Aim:
To conduct a comparative analysis of the effectiveness of basic therapy and basic therapy with the inclusion of quercetin in patients with COVID-19 with concomitant type 2 diabetes.

Material and methods:
There were examined 60 patients with COVID-19 with concomitant T2DM. Upon admission into the hospital and again after 10 days, serum levels of interleukin-6, C-reactive protein, procalcitonin, ferritin, endothelin-1 were determined, and capillaroscopy of the nail plate was performed. Patients of the group I (30) against the background of protocol therapy received 0.5 g of quercetin intravenously once a day for 10 days. Patients of the group II (30) received to basic therapy.

Results:
After the treatment in patients of the group I general weakness decreased, body temperature normalized, improved saturation indicators, the level of acute-phase parameters (interleukin-6, CRP and ferritin) significantly decreased, a positive effect of quercetin on the level of D-dimer in blood serum was noted, indices of pericapillary edema and hemosiderin deposition significantly decreased, indices diameter of the arterial part of the capillary and capillary network density significantly increased.

Conclusions:
The use of quercetin against the background of basic therapy in patients with COVID-19 and concomitant T2DM reliably reduces the level of acute-phase indices, has an important clinical significance for reducing endothelial dysfunction and for preventing thrombotic complications.