%-28.9%) among asymptomatic patients. Older age, symptomatic carotid stenosis, and nonelective hospital admission were associated with increased adjusted hazards of mortality and stroke or transient ischemic attack during and after the periprocedural period. The presence of a stroke center, government ownership, and a hospital bed capacity of 500 or more were associated with increased adjusted hazards of periprocedural mortality and stroke or transient ischemic attack. Few patients met the SAPPHIRE trial or CREST enrollment criteria primarily because physicians did not meet proficiency requirements either due to exceeding periprocedural complication trial thresholds or not meeting minimum CAS volume requirements.

CONCLUSIONS AND RELEVANCE

Competing risks may limit the benefits of CAS in certain Medicare beneficiaries, particularly among older and symptomatic patients who have higher periprocedural and long-term mortality risks. The generalizability of trials like the SAPPHIRE or CREST to the Medicare population may be limited, underscoring the need to evaluate real-world effectiveness of carotid stenosis treatments.

Surgeon case volume and 30-day mortality after carotid endarterectomy among contemporary medicare beneficiaries: before and after national coverage determination for carotid artery stenting

BACKGROUND AND PURPOSE

After the 2005 National Coverage Determination to reimburse carotid artery stenting (CAS) for Medicare beneficiaries, the number of CAS procedures increased and carotid endarterectomy (CEA) decreased. We evaluated trends in surgeons' past-year CEA case-volume and 30-day mortality after CEA, and their association before and after the National Coverage Determination.

METHODS

In a retrospective cohort study of patients undergoing CEA (2001-2008) and CAS (2005-2008) using Medicare data, we described yearly trends of CEA and CAS rates, patient characteristics, and 30-day mortality after CEA. We used logistic regression adjusting for patient- and surgeon-level factors to assess the effect of surgeon case volume on 30-day mortality after CEA.

RESULTS

We identified 454 717 CEA and 27 943 CAS patients. Patients undergoing CEA in recent years were older and had more comorbidities than earlier years. CEA rates per 10 000 beneficiaries declined from 18.1 in 2002 to 12.7 in 2008, whereas median surgeon past-year case-volume declined from 27 to 21. The CAS rates peaked at 2.3 per 10 000 beneficiaries in 2006 but declined to 1.8 in 2008, resulting in declining overall revascularization procedure rates during 2005 to 2008. Thirty day post-CEA mortality was 1.40% (95% confidence interval, 1.34-1.47) in 2001 to 2002 and 1.17% (1.10-1.24) in 2007 to 2008. Surgeon's past-year case-volume of <10 was associated with higher 30-day mortality consistently during 2001 to 2008.

CONCLUSIONS

The rate of CEA procedures decreased substantially during 2001 to 2008, as did surgeon past-year case-volume. The postprocedural mortality in Medicare beneficiaries was high compared with trial patients but somewhat improved over time. Those operated by lower past-year case-volume surgeons had increased mortality.

Accuracy of ICD-9-CM coding to identify small for gestational age newborns

PURPOSE

This study aimed to evaluate the accuracy of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis code for small for gestational age (SGA) recorded in administrative healthcare records using birthweight and gestational age information recorded in electronic medical records.

METHODS

We used billing and medical records from women aged 13-55 years who delivered at a tertiary care center in the USA between 2004 and 2011. Information on birthweight, gestational age at birth, and ICD-9-CM code for SGA, 656.5x, was abstracted from the database. Each infant's birthweight percentile for gestational age was calculated on the basis of published US references; infants below the 10th percentile were classified as SGA. The performance characteristics of SGA ICD-9-CM diagnosis code against SGA classification based on birthweight and gestational age were calculated, for all deliveries and by strata of demographic and delivery characteristics.

RESULTS

We identified 51 292 singleton live birth deliveries. The prevalence of SGA infants calculated from birthweight and gestational age at birth was higher (13%) than the prevalence based on ICD-9-CM code (2%). Sensitivity of the SGA ICD-9-CM code was 14.2%, specificity was 99.7%, positive predictive value was 86.8%, and negative predictive value was 88.4%. Stratification by demographic and delivery characteristics yielded similar results.

