CA1319875C - Fatty acid stabilized aqueous aerosol foams - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An essentially monohydric alcohol free com-position able to form a foam. The composition has a propellant, water and a fatty acid. The components are present in ratios that prevent their separation.

Description

131987~

This invention relates to a composition able to form a foam. The invention permits the production of stabilized, homogeneous, aqueous aerosol foams having good shelf-life and the ability to dissolve inorganic compounds, good potability and easily alterable foaming characteristics. In a preferred embodiment the inven-tion includes a therapeutically useful ingredient, par-ticularly an ingredient useful in dentistry.

The uptake of fluoride ions by dental enamel increases its resistance to acids and dissolution. This has been shown in many clinical trials, which have shown a decrease of dental cavities from the use of soluble fluorides. The local application of high fluoride con-tent solution or gel at regular intervals, under the supervision of trained dental practitioners, is a simple, economical method of applying a fluoride; it is usually referred to as topical application. In this procedure patients are given small plastic trays conforming in shape to the dental arch that are filled with gels con-taining 1.23~ fluoride ion. Under supervision the patient sits for a few minutes with the gel in contact with the teeth. The tray and the gel are then removed followed by a rinsing of the mouth. This technique _l_ 131987~

causes excessive salivation, particularly in children, with subsequent inadvertent swallowing of the fluoride containing gel components. In an attempt to avoid this it is common to insert a suction tube to remove both the gel and excess saliva from the mouth. However, this technique does not work well with children.

It is considered of increasing importance in dental health schemes to identify children prone to caries. It is said that 20~ of the child population has 80~ of dental cavities, thus indicating the wisdom of identification of these children. It is proposed to follow such identification by monthly application of fluoride in the topical application fashion described above. However, this means that there exists a reaso-nable possibility that such children could be overdosed with ingested fluoride over a period as short as a year.

The generation of foams is well known.
Similarly the use of propellents and aerosol containers is well known but the prior art has not been able to pro-duce physically and chemically stable, aqueous and potable foams that can be delivered using conventional propellents and aerosol containers and that do not foul, plug or damage aerosol container components. In addition the prior art has failed to demonstrate how inorganic 131987~

salts, for example, sodium fluoride, can be dissolved in a solution of aerosol propellent and water without component separation in the aerosol container. For example, foamable toothpastes, have been found to plug aerosol container orifices due to their extremely high abrasives content. In addition formulations containing sodium lauryl sulphate and sodium fluoride have been found to attack metal aerosol containers with formation of poisonous hydrogen sulphide gas. The inventors have also observed that compositions having high abrasives content are not physically stable, that is will not produce a homogenuous, lasting foam. They are not suitable for a topical application without brushing and have poor rheological or flow characteristics.

The present invention therefore seeks to provide a composition that will produce a desirable foam, particularly for use in dentistry. The composition has the virtue of being able to contain compounds that are insoluble in simple alcohols, notably ethanol, present in prior art foam formulations. In particular, the com-position may contain inorganic compounds.

Accordingly, the present invention provides a composition able to form a foam and comprising the components:

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(a) a propellant and (b) water; and a free fatty acid, the components being present in ratios that prevent their separation.

In a preferred embodiment the foam further includes a therapeutically useful ingredient, particularly an ingredient useful in dentistry. Such ingredients include inorganic compounds, for example sodium fluoride, who~e use in applying fluoride to the teeth is well established, and a benzoate, for example, sodium benzoate. Sodium benzoate has anti-bacterial and anti-fungal properties so that a foam containing this compound can be useful as a mouthwash.

Preferably the water content is about 70 to 90% by weight of the composition less the propellant. The free fatty acid is about 0.2% by weight. A preferred fatty acid is myristic acid. Oleic acid is also suitable. The propellent is preferably a hydrocarbon propellant. Such propellents are well-known.

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131987~

The compositions are abrasive free homoge-neous, aqueous liquids capable of being gassed in a con-ventional aerosol container to produce, on activation of the release valve of the container, stable, potable foams. Compositions D and E contain sodium fluoride and composition F contains sodium benzoate. Compositions D
and E produce stable and potable fluoride containing foam able to reinforce dental enamel in the fashion of pre-sently used gels but with l/10 or less of the weight of intraoral material. The foam tends to dribble less, sti-mulate saliva less and is generally less messy. Storage and transport is facilitated because the weight and volume needed is 1/10 as heavy and bulky as the gels.
The fluoride component is available to the teeth as an aqueous solution, which is highly desirable for caries prevention. As the compositions are free of abrasives plugging and abrasion of aerosol container components does not take place. However, it should be emphasized that there is no absolute prohibition of abrasives.
Compounds such as sodium lauryl sulphate, which, as indi-cated above, can produce hydrogen sulphide in combination with aqueous sodium fluoride and metal cans, are pre-ferably excluded from the compositions unless plastic aerosol containers are to be used.

