Incretin-based Drugs and the Risk of Heart Failure

The study objective is to determine whether the use of incretin-based drugs, compared with the use of oral anti-diabetic drug combinations, is associated with an increased risk of heart failure (HF) in routine clinical practice. The investigators will use a common-protocol approach to conduct retrospective cohort studies using administrative health care data from six jurisdictions (the Canadian provinces of Alberta, Manitoba, Ontario, and Saskatchewan, as well as the United States (US) MarketScan and the United Kingdom (UK) Clinical Practice Research Datalink [CPRD]). Briefly, the Canadian databases include population-level data on physician billing, diagnoses and procedures from hospital discharge abstracts, and dispensations for prescription drugs. Ontario data will be restricted to patients aged 65 years and older as prescription data are not available for younger patients. The CPRD is a clinical database that is representative of the UK population and contains the records for patients seen at over 680 general practitioner practices in the UK; these data will be linked to the Hospital Episode Statistics (HES) database, which contains in-hospital diagnosis and procedure data. US MarketScan includes individuals and their dependents covered by large U.S. employer health insurance plans, and government and public organizations.

Study population

In each jurisdiction, the investigators will assemble a base cohort that includes all patients with a first-ever prescription for a non-insulin anti-diabetic drug, including biguanides, sulfonylureas, thiazolidinediones, DPP-4 inhibitors, GLP-1 analogs, alpha-glucosidase inhibitors, meglitinides, or combinations of these drugs from the earliest availability of data at each site to the last date of availability of data. The date of prescription (for the CPRD) or dispensation (for all other sites) of the first-ever non-insulin anti-diabetic drug will define the date of base cohort entry.

From this base cohort, a study cohort will be created including all patients who initiated a new anti-diabetic drug class during the year in which incretin-based drugs entered the market in each jurisdiction or any time thereafter. These new users consist of both those who are newly-treated for diabetes, as well as those who switch to or add on a new anti-diabetic drug class not included as part of their previous treatment history. The date of study cohort entry is defined by the prescription date of the newly-prescribed drug class.

For the purpose of this study, two separate cohorts will be created based on the presence or absence of a history of HF at any time prior to and including the date of study cohort entry. Patients in each cohort will be followed from the date of study cohort entry until an event (defined below) or censoring due to death, departure from the database, loss of continuous health plan or drug plan enrolment, entry into a long-term care facility, an incident diagnosis of HIV or new prescription of HAART, or the end of the study period (June 30, 2014 or the last date of data availability at that site), whichever occurs first.

Case-control selection

The cohorts defined above will be analyzed using a nested case-control analysis, where cases are defined as a hospitalization for HF. Risk set sampling will be used to randomly select up to 20 controls for each case, matched on sex, age (± 365 days), date of study cohort entry (± 180 days), duration of treated diabetes (± 90 days), and duration of follow-up in days.

Exposure assessment

Current exposure to an anti-diabetic drug will be defined as any prescription whose duration plus a 30-day grace period overlaps with the index or event date. Current exposure will be classified hierarchically based on the following five mutually-exclusive categories: 1) incretin-based drugs; 2) insulin; 3) ≥2 oral anti-diabetic drugs used in combination therapy; 4) oral anti-diabetic drug monotherapy; and 5) no current exposure to an anti-diabetic drug. Oral anti-diabetic drugs used in combination will serve as the primary reference category as incretin-based drugs are second- to third-line therapy and thus used at a comparable point in the disease management.

Statistical analyses

All analyses will be conducted separately among patients with and without a history of HF. Conditional logistic regression will be used to estimate the odds ratios and corresponding 95% confidence intervals (CIs) of the association of hospitalization for HF, comparing current use of incretin-based drugs to oral anti-diabetic drug combinations. This is considered the primary analysis. Secondary analyses will include sub-classifying current users of incretin-based drugs by type (i.e., DPP-4 inhibitor vs GLP-1 analog) and duration of current use (≤ 365 days, 366-729 days, and ≥730 days). The potential presence of effect modification by a history of myocardial infarction (MI) will also be explored. In addition, seven sensitivity analyses will be conducted, all defined a priori, to assess the robustness of the results. Finally, all site-specific estimates will be meta-analyzed using random-effects models with inverse variance weighting, with fixed-effects analyses conducted in the sensitivity analyses. The amount of between-site heterogeneity will be estimated using the I square statistic.