JP7464358B2 - Emulsion composition - Google Patents

Description

The present invention relates to an emulsion composition that contains ufenamate and isopropylmethylphenol and has excellent stability of properties.

Emulsion compositions can be used to blend aqueous and oily ingredients, can be used in a variety of formulations, and have an excellent feel when applied to the skin. For this reason, emulsion compositions are widely used in the fields of topical medicines and cosmetics.

Ufenamate is used as a nonsteroidal anti-inflammatory agent in pharmaceutical or quasi-drug skin preparations for topical use. Ufenamate is a poorly water-soluble component and can be formulated as an emulsion composition. For example, Patent Document 1 describes that a skin preparation for topical use that contains a nonsteroidal anti-inflammatory agent such as ufenamate and a specific amide derivative and can be formulated in an emulsion form not only has excellent long-lasting efficacy, but also moisturizes the skin itself, has low skin irritation, is excellent in improving rough skin, and is comfortable to use.

In addition, isopropylmethylphenol has a broad range of bactericidal activity and is highly safe, and is used as an antibacterial agent in cleansers and topical skin preparations. Isopropylmethylphenol is also a poorly water-soluble component and can be formulated as an emulsion composition. For example, Patent Document 2 describes an emulsion deodorant composition containing polyether-modified silicone, (dimethicone/vinyl dimethicone) crosspolymer, 2-ethylhexyl palmitate, an antiperspirant, a bactericide, and water, in which isopropylmethylphenol is blended as a bactericide, and the composition dramatically increases the remaining ability of the bactericide to remain on the target after application.

On the other hand, lidocaine is used as a local anesthetic or antipyretic anti-inflammatory agent by being mixed into pharmaceutical or quasi-drug skin topical preparations. For example, Patent Document 3 describes an anti-inflammatory pharmaceutical composition containing tranexamic acid or its salt and a local anesthetic, and describes the use of lidocaine as a local anesthetic. Patent Document 4 describes a cooling sensation-imparting topical composition containing menthol, a medium component, and a transdermally absorbable medicinal ingredient, and describes the use of an antipyretic anti-inflammatory agent such as lidocaine as the transdermally absorbable medicinal ingredient. Patent Document 5 describes a topical composition containing a predetermined amount of at least one of an antihistamine hydrochloride and a local anesthetic hydrochloride, a predetermined amount of ethanol, a predetermined amount of borax and/or boric acid, and an organic acid and/or an organic base, and describes the use of lidocaine hydrochloride as the local anesthetic hydrochloride.

Japanese Patent Application Laid-Open No. 11-302198 International Publication No. 2016/052277 JP 2007-277222 A JP 2014-152172 A JP 2017-190314 A

The emulsion compositions described in Patent Documents 1 and 2 have been examined in terms of medicinal efficacy, irritation, and usability, but not in terms of stability. The present inventor focused on a formulation that combines both ufenamate and isopropylmethylphenol in an emulsion composition, and prepared an emulsion composition containing these ingredients, but encountered problems with the composition's properties becoming unstable, such as separation from the emulsion composition after storage.

The present invention aims to provide an emulsion composition containing ufenamate and isopropylmethylphenol, which has excellent emulsion stability.

The inventors of the present invention have conducted extensive research into emulsion compositions containing ufenamate and isopropylmethylphenol and have surprisingly found that excellent emulsion stability can be achieved by incorporating lidocaine and/or a salt thereof, which was previously unknown for its emulsion stabilizing effect. The present invention was completed through further research based on this knowledge.