CONCLUSIONS

Identification of SGA infants using ICD-9-CM code, 656.5x, from administrative healthcare records has low sensitivity but high specificity; the accuracy did not differ across demographic and delivery characteristics. Thus, although this source of information would underestimate the prevalence of SGA, it could produce valid relative risk estimates.

Are risk evaluation and mitigation strategies associated with less off-label use of medications? The case of immune thrombocytopenia

Using data from a large commercial health insurer, we studied prescribing of romiplostim (Nplate) and eltrombopag (Promacta), two drugs for primary immune thrombocytopenia (ITP) for which risk evaluation and mitigation strategies (REMS) with elements to assure safe use were initially imposed and then removed. We identified 103 and 117 new users of romiplostim and eltrombopag, respectively. Use was almost exclusively for FDA-approved indications ("on-label") while the REMS with elements to assure safe use were in place. After these elements were lifted, off-label use of eltrombopag among patients with hepatitis C virus (HCV), a subsequently approved indication, increased. The ratio of incidence rate ratios of off-label/HCV to on-label initiation of eltrombopag between the two time periods was significant (13.41; P < 0.001). Our finding of an association with reduced off-label prescribing suggests that REMS with elements to assure safe use can help promote patient safety but may also prevent promising off-label drug uses.

High-dimensional propensity score algorithm in comparative effectiveness research with time-varying interventions

The high-dimensional propensity score (hdPS) algorithm was proposed for automation of confounding adjustment in problems involving large healthcare databases. It has been evaluated in comparative effectiveness research (CER) with point treatments to handle baseline confounding through matching or covariance adjustment on the hdPS. In observational studies with time-varying interventions, such hdPS approaches are often inadequate to handle time-dependent confounding and selection bias. Inverse probability weighting (IPW) estimation to fit marginal structural models can adequately handle these biases under the fundamental assumption of no unmeasured confounders. Upholding of this assumption relies on the selection of an adequate set of covariates for bias adjustment. We describe the application and performance of the hdPS algorithm to improve covariate selection in CER with time-varying interventions based on IPW estimation and explore stabilization of the resulting estimates using Super Learning. The evaluation is based on both the analysis of electronic health records data in a real-world CER study of adults with type 2 diabetes and a simulation study. This report (i) establishes the feasibility of IPW estimation with the hdPS algorithm based on large electronic health records databases, (ii) demonstrates little impact on inferences when supplementing the set of expert-selected covariates using the hdPS algorithm in a setting with extensive background knowledge, (iii) supports the application of the hdPS algorithm in discovery settings with little background knowledge or limited data availability, and (iv) motivates the application of Super Learning to stabilize effect estimates based on the hdPS algorithm.

Observational studies of the association between glucose-lowering medications and cardiovascular outcomes: addressing methodological limitations

BACKGROUND

Recent years have witnessed a growing body of observational literature on the association between glucose-lowering treatments and cardiovascular disease. However, many of the studies are based on designs or analyses that inadequately address the methodological challenges involved.

METHODS

We reviewed recent observational literature on the association between glucose-lowering medications and cardiovascular outcomes and assessed the design and analysis methods used, with a focus on their ability to address specific methodological challenges. We describe and illustrate these methodological issues and their impact on observed associations, providing examples from the reviewed literature. We suggest approaches that may be employed to manage these methodological challenges.

RESULTS

From the evaluation of 81 publications of observational investigations assessing the association between glucose-lowering treatments and cardiovascular outcomes, we identified the following methodological challenges: 1) handling of temporality in administrative databases; 2) handling of risks that vary with time and treatment duration; 3) definitions of the exposure risk window; 4) handling of exposures that change over time; and 5) handling of confounding by indication. Most of these methodological challenges may be suitably addressed through application of appropriate methods.

CONCLUSIONS/INTERPRETATION

Observational research plays an increasingly important role in the evaluation of the clinical effects of diabetes treatment. Implementation of appropriate research methods holds the promise of reducing the potential for spurious findings and the risk that the spurious findings will mislead the medical community about risks and benefits of diabetes medications.

