[Bioavailability of iron in oral iron preparations. Principles of duration and dosage (author's transl)].MMW Munch Med Wochenschr. 1979 Aug 31; 121(35):1104-8.MM
Using 59Fe labeled iron preparations, both the exactly and quantitatively determined absorbability by whole body retention measurement of the absorbed 59Fe and the calculated relative bioavailability from the postabsorption rise in serum iron concentration have coincidently shown that only about half as much Fe (II) is absorbed from oral iron preparations with delayed liberation of iron in the small intestine than from an Fe (II) preparation liberating Fe (II) more rapidly in the stomach. From preparations with trivalent iron only 1/7 to 1/20 of the amount of iron is absorbed which can be absorbed from an Fe (II) preparation with a more rapid rate of Fe liberation. The optimal oral iron therapy is therefore with aqueous solutions of Fe (II) or Fe (II) preparations which disintegrate immediately in the stomach.