Effects of erythropoietin therapy on iron absorption in chronic renal failure

Abstract

The effect of erythropoietin administration on the absorption of dietary and therapeutic iron was examined in patients with anemia of chronic renal failure on maintenance hemodialysis. Absorption from test meals tagged extrinsically with iron 55, iron 59, or both was determined 2 weeks later by using incorporated red blood cell radioactivity and whole body counting. In an initial study of food iron absorption, the effect of initiating erythropoietin therapy was determined by measuring the absorption of heme and nonheme iron before and 2 weeks after the administration of 64 U/kg body weight erythropoietin (range, 46-85 U/kg body weight) three times weekly. Absorption of heme iron increased 1.6-fold from 18.6% to 30.1% (P <.05), and nonheme iron increased 3.7-fold from 1.3% to 4.9% (P <.01) after erythropoietin therapy. In a second study therapeutic iron absorption was evaluated at baseline and after erythropoietin administration (63 U/kg body weight [range, 48-74 U/kg body weight] three times weekly). The absorption of 50 mg of iron as ferrous sulfate increased 2.4-fold from 3.8% to 9.4% (P <.05) when given without food and 4.2-fold from 1.4% to 5.9% (P <.05) when given with food after erythropoietin administration. After adjusting for changes in iron stores with serum ferritin after erythropoietin therapy, the enhanced erythropoiesis associated with erythropoietin therapy increased absorption about 2-fold, which was similar to the response observed previously in normal subjects. In a final study we examined the absorption of therapeutic iron during the steadystate phase of erythropoietin therapy after an erythroid response to erythropoietin had occurred. The absorption of 50 mg of iron was lower than that occurring with the initiation of erythropoietin therapy at 2.2% when given alone and 1.3% when taken with food. We conclude that iron absorption with or without erythropoietin stimulation is unimpaired in patients with chronic renal failure. (J Lab Clin Med 2000;135:452-58)