Antimicrobial Compositions Employing Certain Betaines and Certain Amine Oxides

The present invention relates to antimicrobial composition of enhanced efficacy and safety. More particularly, the invention relates to antimicrobial compositions having low toxicity and broad spectrum antimicrobial activity comprising certain amphoteric surfactants which per se have limited antimicrobial use. Still more particularly, the invention is concerned with antimicrobial compositions of enhanced gram positive and gram negative activity comprising in admixture:

(a) an acyl-N-betaine (0.1 - 40.0 parts, by weight),

(b) an alkyl-N,N-dimethylamine oxide or an acylamido t-amine oxide (0.1 - 40.0 parts, by weight), and

(c) a protonating agent, such as hydrochloric acid, acetic acid or citric acid in an amount sufficient to adjust the pH of the overall composition to about 5.5, or below.

The composition of the present invention exhibits sustained periods of antimicrobial activity, particularly in the control of body odor.

As is known, an outstanding method for the control of body odor is to thoroughly wash the body with soap, but so prolific are the microbial flora of the skin that distinctive malodors tend to return within several hours after washing. To provide long periods of protection, compositions have been developed that contain either an (a) astringent, such as aluminum chlorohydrate, which inhibit apocrine and eccrine gland secretions or (b) an antimicrobial agent, such as hexachlorophene or trichlorocarbanilamide. Unfortunately, the former astringent compositions have limited value, since they have little or no control of microbial decomposition of debris and uncontrolled secretions and where there is control of secretions, such use suffers from severe shortened time periods to obtain effective control. Nonetheless, the latter antimicrobial compositions have enjoyed widespread use. However, there have been recent investigations into topical and systemic toxicity of the named germicides used to control body odor. These investigations have led to severe restrictions, for instance, on the utilization of hexachlorophene and the recognition of the dangers of other germicides. Further, the use of astringents have only limited utility usually due to its harsh action on skin, particularly, on those who have sensitive skin. If a safe antimicrobial composition of low toxicity could be provided which would inhibit the the development of body odor for relatively long periods of time, eg., at least twenty-four (24) hours, or longer, such a composition would satisfy a real need in the art.

It is a principal object of the invention to provide an antimicrobial composition of enhanced efficacy and safety which possesses broad spectrum activity in combating body odor and topical infections. It is a further object of the invention to provide an antimicrobial composition comprising at least an acyl-N-betaine surfactant and an alkyl-N,N-dimethylamine oxide, an alkyl-N,N-dihydroxyethylamine oxide, or an acylamido t-amine oxide adjusted to a pH of 5.5, or below, so as to control gram positive bacteria, gram negative bacteria, fungi, and yeast, when topically applied. Other objects and advantages will become apparent from a consideration of the ensuing description.

According to the invention, there are provided antimicrobial compositions consisting essentially of a mixture of (a) an acyl-N-betaine, and (b) an alkyl-N,N-dimethylamine oxide, an alkyl-N,N-dihydroxyethylamine oxide, or an acylamido t-amine oxide. The components are admixed at a temperature ranging from about 25.degree. C to 80.degree. C in a substantially aqueous or non-aqueous environment and adjusted to a pH of 5.5, or below, to provide a substantially uniform homogeneous composition having both enhanced broad spectrum activity and low toxicity.

In general, the acyl-N-betaine surfactant employed as a zwitterion component of the composition can be written as: ##STR1## where R is a higher alkyl having from 10 to 18 carbon atoms. Illustrative of such acyl-N-betaine are cocoamido-N-betaine, cetylamido-N-betaine, stearylamido-N-betaine, isostearylamido-N-betaine, oleylamido-N-betaine, or mixtures of the same.

