Horse welfare during competition is dependent on that relevant withdrawal times for pharmaceuticals guarantee only irrelevant drug concentrations to be present in the body in order to decrease the injury rate. Therefore, it is essential to find a relevant biomarker for therapeutic effect of glucocorticoids in order to achieve more relevant withdrawal times. A first-rate biomarker candidate is annexin-1, a protein regulated by endogenous glucocorticoids and of great importance for the anti- inflammatory and analgesic effect. The aim is to relate the plasma concentrations of the glucocorticoid dexamethasone to annexin-1 plasma concentrations and consequently establish the therapeutic plasma concentration, which is essential when deciding relevant withdrawal time and optimal dose. Furthermore a biomarker for the therapeutic effect of dexamethasone will in the long term be an efficient tool to establish withdrawal times for all glucocorticoids to assure horse welfare.