That is, the present invention provides the following aspects.
Item 1. An emulsion composition comprising (A) ufenamate, (B) isopropylmethylphenol, and (C) lidocaine and/or a salt thereof.
Item 2. The emulsion composition according to Item 1, comprising the component (C) in a total amount of 0.1 to 5% by weight.
Item 3. The emulsion composition according to item 1 or 2, wherein the total amount of the component (C) is 0.005 to 5 parts by weight per 1 part by weight of the component (A).
Item 4. The emulsion composition according to any one of Items 1 to 3, wherein the (C) component is contained in a total amount of 0.03 to 500 parts by weight per 1 part by weight of the (B) component.
Item 5. The emulsion composition according to any one of Items 1 to 4, comprising an oil component selected from the group consisting of higher alcohols, ester oils, liquid hydrocarbon oils, and silicone oils.
Item 6. The emulsion composition according to any one of Items 1 to 5, which contains a nonionic surfactant selected from the group consisting of glycerin fatty acid esters, polyoxyethylene hydrogenated castor oil, and polyethylene glycol fatty acid esters.
Item 7. A method for emulsion stabilization, comprising blending (C) lidocaine and/or a salt thereof together with the component (A) and the component (B) in an emulsion composition containing (A) ufenamate and (B) isopropylmethylphenol.

According to the present invention, an emulsion composition containing ufenamate and isopropylmethylphenol can be provided with excellent emulsion stability.

1. Emulsion Composition The emulsion composition of the present invention is characterized by containing (A) ufenamate (hereinafter also referred to as "component (A)"), (B) isopropylmethylphenol (hereinafter also referred to as "component (B)"), and (C) lidocaine and/or a salt thereof (hereinafter also referred to as "component (C)"). The emulsion composition of the present invention will be described in detail below.

(A) Ufenamate The emulsion composition of the present invention contains ufenamate as component (A). Ufenamate is also known as butyl flufenamate, and is a known component as a poorly water-soluble non-steroidal anti-inflammatory drug.

In the emulsion composition of the present invention, the content of component (A) is appropriately set depending on the medicinal effect to be imparted, and may be, for example, 1 to 20% by weight, preferably 2 to 10% by weight, and more preferably 3 to 7% by weight.

(B) Isopropylmethylphenol The emulsion composition of the present invention contains isopropylmethylphenol as component (B). Isopropylmethylphenol is also called 3-methyl-4-isopropylphenol or cymen-5-ol, and is a component known as a poorly water-soluble bactericide.

The amount of component (B) in the emulsion composition of the present invention is not particularly limited and can be appropriately determined depending on the medicinal effect to be imparted, but examples of this include 0.01 to 3% by weight, preferably 0.02 to 2.0% by weight, more preferably 0.02 to 1.5% by weight, even more preferably 0.01 to 1% by weight, even more preferably 0.05 to 0.5% by weight, and particularly preferably 0.07 to 0.3% by weight.

(C) Lidocaine and/or a salt thereof The emulsion composition of the present invention contains lidocaine and/or a salt thereof as component (C). Lidocaine is also known as 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide, and is a known drug known to have a local anesthetic effect. Emulsion compositions containing components (A) and (B) have poor emulsion stability, but the emulsion composition of the present invention exhibits excellent emulsion stability by incorporating component (C).

There are no particular limitations on the salt of lidocaine as long as it is pharma- ceutical acceptable, but specific examples include inorganic acid salts such as hydrochloride.

In the emulsion composition of the present invention, one type of lidocaine and its salts may be selected and used alone, or two or more types may be used in combination. Among lidocaine and its salts, preferred examples include lidocaine and lidocaine hydrochloride (xylocaine), and more preferred examples include lidocaine.

The content of component (C) in the emulsion composition of the present invention is not particularly limited, but may be, for example, 0.1 to 5% by weight in terms of the total amount of lidocaine and its salts. From the viewpoint of obtaining even better emulsion stability, the content of component (C) is preferably 0.2 to 5.0% by weight, more preferably 0.5 to 5.0% by weight, 0.5 to 4.0% by weight, or 0.5 to 3.0% by weight.

In addition, since the emulsion composition of the present invention has excellent emulsion stability, even if the amount of component (C) is less than the effective amount as a local anesthetic or antipyretic/anti-inflammatory agent, it can effectively achieve emulsion stabilization effects. From this perspective, the content of component (C) in the emulsion composition of the present invention may be, for example, 0.1 to 0.4% by weight, 0.1 to 0.3% by weight, 0.1 to 0.2% by weight, or 0.2 to 0.3% by weight, in terms of the total amount of lidocaine and its salts.