The (1) alkyl-N,N-dimethylamine oxide, (2) alkyl-N,N-dihydorxyethylamine oxide, or (3) acylamido t-amine oxide component of the aforementioned mixture, has the respective structure: ##STR2## where R.sub.1 is a higher alkyl from 10 to 18 carbon atoms, as for instance, radicals such as decyl, undecyl, lauryl, tridecyl, myristyl, cetyl, stearyl, isostearyl, oleyl or mixtures of the same. Exemplary of the latter amine oxides are decyl-N,N-dimethylamine oxide, lauryl-N,N-dimethylamine oxide, stearyl-N,N-dimethylamine oxide, oleyl-N,N-dimethylamine oxide, cocoamidotrimethylene-N,N-dimethylamine oxide, stearylamidotrimethylene-N,N-dimethylamine oxide, decyl-N,N-dihydroxyethylamine oxide, lauryl-N,N-dihydroxyethylamine oxide, coco-N,N-dihydroxyethylamine oxide, stearyl-N,N-dihydroxyethylamine oxide, oleyl-N,N-dihydroxyethylamine oxide, and mixtures of the same.

In general, the protonating agent necessary to supply the required pH to the overall composition is, for instance, any inert organic or inorganic acid, such as hydrochloric acid, phosphoric acid, sulfuric acid, citric acid, acetic acid, nicotinic acid, and the like. A good operating pH range for the overall composition is 4.0 to 5.5 and, preferably, from about 4.7 to 5.2. The pH of an aqueous solution comprising the above enumerated components of the invention is determined by employing 0.5%, by weight, of active components at a glass electrode to precisely define the acidity of the composition.

In practice, each of the components of the overall composition ranges widely from 0.1 part to 40.0 parts and the balance an inert solvent, such as water or a lower monohydric aliphatic alcohol for a total of at least 100 parts. Where water is employed, small amounts of lower alkyl alcohols may also be added thereto to provide ease in formulation. The pH of the total composition is then adjusted to the requisite pH by adding a suitable inorganic or organic acid thereto. The composition can be employed as a solution or as a spray, such as an aerosol spray utilizing commercially available "Freon" fluorocarbon or equivalent propellant.

Advantageously, the compositions of the present invention possess an extremely low toxicity exhibiting as an LD.sub.50 in Swiss-Webster mice greater than 4 grams per kilogram by intraperitoneal or oral administration. Further, there are observed a lack of primary irritation to the skin and less eye irritation as compared with ordinary soap.

It has been found that the aforementioned compositions can be advantageously employed as a general personal body wash. Body odor in the axillary and anal/genital areas in particular will be inhibited for periods in excess of 24 hours and usually, will exhibit inhibition from 72 to 96 hours.

In order to facilitate a further understanding of the invention, the following examples are presented primarily for purposes of illustrating certain more specific details thereof. The invention is not to be deemed as limited thereby except as defined in the claims. Unless otherwise noted, all parts and percentages are by weight.

In this example, several compositions are prepared and used as a body wash. Twelve panels each consisting of five men and five women as subjects are selected and supplied with samples of the compositions herein defined in Table I below. After 24 hours have elapsed since the panel members' last washing, each is instructed to wash, noting particularly the axillary odor before and after washing. The panel members are then examined during the next 24 hours and longer for the time span when typical body odors develop. These times are then noted and recorded in Table I below.

From the above table, it can be clearly seen that the compositions of the present invention at the adjusted pH range cause a marked improvement in body odor inhibition.

The relation between antimicrobial activity and control of body odor is determined by subjecting each of the panel members of Example 1 to additional washing tests employing the compositions of Example 1. There are obtained the density of microbes in the axillary area of each panelist by using a Rodac plate comprising Tryptose soy agar with Tween.sup..RTM. 80 and lecithin to neutralize residual germicide. The panelist presses the plate for 30 seconds to the axillary area of the armpit. The plates are then incubated at 37.degree. C for 24 hours and the number of colonies are counted. The density in the colonies per square inch is next calculated. The date obtained are noted in the table below and are the average values of the subjects treated.

