Boric Acid

1 Nonproprietary Names Table I: Pharmacopeial specifications for boric acid.

BP: Boric acid Test JP 2001 PhEur 2005 USPNF 23
JP: Boric acid
PhEur: Acidum boricum Identification þ þ þ
USPNF: Boric acid Appearance of þ þ —
solution
Loss on drying 40.50% — 40.50%
2 Synonyms Sulfate — 4450 ppm —
Heavy metals 410 ppm 415 ppm 40.002%
Boracic acid; boraic acid; Borofax; boron trihydroxide; E284; Organic matter — þ —
orthoboric acid; trihydroxyborene. Arsenic 45 ppm — —
pH — 3.8–4.8 —
Solubility in alcohol — þ þ
3 Chemical Name and CAS Registry Number Assay 499.5% 99.5–100.5% 99.5–100.5%
Orthoboric acid [10043-35-3]
Metaboric acid [13460-50-9]
10 Typical Properties
Acidity/alkalinity: pH = 3.5–4.1 (5% w/v aqueous solution)
4 Empirical Formula and Molecular Weight Density: 1.435
H3BO3 61.83 (for trihydrate) Melting point: 170.98C. When heated slowly to 181.08C, boric
HBO2 43.82 (for monohydrate) acid loses water to form metaboric acid (HBO2); at 1408C,
tetraboric acid (H2B4O7) is formed; and at higher tempera-
tures, boron trioxide (B2O3) is formed.(12)
5 Structural Formula Solubility: miscible with ethanol, ether, glycerin, water, and
other fixed and volatile oils. Solubility in water is increased
H3BO3 by addition of hydrochloric, citric, or tartaric acids.
Specific gravity: 1.517

6 Functional Category
11 Stability and Storage Conditions
Antimicrobial preservative.
Boric acid is hygroscopic and should therefore be stored in an
air-tight, sealed container. The container must be labeled ‘Not
for Internal Use’.
7 Applications in Pharmaceutical Formulation
or Technology
12 Incompatibilities
Boric acid is used as an antimicrobial preservative in eye
drops,(1,2) cosmetic products,(3) ointments,(4,5) and topical Boric acid is incompatible with water, strong bases and alkali
creams.(6) It is also used as an antimicrobial preservative in metals. It reacts violently with potassium and acid anhydrides.
foods. It also forms a complex with glycerin, which is a stronger acid
Boric acid has also been used therapeutically in the form of than boric acid.
suppositories to treat yeast infections,(7–9) and in dilute
concentrations as a mild antiseptic, although it has been
superseded by more effective and less toxic disinfectants.(10) See 13 Method of Manufacture
Section 14. Boric acid occurs naturally as the mineral sassolite. However,
Boric acid and borate have good buffering capacity and are the majority of boric acid is produced by reacting inorganic
used to control pH; they have been used for this purpose in borates with sulfuric acid in an aqueous medium. Sodium
external preparations such as eye drops.(11) borate and partially refined calcium borate (colemanite) are the
principal raw materials. When boric acid is made from
colemanite, the fine-ground ore is vigorously stirred with
8 Description mother liquor and sulfuric acid at about 908C. The by-product
calcium sulfate is removed by filtration, and the boric acid is
Boric acid occurs as a hygroscopic, white crystalline powder,
crystallized by cooling the filtrate.
colorless shiny plates, or white crystals.

14 Safety
9 Pharmacopeial Specifications
Boric acid is a weak bacteriostatic and antimicrobial agent, and
See Table I. has been used in topical preparations such as eye lotions,
 Boric Acid 75