In the emulsion composition of the present invention, the ratio of component (C) to component (A) is determined according to the respective contents of components (A) and (C), but from the viewpoint of obtaining even better emulsion stability, for example, the content of component (C) per part by weight of component (A) is 0.005 to 5 parts by weight, preferably 0.02 to 2 parts by weight, more preferably 0.1 to 0.7 parts by weight, 0.1 to 0.6 parts by weight, or 0.1 to 0.5 parts by weight, in terms of the total amount of lidocaine and its salts.

In the emulsion composition of the present invention, the ratio of component (C) to component (B) is determined according to the respective contents of components (B) and (C). From the viewpoint of obtaining even better emulsion stability, for example, the content of component (C) per 1 part by weight of component (B) is 0.03 to 500 parts by weight, preferably 0.1 to 200 parts by weight, more preferably 2 to 50 parts by weight, and even more preferably 5 to 30 parts by weight, or 5 to 25 parts by weight, in terms of the total amount of lidocaine and its salts.

In the emulsion composition of the present invention, the ratio of component (C) to the sum of components (A) and (B) is determined according to the above-mentioned respective contents of components (A), (B), and (C). From the viewpoint of obtaining even better emulsion stability, for example, the content of component (C) per 1 part by weight of the sum of components (A) and (B) is, for example, 0.004 to 5 parts by weight, preferably 0.01 to 2 parts by weight, more preferably 0.04 to 0.7 parts by weight, and even more preferably 0.09 to 0.6 parts by weight, or 0.09 to 0.5 parts by weight, of lidocaine and its salts.

Oil The emulsion composition of the present invention contains an oil as a base component of the oil phase. The oil is not particularly limited as long as it is pharma- ceutical or cosmetically acceptable, and examples of the oil include liquid oil, solid oil, higher alcohol, etc. These oils may be used alone or in combination of two or more.

The oil content in the emulsion composition of the present invention may be appropriately set depending on the emulsion type, form, and application of the emulsion composition, but may be, for example, 5 to 60% by weight, preferably 7 to 30% by weight, and more preferably 10 to 15% by weight.

(Liquid oil)
Liquid oils are oils that maintain a liquid form at 25° C. The liquid oils used in the present invention may be any oils that are commonly used in cosmetics, topical medicines, and the like, and examples thereof include fatty acids such as oleic acid and isostearic acid; ester oils such as cetyl ethylhexanoate, ethylhexyl palmitate, octyldodecyl myristate, neopentyl glycol diethylhexanoate, glyceryl tri-2-ethylhexanoate, octyldodecyl oleate, isopropyl myristate, glyceryl triisostearate, and glyceryl di-methylmethoxycinnamate-monoethylhexanoate; silicone oils such as dimethylpolysiloxane, methylhydrogenpolysiloxane, methylphenylpolysiloxane, and octamethylcyclotetrasiloxane; and liquid hydrocarbon oils such as liquid paraffin, squalene, and squalane.

Among these liquid oils, from the viewpoint of superior emulsion stability, preferred are ester oil, silicone oil, and liquid hydrocarbon oil, and more preferred are isopropyl myristate, dimethylpolysiloxane, and liquid paraffin.

These liquid oils may be used alone or in combination of two or more.

When liquid oil is contained in the emulsion stabilizer of the present invention, the content is not particularly limited and may be appropriately set depending on the emulsion type, form, and application of the emulsion composition, but may be, for example, 0.01 to 30% by weight, preferably 0.1 to 20% by weight, more preferably 1 to 15% by weight, and even more preferably 5 to 10% by weight.

When the emulsion stabilizer of the present invention contains an ester oil, the content is 0.2 to 3.5% by weight, preferably 0.3 to 2% by weight, and more preferably 0.5 to 1% by weight, from the viewpoint of obtaining better emulsion stability.

When silicone oil is contained in the emulsion stabilizer of the present invention, the content is 0.3 to 2% by weight, preferably 0.5 to 1.5% by weight, and more preferably 0.7 to 1% by weight, from the viewpoint of obtaining better emulsion stability.