A cross-national comparison of 17 countries' insulin glargine drug labels

PURPOSE

Type 2 diabetes mellitus has reached epidemic proportions worldwide. Many patients with type 2 diabetes mellitus will require insulin, and the evidence-based use of insulin is described in the prescription drug label. Product labels in different countries may provide inconsistent information. We evaluated the variability in drug label content for one brand of basal insulin across diverse settings.

METHODS

We examined the drug label content pertinent to effective and safe use of insulin glargine across 17 countries: Abu Dhabi (United Arab Emirates), Argentina, Brazil, Canada, China, Germany, Israel, Italy, Japan, Mexico, Russia, Saudi Arabia, South Korea, Spain, Turkey, UK, and the USA. We compared label characteristics in settings where drug labels were governed by a local regulatory authority versus countries where labels were administered by a regional body or adopted from another locale.

RESULTS

All 17 labels cautioned that providers should consider age, illness, diet, and exercise when prescribing. Only two (12%) described care of the fasting patient. Caution was urged for patients with renal or hepatic impairment in 16 (94%) labels. Four (24%) did not describe responses to missed doses, and five (29%) failed to recommend patient counseling about the risk of hypoglycemia. Labels emerging from regional or adopted regulatory bodies reported fewer patients in efficacy studies than did labels from settings with their own drug regulatory agencies (365 ± 0 patients vs. 3560 ± 2938, p = 0.04).

CONCLUSIONS

There is substantial variation in the content of drug labels for glargine, which may lead to international inconsistency in quality of care for diabetic patients.

Incidence of health insurance claims for thyroid neoplasm and pancreatic malignancy in association with exenatide: signal refinement using active safety surveillance

OBJECTIVES

As part of a regulatory postmarketing commitment, we assessed the risk of claims for thyroid and pancreatic cancer among users of exenatide using an active drug safety surveillance system.

METHODS

This active surveillance assessment used cohort methodology and commercial health insurance claims data to identify initiators of exenatide and propensity score-matched initiators of metformin or glyburide between June 2005 and September 2009, with up to 1 year of follow up through December 2009. The primary analysis estimated absolute and relative risk (RR) of inpatient or outpatient claims with diagnosis codes for thyroid neoplasm (benign or malignant) or pancreatic malignancies after exclusion of patients with a history of the same diagnosis at baseline.

RESULTS

Among the matched comparison cohorts (N ≈ 32,800 each), there were 37 claims-suggested thyroid malignancies among exenatide initiators and 26 among metformin or glyburide initiators [RR 1.4; 95% confidence interval (CI) 0.8-2.4]. This association was attenuated when limited to inpatient thyroid cancer claims (RR 0.9; CI 0.3-2.6). Exenatide use was not associated with an increased risk of benign thyroid neoplasm (RR 0.7; CI 0.3-1.7), or pancreatic cancer (RR 0.8; CI 0.5-1.6).

CONCLUSIONS

Use of exenatide was associated with a modestly higher incidence of inpatient and outpatient claims, but not inpatient claims for thyroid malignancies. Exenatide was not associated with higher risk of benign thyroid neoplasm or pancreatic cancer. Misclassification of outcomes and exposure, and residual confounding remain limitations of this analysis to be considered when interpreting the results. We have initiated a formal epidemiologic investigation to explore these relationships.

Patterns and trends in insulin intensification among patients with type 2 diabetes: a systematic review

Type 2 diabetes (T2DM) diagnoses are skyrocketing, making treatment of this disease an increasing focus of primary care visits. Guidelines recommend insulin intensification over time to achieve HbA1c targets. We conducted a systematic review regarding patterns and trends of insulin intensification and barriers to intensification. Providers across primary and specialty care settings often did not intensify insulin regimens despite patients' clinical status. Even among progressed patients, HbA1c values remained high. The paucity of available studies prevented a comprehensive understanding of patterns and trends in insulin intensification. Such information is needed to assess the quality of pharmacologic care for patients with T2DM.

