JP7465066B2 - Emulsion stabilizer - Google Patents

Description

The present invention relates to the use of lidocaine to stabilize the properties of an emulsion composition.

Emulsion compositions can be blended with aqueous and oily components, 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. However, emulsion compositions are prone to separation when stored for long periods of time, and have drawbacks in terms of emulsion stability.

As a method for improving emulsion stability, a method of increasing the viscosity of the emulsion composition is used. However, to produce an emulsion composition with a high viscosity, it is necessary to blend a specific amount or more of higher alcohol or to blend a large amount of thickener. Furthermore, there is a limit to the emulsion stabilization that can be achieved by simply increasing viscosity, and it cannot be said that the emulsion stability is still satisfactory. Furthermore, blending a large amount of thickener causes the emulsion composition to become sticky, resulting in a decrease in the feeling of use.

In this regard, Patent Document 1 describes a method for producing a high-viscosity emulsion composition without the need to incorporate a specific amount or more of higher alcohol or a large amount of thickener, in which an oil phase containing a nonionic surfactant, a linear higher alcohol having 16 or more carbon atoms, and an oil component and an aqueous phase containing water are emulsified at a temperature of 70°C or higher to prepare an O/W emulsion, the O/W emulsion is cooled with stirring, and stirring is stopped at a temperature above the peak temperature in the temperature range where the oil phase forms an α-gel in the aqueous phase and below 70°C, thereby obtaining a high-viscosity O/W cream with excellent emulsion stability. However, this method has drawbacks in terms of ease of production, as the operations after the emulsification process are complicated.

Given this background of conventional technology, there was a need to develop a formulation technology that provides excellent emulsion stability using a simple method.

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 2 describes an anti-inflammatory pharmaceutical composition containing tranexamic acid or its salt and a local anesthetic, and describes the use of lidocaine as the local anesthetic. Patent Document 3 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 4 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.

JP 2011-72310 A JP 2007-277222 A JP 2014-152172 A JP 2017-190314 A

The object of the present invention is to provide an emulsion composition having excellent emulsion stability.

The inventors of the present invention conducted extensive research and surprisingly found that the emulsion stability of an emulsion composition can be improved by incorporating lidocaine and/or a salt thereof, which was not previously known to have an emulsion stabilizing effect, into the emulsion composition. The present invention was completed through further research based on this finding.

That is, the present invention provides the following aspects.
Item 1. An emulsion stabilizer for an emulsion composition, comprising lidocaine and/or a salt thereof.
Item 2. The emulsion stabilizer for an emulsion composition according to Item 1, wherein the emulsion composition contains an oil component selected from the group consisting of higher alcohols, ester oils, liquid hydrocarbon oils, and silicone oils.
Item 3. The emulsion stabilizer for an emulsion composition according to Item 1 or 2, wherein the emulsion composition 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 4. The emulsion stabilizer for an emulsion composition according to any one of Items 1 to 3, wherein the lidocaine and/or a salt thereof is used in an amount of 0.1 to 5.0% by weight in total in the emulsion composition.
Item 5. A method for stabilizing an emulsion, comprising blending lidocaine and/or a salt thereof into an emulsion composition.

According to the present invention, it is possible to provide an emulsion composition with excellent emulsion stability.

1. Emulsion stabilizer The emulsion stabilizer of the emulsion composition of the present invention is characterized by containing lidocaine and/or a salt thereof. The emulsion stabilizer of the present invention will be described in detail below.

The emulsion stabilizer of the present invention contains lidocaine and /or a salt thereof as a component having an emulsion stabilizing effect. Lidocaine, also known as 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide, is a known drug known to have a local anesthetic effect or an antipyretic and anti-inflammatory effect.

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 stabilizer of the present invention, the active ingredient may be one selected from lidocaine and its salts and used alone, or two or more may be used in combination. Among lidocaine and its salts, from the viewpoint of obtaining a preferable emulsion stabilizing effect, lidocaine and lidocaine hydrochloride (xylocaine) are preferred, and lidocaine is even more preferred.

The amount of the emulsion stabilizer of the present invention to be blended in the emulsion composition is not particularly limited, but may be, for example, 0.1 to 5.0% by weight of the total amount of lidocaine and its salts in the emulsion composition. From the viewpoint of obtaining a more preferable emulsion stabilization effect, the amount of the emulsion stabilizer of the present invention to be blended in the emulsion composition 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 of the total amount of lidocaine and its salts.

