[Thermostability testing of iron(II) sulphate for formulation of drug product]

The aim of the experimental study was to determine which iron(II) sulphate form, the monohydrate or the heptahydrate, is more suitable for formulation of a retard dosage form with melt technology, and to control the suitable compound from a thermostability aspect according to the ICH (International Conference on Harmonization). Iron(II) sulphate is susceptible to oxidation and a rise in temperature increases the rate of this redox change. The presence of Fe3+ is definitely harmful in the case of enteral administration. First, the activation energy of the oxidation process was quantified for both iron(II) sulphate forms. It was found that the monohydrate is oxidized four times more slowly than the monohydrate form. It follows from this that the monohydrate well resists short-lived high temperature. The thermostability tests on the monohydrate showed that samples, stored at high temperature and high relative humidity for a long time, oxidized only slowly. On the basis of all these findings, the monohydrate form may be suggested for melt technology.