[Liberation and in vitro skin permeation of boric acid from an ointment]

In connection with the discussion on a uniform regulation within the European Communities for baby-care products containing boric acid, it was of interest to which degree boric acid can be absorbed through normal or damaged skin from a common baby ointment. Studies performed by an in vitro permeation method using excised human skin and by a liberation method in the absence of a membrane are described. Boron was not detectable in the acceptor compartment when intact skin was tested, while using damaged skin, prepared by removing the horny layer, a maximum permeation of 2.46 micrograms/cm2 boron, corresponding to 14.1 micrograms/cm2 boric acid, was measured. Accordingly the stratum corneum functions as an effective barrier for the cutaneous permeation of boric acid under the given conditions. Thus there is no cause for concern that the ointment under consideration could evoke unwanted systemic effects when applied to healthy skin. The results showing permeation of boric acid through damaged skin are of special interest, since it has to be taken into account, that skin care preparations for babies may be applied on irritated skin, e.g. in cases of napkin dermatitis. On the basis of the permeation results for damaged skin the possible daily boron uptake of babies, treated with the test product, is estimated and compared to the daily alimental intake of boron. With respect to quantities of boric acid delivered per unit of surface in the skin model and in the liberation system, the permeation through damaged skin amounts to 86% of the release. The results indicate, that the degree of permeation through damaged skin depends on the degree of liberation from the vehicle. The liberation model presented here could be suitable for the assessment to which extent boric acid may be absorbed from an ointment through damaged skin in worst case.