Boric acid vaginal suppositories: a brief review.

STRUCTURE AND DERIVATION oric acid, also called boracic acid or orthoboric acid, is an inorganic acid with the chemical formula H3BO3. It is available as a white, odorless powder and in crystalline and granular forms. Bo-ric acid vaginal suppositories are not commercially available and, therefore, must be compounded. Most studies documenting efficacy utilize 600 mg of boric acid powder in a gelatin capsule, although other extemporaneous formulations have been developed , Boric acid is a weak, topical, bacteriostatic, and fun-gistatic agent; however, the exact mechanism of action is unclear. 4 It has been suggested that the fungistatic activity may be mediated by vaginal acidification, resulting in fungal cell wall penetration and disruption of the fungal cell membrane. 5 Conversely, studies evaluating the minimum in-hibitory concentration of boric acid indicate that boric acid works at a pH similar to that of the untreated vaginal tract, and, therefore, the action may not be simply due to an increase in acidity. 6,7 PHARMACOKINETICS Boric acid is rapidly and completely absorbed following oral ingestion and is well absorbed through denuded and abraded skin in solution or as a dry powder. 8 Absorption has been reported to be negligible through intact skin in the presence of alkaline salts. 9 Once absorbed, boric acid is widely distributed throughout body water and accumulates in the brain, liver, and kidneys. 8 Boric acid is not appreciably metabolized and is primarily excreted unchanged by the kidneys, with about 50% excreted within twelve hours of administration 1 and 90% of excretion occurring within 96 hours, a Minimal amounts are excreted in feces, sweat, and saliva, a In a study evaluating vaginal absorption of boric acid following the intravaginal administration of one to two 600-mg boric acid capsules for one to two weeks in eight healthy volunteers, daily blood boron concentrations of less than lag/mL during use (mean level, 42 pg/mL) were reported, lz No volunteer had detectable boric acid levels 48 hours after the end of treatment. Boron blood levels below 200 pg/mL are thought to be safe by many investigators, with normal blood boron levels ranging from 0.1 to 80 lag/mL. z'a3 Blood boron analysis following vaginal insertion of a single 600-mg boric acid capsule in one healthy volunteer revealed sys-temic boric acid absorption of approximately 6% from the vagina and a serum half-life of about 10.5 hours. 7 A half life of 21 hours has been reported following …