Patterns of opioid utilization in pregnancy in a large cohort of commercial insurance beneficiaries in the United States

BACKGROUND

There are few data regarding the utilization of opioids during pregnancy. The objective of this study was to define the prevalence and patterns of opioid use in a large cohort of pregnant women who were commercial insurance beneficiaries.

METHODS

Data for the study were derived from a deidentified research database of women from across the United States who had both medical and prescription benefits. By using diagnostic codes, the authors defined a cohort of 534,500 women with completed pregnancies who were enrolled in a commercial insurance plan from 6 months before pregnancy through delivery.

RESULTS

Overall, 76,742 women (14.4%) were dispensed an opioid at some point during pregnancy. There were 30,566 women (5.7%) dispensed an opioid during the first trimester, 30,434 women (5.7%) during the second trimester, and 34,906 women (6.5%) during the third trimester. Of these, 11,747 women (2.2%) were dispensed opioids three or more times during pregnancy. The most commonly dispensed opioids during pregnancy were hydrocodone (6.8%), codeine (6.1%), and oxycodone (2.0%). The prevalence of exposure at anytime during pregnancy decreased slightly during the study period from 14.9% for pregnancies that delivered in 2005 to 12.9% in 2011. The prevalence of exposure varied significantly by region and was lowest in the Northeast and highest in the South.

CONCLUSIONS

This study demonstrates that opioids are very common exposures during pregnancy. Given the small and inconsistent body of literature on their safety in pregnancy, these findings suggest a need for research in this area.

Allopurinol initiation and all-cause mortality in the general population

BACKGROUND

Allopurinol is the most commonly used urate-lowering therapy, with rare but potentially fatal adverse effects. However, its impact on overall mortality remains largely unknown. In this study, we evaluated the impact of allopurinol initiation on the risk of mortality among individuals with hyperuricaemia and among those with gout in the general population.

METHODS

We conducted an incident user cohort study with propensity score matching using a UK general population database. The study population included individuals aged ≥40 years who had a record of hyperuricaemia (serum urate level >357 μmol/L for women and >416 μmol/L for men) between January 2000 and May 2010. To closely account for potential confounders of allopurinol use and risk of death, we constructed propensity score matched cohorts of allopurinol initiators and comparators (non-initiators) within 6-month cohort accrual blocks.

RESULTS

Of 5927 allopurinol initiators and 5927 matched comparators, 654 and 718, respectively, died during the follow-up (mean=2.9 years). The baseline characteristics were well balanced in the two groups, including the prevalence of gout in each group (84%). Allopurinol initiation was associated with a lower risk of all-cause mortality (matched HR 0.89 (95% CI 0.80 to 0.99)). When we limited the analysis to those with gout, the corresponding HR was 0.81 (95% CI 0.70 to 0.92).

CONCLUSIONS

In this general population study, allopurinol initiation was associated with a modestly reduced risk of death in patients with hyperuricaemia and patients with gout. The overall benefit of allopurinol on survival may outweigh the impact of rare serious adverse effects.

A cross-sectional study of the identification of prevalent asthma and chronic obstructive pulmonary disease among initiators of long-acting β-agonists in health insurance claims data

BACKGROUND

Claims data are potentially useful for identifying long-acting β-agonist (LABA) use by patients with asthma, a practice that is associated with increased mortality. We evaluated the accuracy of claims data for classifying prevalent asthma and chronic obstructive pulmonary disease (COPD) among initiators of LABAs.

METHODS

This study included adult LABA initiators during 2005-2008 in a US commercial health plan. Diagnosis codes from the 6 months before LABA initiation identified potential asthma or COPD and a physician adjudicated case status using abstracted medical records. We estimated the positive predictive value (PPV) and 95% confidence intervals (CI) of covariate patterns for identifying asthma and COPD.

RESULTS

We sought 520 medical records at random from 225,079 LABA initiators and received 370 (71%). The PPV for at least one asthma claim was 74% (CI 63-82), and decreased as age increased. Having at least one COPD claim resulted in a PPV of 82% (CI 72-89), and of over 90% among older patients, men, and recipients of inhaled anticholinergic drugs. Only 2% (CI 0.2-7.6) of patients with a claim for COPD alone were found to have both COPD and asthma, while 9% (CI 4-16) had asthma only. Twenty-one percent (CI 14-30) of patients with claims for both diagnoses had both conditions. Among patients with no asthma or COPD claims, 62% (CI 50-72) had no confirmed diagnosis and 29% (CI 19-39) had confirmed asthma.

