The investigators are studying whether treatment with a proton pump inhibitor called omeprazole reduces gastrointestinal bleeding in older adults taking blood thinners for a blood clot (venous thromboembolism). The purpose of this study, a pilot study or a feasibility study, is to test the study plan and determine whether enough participants will join a larger study and accept the study procedures.

Venous thromboembolism (VTE) refers to blood clots that form in the veins of the body, including the arms or legs (deep vein thrombosis [DVT]), abdomen (portal vein thrombosis), or lungs (pulmonary embolism [PE]). These blood clots are treated with medication to reduce blood clotting called anticoagulants. The main complication of anticoagulants is bleeding, the majority of which comes from the stomach or intestines (gastrointestinal tract). Anticoagulants do not cause bleeding, but they may make bleeding worse. Uncommonly, serious gastrointestinal (GI) bleeding can happen leading to hospitalization and even death. The chance of bleeding is highest in the first few months after starting anticoagulants.

Proton pump inhibitors (PPIs) are medications that lower the acid content of the stomach. The medication in this study, a type of proton pump inhibitor called omeprazole, is approved in Canada for treating stomach ulcers, heartburn, and a stomach infection called Helicobacter pylori. The use of omeprazole in this study is considered investigational. This means that Health Canada has not approved the use of omeprazole as a treatment for preventing gastrointestinal bleeding in patients taking anticoagulants. Some studies suggest that they may reduce gastrointestinal bleeding for people taking anticoagulants.

The investigators are studying whether treatment with a proton pump inhibitor called omeprazole reduces gastrointestinal bleeding in older adults taking anticoagulants for venous thromboembolism.

The investigators plan to do a large, randomized trial which is the best way to test the effect of a treatment. To do this, some of the participants in this study will get omeprazole and others will get a placebo (a substance that looks like the study omeprazole but does not have any active or medicinal ingredients). The placebo in this study is not intended to have any effect on bleeding. A placebo is used to make the results of the study more reliable.

Primary Objective To assess the feasibility of a full-scale double-blind placebo-controlled randomized trial to determine whether omeprazole reduces the risk of upper GI bleeding in older adults receiving anticoagulation for acute VTE compared to placebo.

Secondary Objectives:

1. To measure additional feasibility outcomes
2. To measure informative outcomes
3. To measure key clinical outcomes

Inclusion Criteria:

1. Male or female 65 years or older at the time of enrolment. Enrolment is limited to older adults as age is an important non-modifiable risk factor for bleeding. This will ensure the study population includes participants who may be more likely to benefit from omeprazole (compared to those with no risk factors) because all participants will have at least 1 risk factor for bleeding.
2. Newly diagnosed VTE which includes VTE at any site such as (but not limited to) DVT of upper or lower limbs, PE, cerebral vein thrombosis, portal vein thrombosis, other splanchnic vein thrombosis.
3. Planned for 3 months (90 days) or more of therapeutic anticoagulation with any anticoagulant.
4. Patient or delegate is able and willing to comply with follow-up examinations contained within the consent form.

Exclusion Criteria:

1. Therapeutic anticoagulation therapy for more than 7 days
2. Currently prescribed PPI for regular daily use (patients receiving H2 receptor antagonists will not be excluded),
3. Previous upper GI bleeding,
4. Need for dual antiplatelet therapy,
5. Contraindications to omeprazole (hypersensitivity to omeprazole, or other substituted benzimidazole PPIs, concomitant use with products that contain rilpivirine, significant drug interactions, up to the discretion of the site investigator),
6. Life expectancy is less than 3 months.

CONVERGE trials will be conducted within specific research domains under a core protocol outlining shared elements, including broad inclusion criteria, a minimum set of core outcomes, event adjudication, and data sharing to the CONVERGE shared data repository. Patients meeting domain-specific inclusion criteria can be enrolled in individual trials based on pre-defined additional characteristics. RADIANT will be the first trial conducted within the Acute VTE Treatment Domain.

Starting after study completion

Select members of the International Network of VENous Thromboembolism Clinical Research Networks (INVENT) participating in CONVERGE trials will enter into an agreement to enhance data-sharing and meta-analysis across trials. Access will be restricted by strict authentication processes and data will be maintained on secure servers.