The OAT Trail: The Obesity Anti-Coagulation Thromboprophylaxis Trial.

Sponsor
University College Dublin
Study ID
NCT07559643
Status
Not Yet Recruiting

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Conditions

  • Anti-Xa Activity
  • Bariatric Surgery
  • Obesity & Overweight
  • VTE (Venous Thromboembolism)

Eligibility Criteria

Sex
ALL
Age
18 Years - N/A
Healthy Volunteers
Not accepted

Interventions

  • Anti-Xa Activity Monitoring — DIAGNOSTIC_TEST
    A single venous blood sample (\~5 mL, citrated tube) drawn at 4 hours (±30 minutes) after the third consecutive LMWH dose on post-operative day 2, concurrent with routine post-operative bloods. Anti-Xa activity measured using a CE-marked in vitro diagnostic assay at the SVUH Haematology Laboratory. Results are not available in real time and do not influence clinical management. Target prophylactic range: 0.2-0.4 IU/mL per ASMBS 2021 guidance.
  • Tinzaparin (Leo) — DRUG
    Tinzaparin sodium administered subcutaneously once daily at 50 anti-Xa IU/kg total body weight for 21 days post-operatively, commencing on post-operative day 1. Used for pharmacological VTE prophylaxis following laparoscopic bariatric surgery.
  • enoxaparin — DRUG
    Enoxaparin sodium administered subcutaneously twice daily (40 mg for weight ≤150 kg; 60 mg for weight \>150 kg) for 21 days post-operatively, commencing on post-operative day 1. Used for pharmacological VTE prophylaxis following laparoscopic bariatric surgery.

Study Details

Blood clots in the legs or lungs (called venous thromboembolism or VTE) are one of the most serious complications after weight loss surgery. Most blood clots occur after patients go home from hospital, within the first 30 days after surgery. To prevent blood clots, all patients having weight loss surgery receive a daily blood-thinning injection for 21 days after their operation. Two blood-thinning injections are currently used at St Vincent's University Hospital for this purpose: enoxaparin (Clexane®) and tinzaparin (Innohep®). Both belong to a group of medicines called low molecular weight heparins (LMWHs). Patients with obesity process these medicines differently to the general population, and previous studies from our hospital have shown that fewer than 53% of patients achieve adequate blood-thinning levels with either injection when measured by a blood test called an anti-Xa level. Patients will be randomly assigned (like a coin toss) to receive either tinzaparin or enoxaparin for 21 days after their surgery. Both injections are already in routine use at this hospital. A single extra blood sample will be taken on the second day after surgery to measure the anti-Xa level, which tells us whether the injection is providing adequate protection against blood clots. This blood sample will be taken at the same time as routine post-operative blood tests so that no additional blood draws are required. The study will also look at rates of blood clots and bleeding events within 30 days of surgery, and will ask patients to complete a short questionnaire at their six-week follow-up appointment about their experience with the injection.

Key Dates

First listed
Apr 30, 2026
Start date
Aug 1, 2026
Status verified
Apr 2026
Primary completion
Aug 1, 2026
Completion
Dec 1, 2026

Study Design

Enrollment
180 participants (estimated)
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE

Arms

  • Experimental: Weight-based Tinzaparin
    Tinzaparin (Innohep®, LEO Pharma) administered subcutaneously once daily at a dose of 50 anti-Xa IU/kg total body weight, commencing on post-operative day 1 and continuing for 21 days. Administered via subcutaneous injection into the abdominal wall. Anti-Xa level measured at 4 hours (±30 minutes) after the third consecutive dose on post-operative day 2.
  • Active Comparator: Weight-stratified Enoxaparin
    Enoxaparin (Clexane®, Sanofi) administered subcutaneously twice daily, commencing on post-operative day 1 and continuing for 21 days. Dose: 40 mg twice daily for patients weighing ≤150 kg; 60 mg twice daily for patients weighing \>150 kg. Administered via subcutaneous injection into the abdominal wall. Anti-Xa level measured at 4 hours (±30 minutes) after the third consecutive dose on post-operative day 2.

Primary Outcome Measure

Proportion of participants achieving prophylactic anti-Xa levels [ Time Frame: Post-operative day 2 (4 hours after third LMWH dose) ]

Central Contacts

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