CONCLUSIONS

Subsets of patients with asthma, COPD, and both conditions can be identified and differentiated using claims data, although categorization of the remaining patients is infeasible. Safety surveillance for off-label use of LABAs must account for this limitation.

Abstract W MP97: Trends in Volume and Mortality in CEA after Introduction of CAS in Medicare population

Background: Inverse relationship between outcome and physician volume for carotid endarterectomy (CEA) has been previously established. Following the 2005 National Coverage Determination which reimburses carotid artery stenting (CAS) for Medicare beneficiaries, the number of CAS procedures increased and the number of CEA declined. We hypothesized that the reduced number of CEA procedures resulted in lower case volumes for surgeons, adversely affecting patients' peri-procedural outcomes.

Methods: We identified inpatient CEA procedures and performing surgeons in the Medicare claims files 2001-2008. We calculated surgeon volume as the number of CEAs performed in the past 365 days and categorized volume as very low (<5), low (5-9), medium (10-29) and high (≥30). Yearly trend of: 1) rate of CEA procedures, 2) proportion of CEAs performed by categories of surgeon volume , 3) patient characteristics , and 4) 30-day mortality overall and by categories of surgeon volume, were analyzed.

Results: We identified 450,727 Medicare beneficiaries undergoing CEAs. The rate of CEA procedures per 10,000 beneficiaries declined consistently after 2002, resulting in decrease in the proportion of procedures performed by high volume surgeons (from 46% in 2002 to 33% in 2008). Patients selected for CEA became older and increased in the proportion of patients with atrial fibrillation, COPD, and chronic kidney disease, but decreased in the proportions with prior myocardial infarction and concurrent CABG. Thirty day mortality improved consistently over the years from 1.41% (95% confidence interval: 1.35-1.48) in 2001-2002 to 1.18% (1.12-1.25) in 2007-2008. This trend persisted after adjustment for patient characteristics, and in all volume categories.

Conclusion: The rate of CEA procedures decreased substantially between 2001-2008 as have performing surgeon case volumes . Dissemination of CAS has not adversely impacted the peri-procedural mortality of CEA Medicare patients.

A pooled analysis of exenatide use and risk of acute pancreatitis

OBJECTIVE

To estimate the association between exenatide BID use and acute pancreatitis across two claims-based studies.

RESEARCH DESIGN AND METHODS

We pooled two cohort studies within separate commercial health insurance databases. We included initiators of exenatide BID and all other antihyperglycemic drugs without prior pancreatitis from 2005-2008. Poisson regression models provided rate ratios (RRs) and 95% confidence intervals (CIs) of the association of exenatide BID with acute pancreatitis adjusted for quintiles of propensity scores.

MAIN OUTCOME MEASURES

Primary inpatient diagnoses of acute pancreatitis with correction for misclassification via a validation sub-study.

RESULTS

There were 49,956 initiators of exenatide BID and 692,333 initiators of other antihyperglycemic drugs. Patients in the two studies were similar on many demographic and clinical characteristics. Exenatide BID initiators had a higher prevalence of diagnoses consistent with diabetes complications (e.g. peripheral neuropathy) and cardiovascular risk factors (e.g. hypertension). In both studies, current exenatide BID use was not associated with uncorrected outcomes of acute pancreatitis (pooled RR 1.0; CI 0.8-1.3). PPV correction resulted in a slightly higher point estimate for current use (pooled RR 1.3; CI 1.0-1.7) and past use (pooled RR 1.6; 95% CI 1.2-2.1).

CONCLUSIONS

These data are consistent with little or no higher risk of acute pancreatitis associated with current exenatide BID use relative to nonuse. Although previous work identified non-causal mechanisms, an increased incidence of acute pancreatitis following cessation of treatment remains a possibility. Bias due to residual confounding or outcome misclassification may remain, and should be considered a potential explanation for these findings.

