Comparison of the Efficacy between 81 Mg Bid of Aspirin and 162 Mg Od of Aspirin in Splenectomized Thalassemic Patients with Aspirin Resistance

Backgroud: Currently, aspirin is widely used in splenectomized thalassemic patients. Despite taking 81 mg of aspirin daily, some patients develop venous thromboembolic complications, and these patients are referred to as “aspirin-resistance”. Then, increasing dose of aspirin to 162 mg/day is one of treatment options. It is not known if which regimen of aspirin at dose of 162 mg/day (1 tab po bid VS 2 tabs po once daily) is more effective in these patients.

Methods: This is a prospective randomized cross-over study in splenectomized thalassemic patients between 2022 and 2023 at Siriraj Hospital. All splenectomized thalassemic patients aged from 18 to 60 years who have been taking aspirin of 81 mg/day were enrolled and evaluated for aspirin resistance (ASA-resist) by platelet aggregation test using arachidonic acid as agonist (PAT-AA). Patients with 81-mg aspirin resistance were randomly assigned to the following 7-day regimens in a crossover design: aspirin 81 mg twice daily (ASA1x2) or aspirin 162 mg once daily (ASA2x1), and their PAT-AA was assessed after each regimen.

Results: A total of 64 patients (41 women) with a median age of 32.5 years were mostly Hb E/beta-thalassemia (86%) whereas 53% were transfusion-dependent thalassemia (TDT). ASA-resist was found in 24 patients (37.5%). The 'ASA1x2' showed a higher prevalence of ASA-resist than 'ASA2x1' but no statistical significance (52.4% vs.35%; OR 2.0; 95%CI, 0.58-7.17; p=0.265). For 'ASA1x2' regimen, serum ferritin level of ≥1200 ng/mL was significantly associated with ASA-resist (OR 10.7; 95%CI, 1.4-82.0; p=0.030). For 'ASA2x1' regimen, ASA-resist was significantly associated with TDT (p=0.015) and serum ferritin level of ≥1200 ng/mL (OR 20.0; 95%CI, 1.7-238.6; p=0.017).

Conclusions: The “aspirin 81 mg twice daily” regimen showed a higher prevalence of aspirin resistance than “aspirin 162 mg once daily” regimen in splenectomized thalassemic patients with aspirin resistance, and an elevated serum ferritin level was significantly associated with aspirin resistance in both regimens.