Composition F is suitable as a substitute for conventional mouthwashes.

~ 3198'~

The lecithin used may be that available under the trade mark Epikuron 135F from Lucas Meyer Company.
It is derived from soybean. This compound has the advan-tage of relatively low cost. However, the lecithin might also be lecithin from other sources, such as egg yokes, or indeed, any other appropriate phospholipid.

The carbopol and LDEA with Tween 80~ act as foam homogenisers. Other components present include gylcerol, cetyl alcohol and sodium dihydrogen phosphate, which are well-known in the foam art as foam homoge-neuous. Glycerol is especially suitable in this regard in the present invention.

In comparative experiments it was shown that compositions not containing free fatty acid separate during storage in every case. Aqueous foams containing myristic acid have been found to have the best shelf life and flow, that is reological, properties. None of the above foams A to F has been found to separate during pro-longed storage in transparent aerosol containers. All foams lacking the free fatty acid component were found to separate during prolonged storage in the same transparent aerosol containers.

It should be noted that in addition to the therapeutically useful sodium fluoride and sodium ben-131'.~5 zoate a wide variety of other ingredients can beincluded, for example salt such as ascorbates or sulphide anti-oxidants, disinfectants, for example Chloramine B, or medica!nent such as insulin.

PREPARATION:

A composition according to formula F above was prepared by mixing the water, sodium benzoate, carbopol and glycerol. The remaining components of composition F
were mixed and heated to form a melt. The melt was then combined with the first four components. An aerosol may be formed from this composition by adding five parts by weight of propellant A31 or A46 to 95 parts by weight of formula F. Propellants A31 or A46 are conventional hydrocarbon propellants. Fluorinated hydrocarbons, generally known as Freons~, may be used.

All of the above formulas, when combined with conventional propellants, form completely stable aqueous solutions under pressure. Formulae A to E can be pre-pared in analogous fashion to formula F. That is the lecithin and free fatty acids are always mixed together prior to the addition of water. After complete mixing of lecithin and the free fatty acid with heating to form a melt the other components, including the water, may be added as described for composition F above.

13198~

The compositions according to the present invention do not require the mechanical action of brushing or chewing to be effective, unlike dentifrices, dental creams and toothpaste, foamable or otherwise.

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Claims (21)

1. A composition able to form a foam and comprising:
(a) a propellant; and (b) water; and a free fatty acid, the components being present in ratios that prevent their separation.

2. A composition as claimed in claim 1 further including a therapeutically useful ingredient.

3. A composition as claimed in claim 2 in which the therapeutically useful ingredient is a fluoride.

4. A composition as claimed in claim 2 in which the therapeutically useful ingredient is a benzoate

5. A composition as claimed in claim 2 in which the therapeutically useful ingredient is selected from the group consisting of an antioxidant, a disinfectant and a medicament.

6. A composition as claimed in claim 1 in which the water is present in about 70% to 92% by weight of components (a) and (b).

7. A composition as claimed in claim 1 in which the fatty acid is present in an amount of about 0.2% by weight of components (a) and (b).

8. A composition as claimed in claim 1 in which the fatty acid is myristic acid.

9. A composition as claimed in claim l in which the fatty acid is oleic acid.

10. A composition as claimed in claim 1 including glycerol.

11. A composition as claimed in claim 1 including lecithin.

12. A composition as claimed in claim 1 including a foam homogeniser.

13. A composition as claimed in claim 12 in which the foam homogeniser is carbopol or, diethanol lauramide.

14. A composition as claimed in claim 1 that further includes a compound selected from the group consisting of cetyl alcohol and sodium dihydrogen phosphate.

15. A composition as claimed in claim 1 in which the propellant is an hydrocarbon.

16. A composition as claimed in claim 1 in which the propellant is about 5 parts by weight.

17. A composition able to form a foam containing a propellant and further comprising a mixture which includes:
(a) 70 -92% by weight water; and (b) about 0.2 by weight of a free fatty acid.

18. The composition of claim 17 in which the free fatty acid is selected from the group comprising myristic acid and oleic acid.

19. The composition of claim 17 wherein the mixture further includes about 2.0% by weight lecithin.

20. The composition of claim 17 wherein the mixture further includes a foam homogenizer.

21. The composition of claim 17, 18, 19, or 20 wherein the mixture further includes a therapeutically useful ingredient selected from the group comprising:
a fluoride; a benzoate; an antioxidant; a disinfectant; and a medicament.