The U.S. National Institute of Health (NIH) guidelines for antithrombotic therapy in patients with COVID-19 recommend prophylactic dose anticoagulation for nonpregnant adults hospitalized with COVID-19. Anticoagulant or antiplatelet therapy should not be used to prevent arterial thrombosis outside of the usual standard of care for patients without COVID-19. The guidelines do not make a recommendation for or against higher than prophylactic doses of anticoagulation due to insufficient data. Based on a meta-analysis by the American Society of Hematology, patients treated with intermediate or therapeutic doses of anticoagulation versus prophylactic doses did not confer a benefit in VTE and mortality in critically=ill patients. While there were lower odds of pulmonary embolism (odds ratio [OR] 0.09; 95% CI 0.02 to 0.57), intermediate and therapeutic doses were also associated with higher odds of major bleeding (OR 3.84; 95% CI 1.44 to 10.21). Data for therapeutic doses to prevent VTE is insufficient to form a conclusion. 
The American Society of Hematology guidance statement recommends prophylactic-intensity over intermediate or therapeutic-intensity anticoagulation in critically-ill COVID-19 patients due to lack of direct, high-quality evidence. However, they do not recommend against providers administering higher intensities of anticoagulation if they choose to. Patients should be individually assessed to determine anticoagulation intensity. [2-3]
Per Interim Guidelines from the Anticoagulation Forum published in May 2020, critically ill patients (i.e. ICU) with confirmed for highly-suspected COVID-19 are recommended to receive increased doses of VTE prophylaxis. Examples include enoxaparin 40 mg SubQ BID, enoxaparin 0.5 mg/kg SubQ BID, heparin 7500 units SubQ TID, or low-intensity heparin infusion. Doses should be adjusted based on renal function and extreme weight. This recommendation is based largely on expert opinion. 
Given the emerging evidence of clinical benefits, the Scientific and Standardization Committee (SSC) of the International Society on Thrombosis and Haemostasis (ISTH) suggests approximately 4 weeks of extended-duration VTE prophylaxis (at least 2 weeks and up to 6 weeks post-hospital discharge) either with prophylactic-dose LMWH (e.g., enoxaparin, dalteparin, tinzaparin) or a DOAC (e.g., rivaroxaban, betrixaban) for selected hospitalized COVID-19 patients who meet high VTE risk criteria (e.g., advanced age, ICU stay, cancer, history of VTE, thrombophilia, severe immobility, elevated D-diver of >2 times ULN, IMPROVE VTE score >4) with low bleed risk. 
Unlike the clinical guidance discussed above, the CHEST expert panel only recommends inpatient VTE prophylaxis due to the uncertainty around the true incidence of post-discharge VTE and potential major bleeding in COVID-19 patients with extended thromboprophylaxis. The panel observed potential net benefit of extended thromboprophylaxis only when the patient has low bleed risk, and the risk of symptomatic VTE is above 1.8% at 35-42 days post-discharge. 
The Interim Guideline from The Anticoagulation Forum recommends a full 3-month course of anticoagulation therapy for COVID-19 patients even with presumed but unconfirmed hospital-associated VTE events unless at a high risk of bleed or with a recent history of bleed. The SSC and CHEST expert panel also concur with a minimum duration of 3-month therapeutic anticoagulation therapy for VTE treatment. [5-6]
While inpatient treatment typically involves heparin, some authors suggest direct oral anticoagulants (DOACs) may be preferred for outpatients due to the ease of administration.