Estimation using all available covariate information versus a fixed look-back window for dichotomous covariates

PURPOSE

When using claims data, dichotomous covariates (C) are often assumed to be absent unless a claim for the condition is observed. When available historical data differs among subjects, investigators must choose between using all available historical data versus data from a fixed window to assess C. Our purpose was to compare estimation under these two approaches.

METHODS

We simulated cohorts of 20,000 subjects with dichotomous variables representing exposure (E), outcome (D), and a single time-invariant C, as well as varying availability of historical data. C was operationally defined under each paradigm and used to estimate the adjusted risk ratio of E on D via Mantel-Haenszel methods.

RESULTS

In the base case scenario, less bias and lower mean square error were observed using all available information compared with a fixed window; differences were magnified at higher modeled confounder strength. Upon introduction of an unmeasured covariate (F), the all-available approach remained less biased in most circumstances and rendered estimates that better approximated those that were adjusted for the true (modeled) value of C in all instances.

CONCLUSIONS

In most instances considered, operationally defining time-invariant dichotomous C based on all available historical data, rather than on data observed over a commonly shared fixed historical window, results in less biased estimates.

The Zelnorm epidemiologic study (ZEST): a cohort study evaluating incidence of abdominal and pelvic surgery related to tegaserod treatment

Background

Pre-marketing clinical studies of tegaserod suggested an increased risk of abdominal surgery, particularly cholecystectomy. We sought to quantify the association between tegaserod use and the occurrence of abdominal or pelvic surgery, including cholecystectomy.

Methods

This cohort study was conducted within an insured population. Tegaserod initiators and similar persons who did not initiate tegaserod were followed for up to six months for the occurrence of abdominal or pelvic surgery. Surgical procedures were identified from health insurance claims validated by review of medical records. The incidence of confirmed outcomes was compared using both as-matched and as-treated analyses.

Results

Among 2,762 tegaserod initiators, there were 94 abdominal or pelvic surgeries (36 gallbladder): among 2,762 comparators there were 134 abdominal or pelvic surgeries (37 gallbladder) (hazard ratio HR] = 0.70, 95% confidence interval [C.I.] = 0.54-0.91 overall, HR = 0.98, 95% C.I. = 0.62-1.55 for gallbladder). Current tegaserod exposure compared to nonexposure was associated with a rate ratio [RR] of 0.68 (95% C.I. = 0.48-0.95) overall, while the RR was 0.99 (95% C.I. = 0.56-1.77) for gallbladder surgery.

Conclusions

In this study, tegaserod use was not found to increase the risk of abdominal or pelvic surgery nor the specific subset of gallbladder surgery.

Rationale and design of the multinational observational study assessing insulin use: the MOSAIc study

BACKGROUND

Although consensus guidelines recommend insulin progression among patients with type 2 diabetes (T2DM) who fail to meet glycemic targets over time, many fewer patients are progressed than may benefit. We describe the rationale and design of the MOSAIc (Multinational Observational Study Assessing Insulin use) study, a multinational observational cohort study to identify patient-, physician, and health care environment-based factors associated with insulin progression for patients with T2DM in real-world practice.

METHODS/DESIGN

We will enroll 4,500 patients with T2DM taking initial insulin therapy for ≥3 months across 175 physician practice sites in 18 countries. Extensive demographic, clinical, and psychosocial data at the patient and physician level and practice site characteristics will be collected at baseline and regular intervals during a 24-month follow-up period. We will use a multivariable logistic regression model to identify predictors of insulin progression and highlight potential opportunities for health behavior intervention to improve insulin progression rates. Secondary outcomes include evaluating factors associated with glycemic control, hypoglycemia, and treatment adherence among patients who do and do not progress beyond their initial insulin therapy and exploring geographic heterogeneity in treatment.

DISCUSSION

Practice site and patient recruitment began in 2011 and baseline data will be available in late 2012. The MOSAIC study's longitudinal observational design as well as the breadth and depth of data will be used to explore and quantify predictors of insulin progression and to identify potential opportunities for health behavior intervention in order to improve T2DM treatment and clinical outcomes.