Karolina Akinosoglou, Christos Savopoulos, Abraham Pouliakis, Charalampos Triantafyllidis, Eleftherios Markatis, Foteini Golemi, Angelos Liontos, Charikleia Vadala, Ilias C. Papanikolaou, Vasiliki Dimakopoulou, Panagiotis Xarras, Katerina Varela, Georgia Kaiafa, Athanasios Mitsianis, Anastasia Chatzistamati, Efthalia Randou, Spyridon Savvanis, Maria Pavlaki, Georgios Efraimidis, Vasileios Samaras, Dimitrios Papazoglou, Alexandra Konstantinidou, Periklis Panagopoulos, Haralampos Milionis, and on behalf of the INTERACT Study Group
(1) Background: It is well-established that coronavirus disease-2019 (COVID-19) is highly pro-inflammatory, leading to activation of the coagulation cascade. COVID-19-induced hypercoagulability is associated with adverse outcomes and mortality. Current guidelines recommend that hospitalized COVID-19 patients should receive pharmacological prophylaxis against venous thromboembolism (VTE). (2) INTERACT is a retrospective, phase IV, observational cohort study aiming to evaluate the overall clinical effectiveness and safety of a higher than conventionally used prophylactic dose of anticoagulation with tinzaparin administered for VTE prevention in non-critically ill COVID-19 patients with moderate disease severity. (3) Results: A total of 705 patients from 13 hospitals in Greece participated in the study (55% men, median age 62 years). Anticoagulation with tinzaparin was initiated immediately after admission. A full therapeutic dose was received by 36.3% of the participants (mean ± SD 166 ± 33 IU/Kgr/day) and the remaining patients (63.9%) received an intermediate dose (mean ± SD 114 ± 22 IU/Kgr/day). The median treatment duration was 13 days (Q1–Q3: 8–20 days). During the study (April 2020 to November 2021), 14 thrombotic events (2.0%) were diagnosed (i.e., three cases of pulmonary embolism (PE) and 11 cases of deep venous thrombosis, DVT). Four bleeding events were recorded (0.6%). In-hospital death occurred in 12 patients (1.7%). Thrombosis was associated with increasing age (median: 74.5 years, Q1–Q3: 62–79, for patients with thrombosis vs. 61.9 years, Q1–Q3: 49–72, p = 0.0149), increased D-dimer levels for all three evaluation time points (at admission: 2490, Q1–Q3: 1580–6480 vs. 700, Q1–Q3: 400–1475, p < 0.0001), one week ± two days after admission (3510, Q1–Q3: 1458–9500 vs. 619, Q1–Q3: 352–1054.5, p < 0.0001), as well as upon discharge (1618.5, Q1–Q3: 1010–2255 vs. 500, Q1–Q3: 294–918, p < 0.0001). Clinical and laboratory improvement was affirmed by decreasing D-dimer and CRP levels, increasing platelet numbers and oxygen saturation measurements, and a drop in the World Health Organization (WHO) progression scale. (4) Conclusions: The findings of our study are in favor of prophylactic anticoagulation with an intermediate to full therapeutic dose of tinzaparin among non-critically ill patients hospitalized with COVID-19.