Hydroxyurea increases the production of fetal hemoglobin (hemoglobin F) in patients with sickle cell anemia and therefore has the potential for alleviating both the hemolytic and vaso-occlusive manifestations of the disease. There is preliminary evidence that recombinant human erythropoietin may also increase hemoglobin F production.

We treated five patients with sickle cell disease with escalating doses of intravenous erythropoietin for eight weeks. Three of these patients were subsequently treated with daily doses of oral hydroxyurea. After the optimal dose was determined, erythropoietin was then given along with hydroxyurea for four weeks.

Treatment with erythropoietin, either alone or in combination with hydroxyurea, had no significant effect on the percentage of hemoglobin F—containing reticulocytes (F reticulocytes) or red cells (F cells). In contrast, hydroxyurea treatment was associated with a 3-to-25-fold increase in F reticulocytes, a 1.6-to-7-fold increase in F cells, and a 2.3-to-16-fold increase in the percentage of hemoglobin F. In all three patients given hydroxyurea, treatment with this drug was associated with reduced hemolysis, shown by decreases in serum bilirubin and lactic dehydrogenase and prolongation of red-cell survival. Hydroxyurea treatment also resulted in a decrease in the percentage of irreversibly sickled cells and sickling at partial oxygen saturation, an increase in oxygen affinity and total red-cell cation content, and a reduction in potassium-chloride cotransport. All three patients had a decrease in the number of pain crises.

This study confirms that hydroxyurea therapy increases hemoglobin F production and provides objective evidence that hydroxyurea reduces the rate of hemolysis and intracellular polymerization of hemoglobin S. In contrast, recombinant human erythropoietin, whether alone or in combination with hydroxyurea, offers no measurable benefit. (N Engl J Med 1990; 323:366–72.)