Ans. a. Hydroxyurea The only drug approved by US FDA for the treatment of sickle cell anemia is hydroxyurea.Hydroxyurea in Sickle Cell Anemia* The only drug approved by US FDA for the treatment of sickle cell anemia is hydroxyurea.* Hydroxyurea increases total and fetal hemoglobin in children with sickle cell disease.* The increase in fetal hemoglobin retards sickling of RBCs.* Hydroxyurea also reduces the level of circulating leucocytes. This decreases the adherence of neutrophils to the vascular endothelium in turn theses effects reduce the incidence of pain episodes and acute chest syndrome episodes.