Percutaneous Absorption of Boric Acid from Boron‐Containing Preparations in Rats

Abstract

An aqueous jelly and two oleaginous ointments containing less than 3 % boric acid wlv, were applied on the skin of anaesthetized rats. When application was made on the intact skin of the dorsal surface (about 28 cm2) determination of boric acid concentrations in the urine 8 hours later showed no or slight increases above the normal level. When the skin was damaged the ointments caused increased excretion up to 4-8 times that of the excretion found in control animals, while the jelly caused a 34 times increase. When an enclosed skin area of 4.3 cm2 was damaged and treated, and simultaneous recording of boric acid recovery in both the urine and applied preparations (jelly and one ointment) was made 5 hours later, about 98 % boric acid still remained in the ointment, but only 25 % in the jelly. The recoveries in the urine were 1 % and 25 % respectively, indicating slight absorption and rapid excretion in the case of the oleaginous ointment, and high absorption with inadequate excretion when the aqueous jelly was applied.

Effect of Boron on Sympathetic Skin Response in Rats

“…When applications of boric acid to intact and damaged skin were compared, the concentration in urine was 34 times higher in jelly form and 4 to 8 times higher in ointment form. [ 30 ] In another study, the water-based jelly form of boric acid caused increased boron levels in the blood and urine levels of infants. [ 31 ] In addition, no increase in the plasma level of boron was observed after the topical application of boric acid ointment to the napkin-covered area.…”

Borsäure [MAK Value Documentation in German language, 1991]

“…B. Wasser-Öl-Emulsionen) dagegen leicht verzögert [7,8]. Durch intakte Haut von Mensch und Tier (Kaninchen) wird Borsäure nur geringfügig resorbiert, unabhängig davon, ob die Applikation als Pulver [11], als wasserfreie Salbe [12,13], als konzentrierte wäßrige Lösung [6, 11, 14�18] oder als Talkumpuder [11, 17�20] erfolgt; dasselbe gilt auch bei Applikation an der Vaginalschleimhaut [21,22]. Daß die intakte Hornschicht eine wirksame Barriere gegen die perkutane Permeation von Borsäure darstellt (37 °C, 4 Stunden, aus wasserfreier Salbengrundlage), konnte auch in vitro an intakter menschlicher Abdominalhaut bestätigt werden, wobei Borsäure im Akzeptormedium nicht nachzuweisen war [23].…”