(solid oil)
A solid oil is an oil that maintains a solid form at 25° C. The solid oil used in the present invention may be any oil that is usually used in cosmetics, topical medicines, etc., and examples thereof include solid oils such as candelilla wax, rice bran wax, beeswax, cotton wax, carnauba wax, lanolin, shellac wax, ozokerite, ceresin, polyethylene wax, microcrystalline wax, petrolatum, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, 12-hydroxystearic acid, undecylenic acid, myristyl myristate, cetyl myristate, stearyl stearate, cetyl stearate, cetyl palmitate, cholesteryl stearate, cholesteryl oleate, dextrin palmitate, inulin stearate, hydrogenated jojoba oil, ceresin wax, solid paraffin wax, polyethylene wax, and silicone wax.

These solid oils may be used alone or in combination of two or more.

When solid oil is contained in the emulsion composition of the present invention, the content is not particularly limited and may be appropriately set depending on the emulsion type, form, and application of the emulsion composition, but may be, for example, 0.1 to 50% by weight, preferably 1 to 30% by weight, and more preferably 5 to 15% by weight.

(Higher alcohol)
The higher alcohol is a monohydric alcohol having 6 or more carbon atoms in one molecule. The number of carbon atoms in one molecule of the higher alcohol used in the present invention may be 6 or more, preferably 6 to 34, and more preferably 14 to 22.

The higher alcohols used in the present invention may be any alcohol normally used in cosmetics and topical medicines, such as myristyl alcohol, cetyl alcohol (cetanol), oleyl alcohol, stearyl alcohol, isostearyl alcohol, behenyl alcohol, and lanolin alcohol.

Among these higher alcohols, cetyl alcohol (cetanol) and lanolin alcohol are preferred from the viewpoint of obtaining superior emulsion stability.

These higher alcohols may be used alone or in combination of two or more.

When the emulsion composition of the present invention contains a higher alcohol, the content is not particularly limited and may be appropriately set depending on the emulsion type, form, and application of the emulsion composition, but may be, for example, 0.1 to 50% by weight, preferably 1 to 30% by weight, more preferably 2 to 15% by weight, and even more preferably 3 to 10% by weight.

When liquid oil and higher alcohol are used in combination in the emulsion composition of the present invention, the ratio between them is not particularly limited, but for example, the content of higher alcohol per 100 parts by weight of liquid oil is 1 to 200 parts by weight, preferably 10 to 150 parts by weight, more preferably 20 to 100 parts by weight, and even more preferably 30 to 60 parts by weight.

The emulsion composition of the present invention contains water as a base component of the aqueous phase of the emulsion composition. The content of water in the emulsion composition of the present invention may be appropriately set depending on the emulsion type, form, application, etc. of the emulsion composition, and may be, for example, 30 to 95% by weight, preferably 30 to 90% by weight, more preferably 30 to 80% by weight, and even more preferably 30 to 75% by weight.

In addition, since the emulsion composition of the present invention has excellent emulsion stability that suppresses separation after storage, it is possible to obtain excellent emulsion stability even when the emulsion composition contains a large amount of water, which is inherently more likely to cause aqueous phase separation. In view of such effects of the present invention, a suitable embodiment of the emulsion composition of the present invention is an emulsion composition having a relatively high water content. More specifically, a suitable example of the water content in the emulsion composition of the present invention is 50 to 90% by weight, preferably 60 to 80% by weight, and more preferably 65 to 75% by weight.

Surfactants The surfactant is not particularly limited as long as it is pharma- ceutically or cosmetically acceptable, and examples thereof include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc. Among these surfactants, nonionic surfactants are preferred from the viewpoint of obtaining better emulsion stability.