mouthwashes and gargles. It has also been used in US- and 18 Comments
Japanese-approved intravenous products. Solutions of boric
Boric acid has been used experimentally as a model oxo-acid to
acid were formerly used to wash out body cavities, and as
retard mannitol crystallization in the solid state.(16)
applications to wounds and ulcers, although the use of boric
The EINECS number for boric acid is 233-139-2.
acid for these purposes is now regarded as inadvisable owing to
the possibility of absorption.(13) Boric acid is not used internally
owing to its toxicity. It is poisonous by ingestion and 19 Specific References
moderately toxic by skin contact. Experimentally it has proved 1 Kodym A, Marcinkowski A, Kukula H. Technology of eye drops
to be toxic by inhalation and subcutaneous routes, and containing aloe (Aloe arborescens M–Liliaceae) and eye drops
moderately toxic by intraperitoneal and intravenous routes. containing both aloe and neomycin sulphate. Acta Pol Pharm
Boric acid is absorbed from the gastrointestinal tract and 2003; 60(1): 31–39.
from damaged skin, wounds, and mucous membranes, 2 Tromp TFJ, Nusman-Schoterman Z, et al. Preservation of eye
although it does not readily permeate intact skin. The main drops. Pharm Weekbl 1975; 110(465–472): 485–492.
symptoms of boric acid poisoning are abdominal pain, 3 Seller R, Caldini O, Orzalesi G, et al. Preservation of cosmetic
diarrhea, erythematous rash involving both skin and mucous products: protection of the talc powders. Boul Chim Farm 1974;
membrane, and vomiting. These symptoms may be followed by 113(Dec): 617–627.
4 Allen LV, Stiles ML. Compound’s corner: diaper rash paste.
desquamation, and stimulation or depression of the central Maryland Pharm 1986: 62(Dec): 30.
nervous system. Convulsions, hyperpyrexia, and renal tubular 5 Dawson CR, Daghfous T, Whitcher J, et al. Intermittent trachoma
damage have been known to occur. chemotherapy: controlled trial of tetracycline or erythromycin.
Death has occurred from ingestion of less than 5 g in young Bull World Health Organ 1981; 59: 91–97.
children, and of 5–20 g in adults. Fatalities have occurred most 6 Shaw K. Vaginal yeast infections. Pharm Times 1998; 64(Dec): 57–
frequently in young children after the accidental ingestion of 58, 60.
solutions of boric acid, or after the application of boric acid 7 Allen LV. Boric acid suppositories. US Pharm 1996; 21(Jan): 92–
powder to abraded skin. 93.
The permissible exposure limit (PEL) of boric acid is 8 Van Slyke KK, Michel VP, Rein MF. Treatment of vulvovaginal
candidaisis with boric acid powder. Am J Obstet Gynecol 1981;
15 mg/m3 total dust, and 5 mg/m3 respirable fraction for 141: 145.
nuisance dusts.(14) 9 Allen ES. Multiple-ingredient drug for use in the treatment of
LD50 (mouse, oral): 3.45 g/kg(15) vaginitis. Clin Med 1971; 78: 31–32.
LD50 (mouse, IV): 1.24 g/kg 10 Sweetman SC, ed. Martindale: The Complete Drug Reference,
34th edn. London: Pharmaceutical Press, 2005: 1662.
LD50 (mouse, SC): 1.74 g/kg 11 Lund W, ed. The Pharmaceutical Codex: Principles and Practice of
LD50 (rat, oral): 2.660 g/kg Pharmaceutics, 12th edn. London: Pharmaceutical Press, 1994: 67.
LD50 (rat, IV): 1.33 g/kg 12 Lund W, ed. The Pharmaceutical Codex: Principles and Practice of
LD50 (rat, SC): 1.4 g/kg Pharmaceutics, 12th edn. London: Pharmaceutical Press, 1994:
109.
13 Zabka M, Vitkova Z, Burelova A, Mandak M. Formulation and
15 Handling Precautions local anesthetic activity of carbizocaine in collyria. Cesk Farm
1988; 37(10): 457–460.
Observe normal precautions appropriate to the circumstances 14 Dean JA, ed. Lang’s Handbook of Chemistry, 13th edn. New York:
and quantity of material handled. Boric acid is irritating to the McGraw-Hill, 1985: 4–57.
skin and is potentially toxic by inhalation. Gloves, eye 15 Lewis RJ, ed. Sax’s Dangerous Properties of Industrial Materials,
protection, protective clothing, and a respirator are recom- 11th edn. New York: Wiley, 2004: 536.
mended. 16 Yoshinari T, Forbes RT, York P, et al. Crystallisation of amorphous
mannitol is retarded using boric acid. Int J Pharm 2003; 258: 109–
120.
16 Regulatory Status
Accepted for use as a food additive in Europe. Included in the 20 General References
FDA Inactive Ingredients Guide (IV injections; ophthalmic —
preparations; otic solutions; topical preparations). Reported in
the EPA TSCA Inventory. In the UK, the use of boric acid in
cosmetics and toiletries is restricted. Included in the Canadian 21 Authors
List of Acceptable Non-medicinal Ingredients. M Yelvigi.

17 Related Substances 22 Date of Revision

Sodium borate. 15 August 2005.