In addition, since the emulsion stabilizer of the present invention has excellent emulsion stability, even if the amount of lidocaine and/or its salt is less than the effective amount as a local anesthetic or antipyretic/anti-inflammatory agent, an effective emulsion stabilizing effect can be obtained. From this viewpoint, the amount of the emulsion stabilizer of the present invention blended in the emulsion composition 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 of the total amount of lidocaine and its salt.

Emulsion Composition The emulsion composition in which the emulsion stabilizer of the present invention is blended is not particularly limited as long as it contains oil, water, and a surfactant.

(Oil content)
The oil is used as a base component of the oil phase of the emulsion composition. The oil is not particularly limited as long as it is pharma- ceutically or cosmetically acceptable, and examples thereof 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 containing the emulsion stabilizer 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 oil is an oil that maintains a liquid form at 25° C. The liquid oil used in the emulsion composition containing the emulsion stabilizer of the present invention may be any oil that is 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.

Of these liquid oils, from the viewpoint of obtaining a more favorable emulsion stabilizing effect by the emulsion stabilizer of the present invention, preferred are ester oils, silicone oils, and liquid hydrocarbon oils, 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 composition containing 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.

Solid Oil A solid oil is an oil that maintains a solid form at 25° C. The solid oil used in the emulsion composition containing the emulsion stabilizer of the present invention may be any solid oil that is usually used in cosmetics, topical medicines, etc., and examples thereof include 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 containing 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, 0.1 to 50% by weight, preferably 1 to 30% by weight, and more preferably 5 to 15% by weight.

Higher alcohols are monohydric alcohols having 6 or more carbon atoms in one molecule. The number of carbon atoms in one molecule of the higher alcohol used in the emulsion composition containing the emulsion stabilizer of the present invention may be 6 or more, preferably 6 to 34, and more preferably 14 to 22.

The higher alcohol used in the emulsion composition containing the emulsion stabilizer of 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 a more favorable emulsion stabilizing effect by the emulsion stabilizer of the present invention.

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

When a higher alcohol is contained in the emulsion composition containing 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 use 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 an emulsion composition containing the emulsion stabilizer of the present invention, the ratio between them is not particularly limited, but for example, 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 of higher alcohol per 100 parts by weight of liquid oil.

(water)
Water is contained as a base component of the aqueous phase of the emulsion composition. The content of water in the emulsion composition containing the emulsion stabilizer 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 stabilizer of the present invention has excellent emulsion stability that suppresses separation after storage, it is possible to provide excellent emulsion stability even in cases where a large amount of water is contained, in which aqueous phase separation is inherently more likely to occur. In view of such effects of the present invention, a suitable embodiment of an emulsion composition containing the emulsion stabilizer of the present invention is an emulsion composition having a relatively high water content. More specifically, a suitable example of the water content in an emulsion composition containing the emulsion stabilizer of the present invention is 50 to 90% by weight, preferably 60 to 80% by weight, and more preferably 65 to 75% by weight.

(Surfactant)
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 a more favorable emulsion stabilizing effect by the emulsion stabilizer of the present invention.

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 further improving the emulsion stabilizing effect of the emulsion stabilizer of the present invention, 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 containing the emulsion stabilizer of the present invention, the content of the surfactant may be appropriately set depending on the type of surfactant used, and 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 ingredients)
The emulsion composition containing the emulsion stabilizer of the present invention may contain, in addition to the above-mentioned components, other commonly used additives as necessary, such as 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 further improving 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 containing the emulsion stabilizer of the present invention, the content of the polyhydric alcohol 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.

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, and may be, for example, 0.1 to 2% by weight, preferably 0.1 to 0.6% by weight, and more preferably 0.2 to 0.6% by weight.