Specific examples of nonionic surfactants include polyoxyethylene hydrogenated castor oil; sorbitan fatty acid esters (e.g., sorbitan monooleate, sorbitan monoisostearate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquioleate, sorbitan trioleate, diglycerol sorbitan penta-2-ethylhexyl acid, diglycerol sorbitan tetra-2-ethylhexyl acid, etc.); glycerin fatty acid esters (e.g., monoglyceryl cottonseed oil fatty acid, glyceryl monoerucate, glyceryl sesquioleate, glyceryl monostearate (glycerin stearate), α,α'-pioleate, glyceryl ... glyceryl monostearate, glyceryl malate, etc.); propylene glycol fatty acid esters (e.g., propylene glycol monostearate, etc.); glycerin alkyl ether; steareth-2; polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tetraoleate, etc.); polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan pentaoleate, polyoxyethylene sorbit monostearate, etc.); polyoxyethylene glycerin fatty acid esters (e.g., polyoxyethylene glycerin monostearate, polyoxyethylene glycerin monoisostearate, polyoxyethylene glycerin triisostearate, etc.); polyoxyethylene fatty acid esters (e.g., polyoxyethylene monooleate, polyoxyethylene monostearate (polyoxyl stearate), polyoxyethylene distearate, polyoxyethylene monodioleate, ethylene glycol distearate, etc.); polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene polyoxyethylene stearyl ether, polyoxyethylene behenyl ether, polyoxyethylene 2-octyldodecyl ether, polyoxyethylene cholestanol ether, etc.); Pluronic types (e.g., Pluronic, etc.); polyoxyethylene-polyoxypropylene alkyl ethers (e.g., polyoxyethylene-polyoxypropylene-cetyl ether, polyoxyethylene-polyoxypropylene-2-decyltetradecyl ether, polyoxyethylene-polyoxypropylene monobutyl ether, polyoxyethylene-polyoxypropylene hydrogenated lanolin, polyoxyethylene-polyoxypropylene glycerin ether, etc.); steareth-21, etc.

Among these nonionic surfactants, from the viewpoint of obtaining better emulsion stability, polyoxyethylene hydrogenated castor oil, glycerin polyglycerin fatty acids, and polyoxyethylene fatty acid esters are preferred, and polyoxyethylene hydrogenated castor oil, glyceryl monostearate (glycerin stearate), and polyoxyethylene monostearate (polyoxyl stearate) are more preferred.

These surfactants may be used alone or in combination of two or more.

In the emulsion composition of the present invention, the content of the surfactant may be appropriately set depending on the type of surfactant used, etc., but may be, for example, 0.5 to 7% by weight, preferably 1 to 5% by weight, more preferably 2 to 5% by weight, and even more preferably 3 to 5% by weight.

Other Components In addition to the components described above, the emulsion composition of the present invention may contain other commonly used additives as necessary. Examples of such additives include polyhydric alcohols, thickeners, pH regulators, buffers, solubilizers, chelating agents, preservatives, antioxidants, stabilizers, fragrances, colorants, etc.

The polyhydric alcohol is not particularly limited as long as it is pharma- ceutically or cosmetically acceptable, and examples thereof include dihydric alcohols such as propylene glycol, 1,3-butylene glycol (BG), ethylene glycol, isoprene glycol, diethylene glycol, and dipropylene glycol; trihydric alcohols such as glycerin, and polyethylene glycols such as Macrogol 4000 and Macrogol 6000. These polyhydric alcohols may be used alone or in combination of two or more. Among these polyhydric alcohols, from the viewpoint of obtaining better emulsion stability, dihydric alcohols and trihydric alcohols are preferred, and 1,3-butylene glycol (BG) and glycerin are more preferred. When a polyhydric alcohol is contained in the emulsion composition of the present invention, the content may be appropriately set according to the type of polyhydric alcohol used, and may be, for example, 1 to 20% by weight, preferably 5 to 15% by weight, and more preferably 7 to 13% by weight. Furthermore, when glycerin is contained in the emulsion composition of the present invention, the content is, for example, 0.5 to 10% by weight, preferably 1 to 7% by weight, and more preferably 1 to 5% by weight, from the viewpoint of obtaining better emulsion stability.

It is preferable to incorporate a thickener from the viewpoint of further improving the emulsion stabilizing effect of the emulsion stabilizer of the present invention. The thickener is not particularly limited as long as it is pharma- ceutical or cosmetically acceptable, but examples thereof include carboxyvinyl polymer, hypromellose, polyvinylpyrrolidone, sodium alginate, ethyl cellulose, sodium carboxymethylcellulose, xanthan gum, carrageenan, etc., and preferably carboxyvinyl polymer and xanthan gum. When a thickener is contained in an emulsion composition containing the emulsion stabilizer of the present invention, the content thereof may be appropriately set according to the type of thickener used, but from the viewpoint of obtaining better emulsion stability, for example, 0.1 to 2% by weight, preferably 0.1 to 1.8% by weight, more preferably 0.2 to 1.5% by weight, even more preferably 0.4 to 1% by weight, and even more preferably 0.5 to 0.8% by weight.