There are admixed at 40.degree. C stearylamido-N-betaine (6.25 gm.), coco-N,N-dimethylamine oxide (13 gm.) citric acid (4.5 gm.) and 125 gm. of distilled water. The pH of the mixture when diluted to 0.5% actives is equal to 5.0.

The mixture is tested as a body shampoo and after 60 hours subsequent to washing, the panel reported no evidence of body ordor in the axillary areas.

A mixture of stearylamido-N-betaine (6.5 gms.), coco-N,N-dimethylamine oxide (13 gms.), acetic acid (4.5 gms.), and 66 gms. of water, formed at 50.degree. l C and having a pH on dilution is equal to 5.1, is employed as a body wash as in Example 3 above. Body odor is absent after 72 hours.

Substituting hydrochloric acid for acetic acid in the above mixture, a similar result is noted.

There are admixed cetylamido-N-betaine (2.5 gms.), myristyl-N,N-dimethylamine oxide (5.5 gms.), citric acid (2.0 gms.) and 87 gms. of water. The mixture is heated to 60.degree. C and the pH determined on dilution is 5.5

As in Example 4 above, the mixture is used as a body wash to determine axillary and pubic body odors. After 72 hours subsequent to washing, no body odor is detected.

A mixture of laurylamido-N-betaine (5.2 gms.), 70/30 myristyl/palmitic-N,N-dimethylamine oxide mixture (5.5 gms.) citric acid (0.7 gms.) and water (108 gms.) is heated to 35.degree. C. The pH of the diluted solution is 5.4 and is used as a body wash. No body odor is detected for 72 hours after washing.

There are added at 30.degree. C. 6.2 gms. of cocoamido-N-betaine, 6.2 gms. of 70/30 myristyl/palmitic-N,N-dimethylamine oxide, 5. gms. of isopropanol, 0.7 gm. of citric acid, and 92 gms. of water. Upon dilution, the pH measured equals 5.5.

The mixture controls body odor for 48 hours after washing in all panel members.

There are admixed at 75.degree. C. 10 gms. of cetylamido-N-betaine, 10 gms. of cocoamido-betaine, 42 gms. of 70/30 myristyl/palmitic-N,N-dimethylamine oxide, 15 gms. of isopropanol, 9 gms. of citric acid, and 550 gms. of water. There is obtained a solution having a pH=5.0 on dilution and the preparation when used as a body wash controls odor for more than 72 hours after washing.

This example illustrates the formulation of a solid composition comprising of 32 gms. of stearylamido-N-betaine, 32 gms. of myristyl/palmitic-N, N-dimethylamine oxide, 20 gms. of isopropanol, 40 gms. of water and 6.3 gms. of citric acid. The mixture is vigorously stirred and heated to a temperature of 80.degree. C. Resultant composition is then dried by evaporation and cooled. There is recovered 110 gms. of a waxy solid product having a pH equal to 5.0 at a 0.5% aqueous concentration.

The solid composition is employed for washing and controlling body odor for 48 hours after washing.

In this example there is prepared a spray composition. There are admixed 0.1 gm. cetylamido-N-betaine, 0.1 gm. coco-N,N-dimethylamine oxide, 10 gms. isopropanol, and 0.02 gm. of citric acid. The mixture is heated to 40.degree. C, cooled, and admixed with 100 gms. of liquified butane in a suitable container.

Resultant composition is sprayed under the armpits of several panelists. Each reports underarm odor control for at least 48 hours after use.

There are added to a suitable mixing vessel with stirring 8 gms. of cocoamido-N-betaine, 8 gms. of stearylamido-N-betaine, 16 gms. of 70/30 myristyl/palmitic-N,N-dimethylamine oxide, 3.3 gms. of citric acid and q.s. to 250 gms. of water. Resultant mixture is stirred vigorously and heated to 60.degree. C for fifteen minutes.

Upon cooling, the pH of the mixture is found to possess a pH equal to 4.7 on dilution.

Resultant composition is employed as a body wash following the procedure of Example 2 above. After 12 hours, it is found by each of the panelists that no body odor is detected.