Human pharmacokinetics and safety of boric acid

Using an in vitro technique it has been demonstrated that water-emulsifying and hydrophobic ointments containing boric acid liberate only minute amounts (1-6%) within 24 h compared with the nearly total liberation from a jelly. When an amount of boric acid containing ointment is swallowed, the absorption is only slightly delayed compared with a similar intake when dissolved in water, and in both cases nearly total excretion is found in the urine within 96 h. The halflife (t 1/2 beta) is 21 h (mean, 7 adult men). The pharmacokinetics rule out the risk of cumulative poisoning with topical preparations containing low amounts of boric acid. The use of water-emulsifying ointments containing up to 3% boric acid should be safe, even for repeated daily use in the napkin region.