Recurrent thrombosis despite treatment with oral NOAC can occur in the following situations:

• Non-compliance to treatment
• Using locally manufactured sub-standard brands of oral NOACs
• Obese patients with a BMI exceeding 40 kg/m² or weight of the patients exceeding 120 Kgs.
• Patients with Antiphospholipid syndrome.

In the acute emergency settings, switch to LMWH for a month or so. This should be followed by switching to and overlapping with warfarin until the INR is achieved. It is also important to keep the INR in a slightly above normal ranges i.e. 2.5 to 3.5 and in some cases 3 to 4. especially if the patient develops thrombosis despite the target INR.