The present invention relates to an injectable sclerosant drug foam comprising: (i) denatured blood； (ii) at least one fluid； (iii) at least one sclerosant drug； (iv) a medical gas or medical gas mixture acceptable for intravenous use, (v) wherein the denatured blood is characterized by a certain level of denaturation, (vi) wherein said level of denaturation is defined by the color of the denatured blood and said color of denatured blood is comparable to or identical to blood being denatured as follows: A fresh human venous whole blood sample of 1 ml volume is heated in a cylindrical polyethylene container with 3 mm inner diameter and 3,4 mm outer diameter for about 0,5 min. to about 5 min. at a temperature of about between 75°C and 100°C and/or (vii) said level of denaturation is defined by the change of red-colored hemoglobin to brown as an indicator, wherein Fe 2+ is reduced to Fe 3+ in the hemoglobin complex to a degree of at least 80%, preferably 90% and even more preferably 95%.
