Table 3.

Antithrombotic prophylaxis and treatment regimens in various settings of COVID-19 infection according to international societies

Society/Document (PubMed ID number)	Antithrombotic agent and dosage	Population	Duration of treatment
COVID-19 patients WITHOUT diagnosis of VTE
International Society of Thrombosis and Haemostasis (ISTH) (PMID: 32338827)	LMWH In standard VTE prophylactic dose, in the absence of contraindications*	All COVID-19 patients who require hospitalization (including non-critically ill patients)	During the whole duration of hospital stay
STH – Subcommittee of Perioperative and Critical Thrombosis and Haemostasis of the Scientific and Standardization Committee (PMID: 32459046)	LMWH (preferred agent, once daily) OR UFH (twice or thrice daily) OR DOACs (least preferred, due to interference w/ immunosuppressant and antiviral drugs), in the absence of relevant contraindications* All in standard VTE prophylactic doses** Intermediate-dose LMWH in-hospital may be considered in severe patients	All non-ICU hospitalized COVID-19 patients	During the whole duration of hospital stay Extended duration thromboprophylaxis with LMWH or DOAC for 2–6 weeks (14 days at least, up to 30 days) post-discharge in selected patients with low risk for bleeding and key VTE risk factors could be used****
	LMWH (preferred agent, once daily) OR UFH (twice or thrice daily) All in standard VTE prophylactic doses* Intermediate-dose LMWH in-hospital can be considered in high-risk patients Full-dose heparin treatment is not recommended	All ICU hospitalized COVID-19 patients	During the whole duration of hospital stay Extended duration thromboprophylaxis with LMWH or DOAC for 2–6 weeks (14 days at least, up to 30 days) post-discharge in selected patients with low risk for bleeding and key VTE risk factors could be used****
Italian Society on Thrombosis and Haemostasis (SISET) (PMID: 32281926)	LMWH OR UFH OR fondaparinux All in standard VTE prophylactic dose, in the absence of contraindications* Intermediate-dose LMWH in-hospital (enoxaparin 4000 IU subcutaneously, twice daily) could be considered on an individual basis in patients with multiple risk factors for VTE Full-dose heparin treatment is not recommended	All hospitalized COVID-19 patients	During the whole duration of the hospital stay Maintained at home for 7–14 days post-discharge in case of pre-existing or persisting VTE risk factors
ISTH, North American Thrombosis Forum (NATF), European Society of Vascular Medicine (ESVM), International Union of Angiology (IUA), European Society of Cardiology (ESC) Working Group on the Pulmonary Circulation and Right Ventricular Function (PMID: 32311448)	LMWH, once daily, preferred agent OR UFH, twice daily Both in standard VTE prophylactic dose, in the absence of contraindications* Mechanical VTE prophylaxis in patients with contraindications in immobilized patients Prophylactic anticoagulation is the only fully recommended modality Intermediate-dose LMWH in-hospital could be an option in select patients (minority of the panel support this option) Full-dose heparin treatment is not recommended	Hospitalized patients with COVID-19 who have: respiratory failure or comorbidities such as active malignancy or heart failure, are bedridden or requiring intensive care	During the whole duration of hospital stay Extended duration thromboprophylaxis with LMWH or DOAC for up to 45 days among patients with high VTE risk and low risk of bleeding****
COVID-19 patients WITH confirmed diagnosis of VTE
International Society of Thrombosis and Haemostasis (ISTH) (PMID: 32338827)	Not discussed	N/A	N/A
ISTH – Subcommittee of Perioperative and Critical Thrombosis and Haemostasis of the Scientific and Standardization Committee (PMID: 32459046)	LMWH (inpatient setting; a change from treatment-dose DOACs or VKAs to in-hospital LMWH should be considered in critical care patients wtih relevant concomitant medications, based on renal function and thrombocyte count) DOACs (post-hospital discharge setting) Standard VTE therapeutic doses in the absence of contraindications* Prophylactic or intermediate-dose to treatment-dose regimen might be considered in patients without verified VTE but with worsening pulmonary status or ARDS	All hospitalized COVID-19 patients with established VTE	Duration of anticoagulation treatment should be at least 3 months
Italian Society on Thrombosis and Haemostasis (SISET) (PMID: 32281926)	LMWH OR UFH OR DOACs Standard VTE therapeutic doses in the absence of contraindications*	All hospitalized COVID-19 patients with established VTE	Duration of treatment in this scenario should be according to established classic guidelines for therapeutic anticoagulation of established VTE In patients requiring therapeutic doses of LMWH or DOACs, a careful monitoring of renal function with anti-factor Xa or plasma DOAC levels assays should be instituted VKAs and DOACS significantly interfere with concomitant antiviral treatment and individualized risk/benefit approach should be applied for every patient
ISTH, North American Thrombosis Forum (NATF), European Society of Vascular Medicine (ESVM), International Union of Angiology (IUA), European Society of Cardiology (ESC) Working Group on the Pulmonary Circulation and Right Ventricular Function (PMID: 32311448)	UFH, parenteral (preferred in critical patients that might undergo procedures) OR LMWH, subcutaneous (preferred in patients unlikely to undergo procedures) DOACs OR LMWH (preferred as post-discharge therapy due to reduced need for contact with healthcare workers required for INR monitoring of VKAs) All in standard VTE therapeutic doses, in the absence of contraindications* Mechanical VTE prophylaxis in patients with contraindications in immobilized patients	Hospitalized patients with COVID-19 with established VTE	Duration of treatment in this scenario should be according to established classic guidelines for therapeutic anticoagulation of established VTE

ARDS, acute respiratory distress syndrome; DOACs, direct oral anticoagulants; INR, international normalized ratio; LMWH, low molecular weight heparin; UFH-unfractionated heparin; VKA, vitamin K antagonist; VTE, venous thromboembolism

*Active bleeding, thrombocyte count < 25 × 10⁹/L, severe renal impairment (close monitoring required)

**Treatment should be modified individually according to patient’s body weight, severity of thrombocytopenia (25–50 × 10⁹ cells/L) or worsening renal function; intermittent pneumatic compression devices might be used in patients in whom anticoagulant therapy is contraindicated

***Obese patients (body mass index ≥ 30) should be considered for the 50% increase in the dose of thromboprophylaxis; multimodal prophylaxis with mechanical methods such as intermittent pneumonic compression devices should be considered

****High-risk factors defined as advanced age, stay in the ICU, cancer, a prior history of VTE, thrombophilia, severe immobility, elevated D-dimer levels (> 2 times of upper normal range), and an IMPROVE VTE score of 4 or more