Comparison of free iodine as a function of the dilution of two commercial povidone-iodine formulations.

Binding studies by means of equilibrium dialysis on two different Povidone-lodine-solutions reveal that the amount of available iodine and free iodine is very different as such and after dilution. The free iodine concentration in the Braunol concentrate was found to be ca. 22 mg/L and in the iso-Betadine concentrate only ca. 2.1 mg/L, despite the total amount of available iodine in iso-Betadine being higher than that of Braunol. As the bactericidal level of free iodine is characterised by concentrations >5 ppm, Braunol can be employed as a disinfectant as such, iso-Betadine has to be diluted before use. In both concentrates more than 99% of available iodine is present as reservoir for free iodine. Concerning the results as a function of dilution, it was demonstrated that, for both solutions, free iodine reaches a maximum after a 50-fold dilution (ca. 31 mg/L and ca. 51 mg/L for iso-Betadine and Braunol respectively). After dilution, a more constant level of free iodine was observed in the Braunol than in the iso-Betadine solution, and this is attributed to the present molar ratio of I(2)/I- and the addition of iodate in the former. The pH for both solutions approximates that of the skin, as such and after dilution. In summary, it can be stated that Braunol is superior to iso-Betadine as to the release of free iodine in both the undiluted as well as in the diluted form.