Furthermore, in addition to the above-mentioned components, the emulsion composition of the present invention may contain, as necessary, medicinal components capable of exerting pharmaceutical or cosmetic physiological functions. Examples of such medicinal components include steroids (dexamethasone, dexamethasone hydrochloride, dexamethasone acetate, hydrocortisone hydrochloride, prednisolone valerate, prednisolone acetate, etc.), antihistamines (diphenhydramine, diphenhydramine hydrochloride, chlorpheniramine maleate, etc.), local anesthetics (lidocaine, dibucaine, procaine, tetracaine, bupivacaine, mepivacaine, chloroprocaine, proparacaine, meprylcaine, or salts thereof), alkyl benzoates (e.g., ethyl aminobenzoate, diethylaminoethyl p-butylaminobenzoate hydrochloride), orthocaine, oxethazaine, oxypolyethyleneoxydecane, scolymus extract, percaminepase, tesit decitin, etc.), anti-inflammatory agents (arabic acid, benzoic ... anthoin, salicylic acid, glycol salicylate, methyl salicylate, indomethacin, felbinac, diclofenac sodium, loxoprofen sodium, etc.), bactericides (benzalkonium chloride, dequalinium chloride, benzethonium chloride, cetylpyridinium chloride, chlorhexidine hydrochloride, chlorhexidine gluconate, aqueous ammonia, sulfadiazine, lactic acid, phenol, etc.), antipruritic agents (crotamiton, thianthol, etc.), skin protectants (collodion, castor oil, etc.), blood circulation promoting components (vanillylamide nonylate, benzyl nicotinate, capsaicin, capsicum extract, etc.), vitamins (vitamins A, B, C, D, E, etc.), mucopolysaccharides (sodium chondroitin sulfate, glucosamine, hyaluronic acid, etc.), etc. These medicinal components may be used alone or in combination of two or more. Furthermore, when these medicinal ingredients are contained in the emulsion composition containing the emulsion stabilizer of the present invention, the content of the ingredients may be appropriately set depending on the type of medicinal ingredient used, the desired effect, etc.

Formulation and Use The emulsion type of the present invention may be either water-in-oil type or oil-in-water type. The emulsion composition of the present invention has excellent emulsion stability that suppresses separation after storage, so that even if it contains a lot of water, such as oil-in-water type, which is inherently more prone to aqueous phase separation, it can have excellent emulsion stability. In view of the effects of the present invention, the preferred emulsion type of the emulsion composition of the present invention is oil-in-water type, which has a relatively high water content.

The emulsion composition of the present invention can be used as an external preparation such as a cosmetic, an external quasi-drug, or an external medicine. The product form of the emulsion composition of the present invention is not particularly limited, and examples thereof include creams, ointments, emulsions, gels, oils, lotions, liniments, and aerosols. Of these, creams, ointments, emulsions, and lotions are preferred, and creams, emulsions, and lotions are more preferred.

The emulsion composition of the present invention can be manufactured according to the formulation method of known emulsion preparations depending on the emulsion type.For example, the method of manufacturing the emulsion composition of the present invention includes a method of dividing the components to be contained into water-soluble components and oily components, preparing an aqueous phase containing the water-soluble components and an oily phase containing the oily components, and emulsifying them according to a known method.

2. Emulsion stabilization method As described above, lidocaine and/or a salt thereof exhibits excellent emulsion stability in an emulsion composition containing ufenamate and isopropylmethylphenol. Therefore, the present invention further provides a method for emulsion stabilization, which comprises blending (C) lidocaine and/or a salt thereof together with the component (A) and the component (B) in an emulsion composition containing ufenamate (A) and isopropylmethylphenol (B).

