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The bioavailability of iron on Fe(III)-hydroxide-polymaltose complex was compared intraindividually with that of Fe (II)-ascorbate (iron absorption) and a Fe (II)-sulphate quick release preparation (haemoglobin regeneration test). The study was carried out in a population of 16 healthy male volunteers, phlebotomized in weekly intervals until development of an iron deficiency anaemia in order to establish a test population with only small variations of their individual body iron status. Intestinal iron absorption in fasting state as measured by 59Fe whole body retention and simultaneous estimation from plasma iron tolerance curves was low for the 59Fe (III)-complex (1.2 +/- 0.1% (means +/- SD] as compared to the 59Fe (II)-ascorbate (43.7 +/- 7.1% (means +/- SD]. Iron administration together with a test meal did not affect the absorption from the 59Fe (II)-ascorbate, whereas the 59Fe (III)-complex showed a significant increase in absorption (8.8 +/- 4.7% (means +/- SD]. Haemoglobin (Hb) regeneration after 100 mg of iron as Fe (III)-complex and Fe (II)-sulphate administered during 28 days with meals amounted to a mean of 0.68 +/- 0.2 g/l and 1.1 +/- 0.3 g/l (means +/- SD) of total daily Hb-increase and a net-Hb-increase of 0.31 +/- 0.37 g/l and 0.79 +/- 0.36 g/l (means +/- SD), respectively. There was also a small but significant rise in serum ferritin during the oral treatment in both treatment groups. The results of Hb-regeneration after treatment with the Fe (III)-complex were in the range which could be expected from the absorption measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Since 1977 the bioavailability of 14 bi- and trivalent oral iron preparations has been investigated in five separate orientated clinical studies by using postabsorption serum iron concentration curves. The range of relative bioavailability was 46 to 100% in the first group of preparations, 31 to 47% in the second group and 6 to 29% in the third group. The first group contained mainly bivalent quick release preparations, the second group slow or sustained release preparations and the third mainly trivalent iron preparations. The postabsorption serum iron concentration curves which show a good congruence with exact 59Fe whole body retention tests again confirmed the nearly 50-year-old rule that bivalent iron is up to 16 times better absorbed than trivalent iron. There is no doubt that the oral iron preparations of good bioavailability are able to cure an iron deficiency more rapidly than iron preparations with a low bioavailability. This therefore has a clear influence on the overall expense of iron therapy. Only those preparations from the first group can be recommended for oral iron therapy. The preparations in the second group are less suitable and those in the third group should be excluded from iron therapy in all countries.

Commercial oral iron preparations (drops) containing trivalent iron either as a citrate (C) or hydroxide-polymaltose complex (HP) were labelled with 59Fe in the thermal neutron flux of a research reactor. No measurable differences were observed between the original commercial preparation and the neutron-activated samples. In an intraindividual comparison oral doses of 100 mg 59Fe were administered as an aqueous 59Fe(II)-ascorbate solution (= reference), C (-59Fe) and HP (-59Fe) to starved subjects with normal and depleted iron stores. Two weeks later the whole body retention of absorbed 59Fe was measured and used for the calculation of 59Fe-absorption. Subjects with normal Fe-stores absorbed means a +/- SEM +/- SD = 8.53 +/- 0.29 +/- 1.2% of the 59Fe from the aqueous 59Fe(II)-ascorbate solution, 1.58 +/- 0.12 +/- 0.49 of the C-59Fe and 0.81 +/- 0.06 +/- 0.27% of the HP-59Fe. Subjects with depleted Fe-stores absorbed means a +/- SD = 17 +/- 3% of the 59Fe from the aqueous 59Fe(II)-ascorbate solution and only 2.4 +/- 1% from the HP-59Fe. The relative bioavailabilities were reduced from 100% (reference = Fe(II)-ascorbate) to 19% for the C-Fe and to 9.5% for the HP-Fe in subjects with normal Fe-stores. In subjects with depleted iron stores the relative bioavailability was decreased from 100 to 14% for the HP-Fe. Oral iron preparations with a relative bioavailability less than 10% or less than 30% are considered to be therapeutically ineffective or insufficient, respectively.

The value of a medicinal iron preparation is influenced by several factors e.g. therapeutical efficacy, frequency of side effects, and prescriptions for intake. Since the accurate quantitation of therapeutical efficacy is difficult to establish, the value of fractional intestinal absorption of iron, which is a prerequisite for the effect on haemoglobin regeneration, represents a useful criterion for that particular factor. When intestinal absorption is investigated the selection of subjects is of importance. Studies should be performed on subjects with iron deficiency since the adaptation of intestinal absorption to the body's need is the basis of oral iron supplementation. Different methods have been used to assess intestinal absorption, some of which give almost identical results or show a close correlation. However, mixing data from different investigations in order to convert semi-quantitative values obtained from plasma iron tolerance curves into amounts of absorbed iron by means of regression equations estimated from studies on different subjects and under different conditions may lead to considerable uncertainties of the calculated results. Even more difficult to evaluate is the relation between fractional absorption and costs of therapy, since there are additional factors influencing the duration of supplementation and therefore the total amount of iron necessary.