Shellac

Scientific Name(s): Laccifer lacca . Family: Coccidae

Common Name(s): Shellac , lac , gommelaque , lacca

Uses

The most common use is as a furniture finish, but it has also been used in the pharmaceutical industry, in dentistry, and in cosmetics.

Dosing

There is no clinical evidence to support specific doses of shellac for therapeutic purposes.

Contraindications

Contraindications have not yet been identified.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

None well documented.

Adverse Reactions

Little data are available. One report discusses contact cheilitis.

Toxicology

Shellac NF is food grade and is listed as Generally Recognized as Safe (GRAS) by the FDA.

Shellac is the purified product of lac, the red, hardened secretion of the insect Laccifer (Tachardia) lacca Kerr. This tiny insect sucks the sap of selected trees and bushes, and secretes lac as a protective covering. The name lac is said to derive from lakh , the Sanskrit word for one hundred thousand, a reference to the very large number of insects involved in producing appreciable amounts of the product. 1

Lac is cultivated in India, Thailand, and Burma. The whitest lac is produced by insects infesting the kusum tree ( Schleichera trijuga ). The harvester cuts twigs coated with lac into small pieces called sticklac. The crude material is ground and soaked in water to remove debris and insect bodies. The remaining material is soaked in sodium carbonate, which removes laccaic acid, a complex mixture of at least four structurally related pigments. The resulting granules retain the yellow pigment erythrolaccin and are dried to form seedlac. Further treatment by melting, evaporating, or filtering yields shellac. 2

Chemistry

The National Formulary XV recognizes 4 grades of shellac: Orange, dewaxed orange, regular bleached and refined wax-free bleached. The grades differ in the manner in which the seedlac is treated. Orange shellac is obtained by the evaporation of filtered ethanolic solutions of seedlac. It may be dewaxed by further filtration. Regular bleached shellac is obtained by dissolving the seedlac in aqueous sodium carbonate at a high temperature. After filtration, a bleaching agent (such as sodium hypochlorite) is added. The resin is removed by sulfuric acid precipitation. Refined wax-free bleached shellac adds another filtration step to remove the waxes. 3

The exact chemical composition of shellac is unknown. It appears to be composed of a network of hydroxy fatty acid esters and sesquiterpene acid esters with a molecular weight of about 1000. Aleuretic acid, r-butolic acid, shellolic acid, and jalaric acid are the major constituents. The composition is a function of the source and time of harvest of the sticklac. Variability in the product may be a problem for commercial users of shellac. The physical properties of shellac also vary. For example, the reported melting point ranges from 77° to 120°C. Shellac is soluble in ethanol, methanol, glycols, glycol ethers, and alkaline water. 1

Uses and Pharmacology

Shellac is most often used as a finish for fine furnitures. Further, the material has been used for almost 100 years by the pharmaceutical industry. Examples of shellac's role in this field include: Tablet coating formulations, 4 , 5 , 6 , 7 microencapsulation, 8 , 9 , 10 , 11 , 12 matrix formation, 13 enteric coating, 14 humidity tolerance, 15 and binding ability. 16 However, shellac undergoes an “aging effect” upon storage and thus has fallen into disfavor as an ingredient in some preparations. 2

Dentistry has also used shellac in various ways. 17 , 18 Reported uses include binding agents for dentures, restorations, and mouldings and as a constituent in “artificial calculus” for training purposes in dental schools. 19 , 20 , 21 , 22 , 23

Shellac has also been used as an ingredient in hair spray 24 and in other cosmetics 25 and as pretreatment against mushroom toxins in mice. 26

Dosage

There is no clinical evidence to support specific doses of shellac for therapeutic purposes.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

None well documented.

Adverse Reactions

One report discusses contact cheilitis to shellac. 27 Another report reviews bezoars (accumulations of foreign material in the stomach) such as shellac. This unusual collection in the GI tract, if untreated, may lead to anorexia, weight loss, bleeding, or perforation. 28

Toxicology

Little data are available regarding toxicity. One study investigated the short-term inhalation toxicity in rabbits of a hair spray-containing shellac; the product did not induce any significant toxicologic problems. 29 Shellac NF is food grade and is listed as Generally Recognized as Safe (GRAS) by the FDA.

Bibliography

1. Yates P, Field GF. Tetrahedron. 1970;26:3135.
2. Der Marderosian A. Natural Product Medicine. Philadelphia, PA: George F. Stickley Co. 1988;356–57.
3. Pharmaceutical Glazes, Bulletin 70-09-01, William Zinsser and Co.
4. Pandula E, et al. Acta Pharm Hung 1970 Jan;40:25–28.
5. Alam A, et al. J Pharm Sci 1972 Feb;61:265–68.
6. Tuerck P, et al. J Pharm Sci 1973 Sep;62:1534–37.
7. Sheorey D, et al. Indian J Pharm Sci 1992;54(5):169–73.
8. El Banna H, et al. Pharm Indus 1982;44(6):641–45.
9. Labhasetwar V, et al. J Microencapsul 1989;6(1):115–18.
10. Labhasetwar V, et al. J Microencapsul 1990:7(4):553–54.
11. Sheorey D, et al. Int J Pharm 1991 Feb 1;68:19–23.
12. Sheorey D, et al. J Microencapsul 1991;8(3):375–80.
13. Serajuddin A, et al. J Pharm Sci 1984 Sep;73:1203–8.
14. Chang R, et al. Int J Pharm 1990 Apr 30;60;171–73.
15. Gursoy A, et al. Pharmazie 1986;41(8):575–78.
16. Labhasetwar V, et al. Indian J Pharm Sci 1988 Nov-Dec:50:343–45.
17. Azouka A, et al. J Oral Rehabil 1993;20(4):393–400.
18. Harrison A, et al. J Oral Rehabil 1995;22(7):509–13.
19. Lie T, et al. J Clin Periodontal 1987;14(3):149–55.
20. Escoe R. Int J Prosthodon 1989;2(3):243–44.
21. Hitge M, et al. Ned Tijdschr Tandheelkd 1989;96(8):372–77.
22. Lee C, et al. J Pros Dent 1991;66(5):623–30.
23. Heath J, et al. J Oral Rehabil 1993;20(4):363–72.
24. Tannert U. Seifen, Oele, Fette, Wachse 1992 Oct 30;118:1079–80.
25. Penning M. Seifen, Oele, Fette, Wachse 1990 Apr 5;116:221–24.
26. Adams W, et al. J Pharmacol Exp Ther 1989;249(2):552–56.
27. Rademaker M, et al. Contact Dermatitis 1986;15(5):307–8.
28. Andrus C, et al. Am J Gastroenterol 1988;83(5):476–78.
29. Monograph on Shellac, Informatics Inc., Rockville MD, 1978, PB-287-765.

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