In the emulsion stabilization method of the present invention, emulsion stabilization refers to suppressing separation of the emulsion composition after storage. Separation refers to separation of the aqueous phase and/or oil phase from the emulsion composition. A more preferred aspect of emulsion stabilization is suppressing separation of the aqueous phase from the emulsion composition after storage, and a more preferred aspect is maintaining the emulsion state of the emulsion composition uniform after storage, that is, maintaining a state in which the droplets in the emulsion are uniformly dispersed in the dispersion medium.

In the emulsion stabilization method of the present invention, the type and content of each component used, the type and content of components blended in the emulsion composition, and the formulation form are the same as those in "1. Emulsion composition" above.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these.

Test Example The emulsion compositions shown in Table 1 were prepared. Specifically, each component (I) shown in Table 1 was heated and mixed at 65 to 75°C to dissolve the solids, and further components (A) to (C) were mixed and dissolved to obtain an oil phase. To this was added an aqueous phase obtained by heating and mixing each component (II) shown in Table 1 at 65 to 75°C to dissolve the solids, emulsifying the mixture using a homomixer, and cooling and stirring to 35°C to produce a creamy oil-in-water emulsion composition.

10 g of each of the obtained emulsion compositions was filled into a glass bottle (screw tube bottle No. 4, capacity 13.5 mL, manufactured by Maruemu Co., Ltd., transparent), sealed, and stored at 60° C. for 3 weeks. After storage, each emulsion composition was visually observed, and the emulsion stability was evaluated based on the following criteria. The results are shown in Table 1.
×: Separation of the aqueous phase was clearly observed.
Δ: Some separation of the aqueous phase was observed.
◯: Creaming tendency is observed, but no separation is observed.
◎: The emulsion is uniform and no separation is observed.
The creaming tendency refers to a non-uniform emulsified state, specifically, a state in which droplets in the generated emulsion are in the process of floating up or sinking down due to the difference in specific gravity with the dispersion medium.

As is clear from Table 1, the emulsion composition containing ufenamate and lidocaine (Comparative Example 1) showed separation of the aqueous phase after storage, and thus the emulsion state was significantly unstable. In contrast, it was found that when lidocaine was further added to the emulsion composition containing ufenamate and lidocaine (Examples 1 to 4), excellent emulsion stability was obtained. This effect of improving emulsion stability was particularly notable in Examples 2 to 4. In addition, the emulsion composition prepared in the same manner as Comparative Example 1 except that it did not contain isopropylmethylphenol, and the emulsion composition prepared in the same manner as Comparative Example 1 except that it did not contain ufenamate, both showed separation of the aqueous phase and were emulsion states that were unstable, but the degree of this was not as significant as in Comparative Example 1.

Formulation Examples Emulsion compositions having the formulations shown in Table 2 were prepared in the same manner as in the above-mentioned Test Examples. All of the emulsion compositions had excellent emulsion stability.

Claims (7)

An emulsion composition (excluding those containing diphenhydramine and/or a salt thereof), comprising (A) ufenamate, (B) isopropylmethylphenol , ( C) lidocaine and/or a salt thereof , and a nonionic surfactant . The emulsion composition according to claim 1, containing 0.1 to 5% by weight of the component (C) in total. The emulsion composition according to claim 1 or 2, wherein the total amount of the (C) component is 0.005 to 5 parts by weight per 1 part by weight of the (A) component. The emulsion composition according to any one of claims 1 to 3, wherein the total amount of the (C) component is 0.03 to 500 parts by weight per 1 part by weight of the (B) component. The emulsion composition according to any one of claims 1 to 4, which contains an oil selected from the group consisting of higher alcohols, ester oils, liquid hydrocarbon oils, and silicone oils. The emulsion composition according to any one of claims 1 to 5 , wherein the nonionic surfactant is selected from the group consisting of glycerin fatty acid esters, polyoxyethylene hydrogenated castor oil, and polyethylene glycol fatty acid esters. A method for emulsion stabilization , comprising blending (C) lidocaine and/or a salt thereof together with the (A) component , the (B) component, and the nonionic surfactant into an emulsion composition (excluding those containing diphenhydramine and/or a salt thereof) containing (A) ufenamate, (B) isopropylmethylphenol, and a nonionic surfactant .