Bioavailability of iron in oral ferrous sulfate preparations in healthy volunteers

The bioavailability of iron in five ferrous sulfate preparations was studied in 10 healthy male volunteers. The preparations were an oral solution, two types of film-coated tablets and two types of enteric-coated tablets. Blood samples were drawn hourly from 8 am to 6 pm on the day before each study day to assess baseline serum iron concentrations and on the study day. Spectrophotometry was used to measure the serum iron concentrations. The area under the curve (AUC), the maximum concentration and the time to achieve the maximum concentration were compared by analysis of variance. The enteric-coated preparations resulted in AUCs less than 30% of the AUC for the oral solution. The two film-coated products produced AUCs essentially equivalent to that of the oral solution. We conclude that the bioavailability of iron in the enteric-coated preparations was low, relative to that of the film-coated products and the oral solution, and that these products should not be considered interchangeable.