Furthermore, the emulsion composition containing the emulsion stabilizer of the present invention may contain, in addition to the above-mentioned components, medicinal ingredients capable of exerting pharmaceutical or cosmetic physiological functions, as necessary. Examples of such medicinal ingredients 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, Scopolia extract, percaminepase, tesitdesitin, etc.), and anti-inflammatory agents (ufenamate, allantoin). , salicylic acid, glycol salicylate, methyl salicylate, indomethacin, felbinac, diclofenac sodium, loxoprofen sodium, etc.), bactericides (benzalkonium chloride, dequalinium chloride, benzethonium chloride, cetylpyridinium chloride, isopropylmethylphenol, 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, chili pepper 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 emulsion composition containing the emulsion stabilizer of the present invention may be either water-in-oil type or oil-in-water type. The emulsion stabilizer of the present invention can provide excellent emulsion stability that suppresses separation even after high-temperature storage, so that even if the emulsion composition containing the emulsion stabilizer of the present invention contains a large amount of water, such as the 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 containing the emulsion stabilizer of the present invention is the oil-in-water type, which contains a relatively large amount of water.

The emulsion composition containing the emulsion stabilizer of the present invention can be used as an external preparation such as a cosmetic, topical quasi-drug, or topical medicine. The product form of the emulsion composition containing the emulsion stabilizer of the present invention is not particularly limited, but 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.

(Production method)
The emulsion composition containing the emulsion stabilizer 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 containing the emulsion stabilizer 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.

As described above, lidocaine and/or a salt thereof exert excellent emulsion stability in an emulsion composition. Therefore, the present invention further provides a method for emulsion stabilization, which comprises blending lidocaine and/or a salt thereof in an emulsion composition.

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 lidocaine and/or its salt used, the type and content of ingredients blended in the emulsion composition, and the formulation form are the same as those described above in "1. Emulsion stabilizer."

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 An emulsion composition was prepared having the composition shown in Table 1. Specifically, an oil phase was obtained by heating and mixing each component (I) shown in Table 1 at 65 to 75°C to dissolve the solids, and an aqueous phase was obtained by heating and mixing each component (II) shown in Table 1 at 65 to 75°C to dissolve the solids. The mixture was emulsified using a homomixer, and cooled to 35°C with stirring 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 not containing lidocaine (Comparative Example 1) showed significant instability in the emulsion state, as the aqueous phase separated after storage. In contrast, it was found that excellent emulsion stability was obtained when lidocaine was added to the emulsion composition (Examples 1 to 4). This improvement in emulsion stability was particularly noticeable in Examples 2 to 4.

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 (2)

An emulsion stabilizer for an emulsion composition (excluding those containing ufenamate, those containing an antihistamine and/or vegetable oil, and those containing prednisolone valerate acetate), which contains lidocaine and/or a salt thereof,
The emulsion composition contains a liquid oil, a higher alcohol, a surfactant, a polyhydric alcohol, and a thickener,
The liquid oil contains isopropyl myristate, dimethylpolysiloxane, and liquid paraffin, and the content of the liquid oil is 5 to 10% by weight;
The higher alcohols include cetyl alcohol (cetanol) and lanolin alcohol, and the content of the higher alcohols is 3 to 10% by weight;
The surfactant comprises polyoxyethylene hydrogenated castor oil, glyceryl monostearate (glycerin stearate), and polyoxyethylene monostearate (polyoxyl stearate), and the content of the surfactant is 1 to 5% by weight;
The polyhydric alcohol includes glycerin and 1,3-butylene glycol, and the content of the polyhydric alcohol is 7 to 13% by weight;
The thickener comprises xanthan gum and a carboxyvinyl polymer, and the content of the thickener is 0.2 to 0.6% by weight;
An emulsion stabilizer for an emulsion composition, wherein the lidocaine and/or a salt thereof is used in an amount of 0.1 to 5.0% by weight in total in the emulsion composition . A method for emulsion stabilization, comprising blending lidocaine and/or a salt thereof in a total amount of 0.1 to 5.0% by weight into an emulsion composition (excluding those containing ufenamate, those containing an antihistamine and/or a vegetable oil, and those containing prednisolone valerate acetate) containing 5 to 10% by weight of a liquid oil containing isopropyl myristate, dimethylpolysiloxane, and liquid paraffin, 3 to 10% by weight of a higher alcohol containing cetyl alcohol (cetanol) and lanolin alcohol, 1 to 5% by weight of a surfactant containing polyoxyethylene hydrogenated castor oil, glyceryl monostearate (glycerin stearate), and polyoxyethylene monostearate (polyoxyl stearate), 7 to 13% by weight of a polyhydric alcohol containing glycerin and 1,3-butylene glycol, and 0.2 to 0.6% by weight of a thickener containing xanthan gum and a carboxyvinyl polymer.