Kvasina tested positive for an experimental drug known as
Molidustat (BAY-85-3934), during two tests taken during the 2017
Flèche du Sud - a race in which he won. Molidustat represents a class of drugs that act on the same physiological pathways and enzyme cascades as those which are activated during altitude training. Oxygen deprivation has the effect of stimulating the body's production of
erythropoietin (EPO) - Molidustat imitates this. Kvasina was subsequently kicked out of the 2017
Tour of Austria. In oxygen poor environments the human body manufactures a protein called
hypoxia-inducible factor (HIF), which initiates and drives the processes which allow the body to adapt to those low-oxygen conditions. Typically this involves increasing the concentrations of naturally made EPO, mobilising iron and an increase in the rate of red blood cell production. Under normal oxygen environmental conditions, HIF is kept in check (its actions are inhibited) by an enzyme called
prolyl hydroxylase (PH). Moldustat stops PH from blocking HIF, thus, increasing both the concentrations of EPO and red blood cells in the body, imitating altitude training. ==Major results==