Abstract:
What is described is a light stable, whitish antimicrobial product which is a silver-allantoin complex encapsulated with allantoin. The molar ratio of silver-to-allantoin in the product is between 1:100 and 1:4.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to silver-allantoin complexes, and, more particularly, to a silver-allantoin complex encapsulated with allantoin. 
     2. Description of the Prior Art 
     Silver-allantoin complexes are known in the art. For example, a dark gray-to-black silver-allantoin complex having a molar ratio of silver-to-allantoin of 1:1 was described by C. Schaffer in U.S. Pat. No. 2,336,131 (1943). However, the complex was not light stable and so was of little practical use for treating antibacterial infections. 
     Accordingly, it is an object of this invention to provide a new and improved antimicrobial silver-allantoin product which is light stable and has antimicrobial activity down to 15 ppm of silver. 
     Another object of the invention is to provide an antimicrobial product which is a silver-allantoin complex encapsulated by allantoin and which is whitish in appearance, light stable and active against both gram-positive and gram-negtive bacteria, molds and yeast. 
     SUMMARY OF THE INVENTION 
     What is described herein is a light stable, whitish antimicrobial product which is a silver-allantoin complex encapsulated with allantoin, the molar ratio of silver-to-allantoin in said product being between 1:100 and 1:4, preferably 1:25 to 1:6. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The product of the invention exhibits antimicrobial activity against both gram-positive and gram-negative bacteria, molds and yeast in a standard emulsion test down to 15 ppm of silver. 
     The product of the invention is made by a defined process which comprises (a) forming an aqueous suspension of allantoin in a base, (b) adding a water soluble silver salt thereto to form a silver-allantoin complex, and (c) adding an additional amount of allantoin to encapsulate the complex with a layer of allantoin. The product then may be obtained as a purified powder by diluting with water, filtering, washing the wet cake precipitate with water, breaking up the wet cake, drying in a vacuum oven at 100° C. for about 4 hours, and grinding. The product is a fine, white powder obtained in at least a 97% yield. 
     The invention will now be described further with reference to the following examples, in which Examples 1-2 describe the process of making the product of the invention, Example 3 is evidence of the light stability of such products, and Examples 4-5 describe its antimicrobial activity. 
     EXAMPLE 1 
     To 25 g of allantoin in a 500 ml, 3-neck round bottom flask was added 75 ml water and the suspension was chilled to about 10° C. While stirring, 5.0 g of a 50% NaOH solution was added over a period of 15 minutes while maintaining the temperature at 10° C. Then a AgNO 3  solution (10.7 g AgNO 3  in 50 ml water) was added to the stirred suspension and the mixture was stirred for 15 minutes. Then an additional 75.0 g of allantoin was added. The mixture was diluted with 100 ml water, stirred for 15-30 minutes, filtered and the wet cake precipitated, and washed with water. The wet cake was broken up and dried in a vacuum oven at 100° C. for 4 hours. The dried product was ground to provide a fine, white powder (103.4 g, 96.9% yield) of a 10% silver-allantoinate complex in allantoin. The product had a silver:allantoin ratio of 1:15.7 (6.3% silver). 
     EXAMPLE 2 
     The process of Example 1 was repeated using 60 g of allantoin, 100 ml water, 15.2 g of a 50% NaOH solution, an AgNO 3  solution (32.2 g AgNO 3  in 50 ml water), an additional 40.0 g allantoin, and dilution with 50 ml water. The product was a fine, white powder (112.6 g, 93.6% yield) 30% silver-allantoinate complex in allantoin. The silver:allantoin ratio was 1:5.9 (17.1% silver). 
     EXAMPLE 3 
     The powders of Examples 1 and 2 were exposed to direct sunlight for 30 days without any change in its whitish appearance. 
     EXAMPLE 4 
     Preservative Efficacy Tests 
     Formulation: Emulsion SE1* 
     Use Level: 250 ppm (0.025%) of Silver-Allantoinate-Allantoin Product of Example 1 
     Active Level: 15 ppm of Silver 
     
                       TABLE 1______________________________________InoculumOrganism         0 Hour   21 Day______________________________________A. niger 16404    45000    50000B. cepacia 25416  42000    10000C. albicans 10231             800000  1000000E. coli 8739     1500000  1600000P. aeruginosa 9027            2000000  3100000S. aureus 6538   1500000   240000______________________________________Organism     48 hr  7 days  14 days                             21 days                                    28 days______________________________________A. niger 16404        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10B. cepacia 25416        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10C. albicans 10231        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10E. coli 8739 60     &lt;10     &lt;10   &lt;10    &lt;10P. aeruginosa 9027        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10S. aureus 6538        50     &lt;10     &lt;10   &lt;10    &lt;10______________________________________ 
    
     EXAMPLE 5 
     Use Level: 500 ppm (0.05%) of Silver-Allantoinate-Allantoin Product of Example 1 
     Active Level: 30 ppm of Silver 
     
         ______________________________________InoculumOrganism         0 Hour   21 Day______________________________________A. niger 16404    45000    50000B. cepacia 25416  42000    10000C. albicans 10231             800000  1000000E. coli 8739     1500000  1600000P. aeruginosa 9027            2000000  3100000S. aureus 6538   1500000   240000______________________________________Organism     48 hr  7 days  14 days                             21 days                                    28 days______________________________________A. niger 16404        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10B. cepacia 25416        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10C. albicans 10231        90     &lt;10     &lt;10   &lt;10    &lt;10E. coli 8739 10     &lt;10     &lt;10   &lt;10    &lt;10P. aeruginosa 9027        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10S. aureus 6538        &lt;10    &lt;10     &lt;10   &lt;10    &lt;10______________________________________ *Emulsion SE1 
    
     
         ______________________________________              Wt. %______________________________________Phase AStearic Acid         5.0Mineral Oil          2.5Cetyl Alcohol        1.0Lareth-5 and Ceteth-5 and                0.5Oleth-5 and Steareth-5Glycerol Monostearate and                1.5polyoxyethylene StearatePhase BDeionized Water      88.0Triethanolamine 99%  1.0Citric Acid 30% aqueous solution                0.6Preservative         qs______________________________________ 
    
     While the invention has been described with particular reference to certain embodiments thereof, it will be understood that changes and modifications may be made which are within the skill of the art. Accordingly, it is intended to be bound only by the following claims, in which: