Massive doses of iron (from 0.608 to 1.32 Gm. as colloidal terric hydroxide or colloidal ferric oxide) were given intravenously in single infusions to 8 different patients with hypochromic microcytic anemia. One patient was given a second injection after an interval of four months, so that nine administrations were made. The following observations were made:

1. The reticulocyte response was higher in each instance than would be expected in oral therapy. In 3 additional patients in whom injection had to be discontinued after 0.070, 0.180, and 0.123 Gm. of elemental iron had respectively been given, the reticulocyte rises were higher than were the average responses reported by Heath18 after optimal oral therapy. This at least suggests that "optimal" oral therapy does not provide a maximal stimulus to outpouring of reticulocytes from the bone marrow. Comparable doses of iron given to 3 control subjects with normal hemoglobin levels did not cause a reticulocytosis.

2. The average rate of hemoglobin regeneration per 100 cc. of blood per day was 0.224 Gm.; the lowest value was 0.16 Gm. and the highest 0.27 Gm. These figures were calculated for the rise that occurred from the day of iron administration to the time at which the rate of hemoglobin increase was obviously becoming slower. Since correction was not made for blood loss in 3 of the patients during the period of regeneration, the figures for the rate of hemoglobin formation are lower than they otherwise would have been. Even so they are distinctly greater than those usually obtained following oral therapy (table 2), but no greater than is found in an occasional patient given iron by mouth. The data suggest that the fastest rate of hemoglobin regeneration that can be stimulated by iron in subjects with hypochromic anemia approximates 0.3 Gm. per 100 cc. per day.

3. Calculations indicated that from 71.8 to 99.7 per cent of the injected iron was apparently used for the synthesis of hemoglobin. These figures are likewise lower than they would have been if several of the patients had not lost blood during the recovery period. The observation of other workers that parenterally administered iron is almost completely retained by the body and converted into hemoglobin was therefore confirmed.

4. Toxic reactions to the injected iron are described in detail. They were severe in all but two instances, and in 3 patients were so alarming that injection of iron had to be discontinued. There can be no doubt that the reactions to iron parenterally administered in large doses are great enough to contra-indicate use of this measure as a therapeutic procedure.

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