Abstract:
A stable formulation which is suitable for administration to animals is claimed. The formulation includes at least one active selected from the group comprising avermectins and milbemycins and levamisole. Both of the actives are dissolved in a pyrrolidone solvent.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to the field of veterinary pharmaceuticals and in particular to anthelmintic formulations including a combination of actives.  
       BACKGROUND  
       [0002]     Anthelmintics are an important tool for farmers seeking to improve the productivity of grazing cattle. The first class of modern broad-spectrum anthelmintic was the benzimidazoles introduced in the early 1960&#39;s, followed by levamisole and morantel in the late 1960&#39;s and finally the avermectins and milbemycins in the early 1980&#39;s.  
                                           Year of           Anthelmintic   Introduction   Main Active&#39;s in the Group                   Benzimidazoles   Early 1960&#39;s   Thiabendazole, albendazole,               fenbendazole, oxfendazole       Levamisole/Morantel   Late 1960&#39;s   Levamisole, morantel       Avermectins/Milbemycins   Early 1980&#39;s   Abamectin, ivermectin,               moxidectin, doramectin,               eprinomectin                  
 
         [0003]     Parasite resistance has developed to each group of anthelmintic since they were introduced. Resistance to benzimidazole-based drenches is widespread throughout the world. Cases have been reported that involve resistance in all three major cattle parasites species:  Ostertagia, Trichostrongylus  and  Cooperia.    
         [0004]     Resistance to levamisole/morantel based drenches is well known but is less widespread than benzimidazole resistance.  
         [0005]     In 1995, New Zealand researchers reported a strain of the worm parasite  Cooperia  that was resistant to both ivermectin (a member of the avermectin/milbemycin group) and to oxfendazole (a benzimidazole). In 1996, reports were published of an ivermectin resistant  Cooperia  strain that was cross-resistant to doramectin and moxidectin (also members of the avermectin/milbemycin group).  
         [0006]     To prevent and manage the problem of anthelmintic resistance farmers have relied on various number of strategies including: 
        minimizing anthelmintic use by only treating at strategically important times     alternating the type of anthelmintic used     using combinations of anthelmintics from different groups to reduce the potential of parasites to survive the treatment.        
 
         [0010]     Orally administered combinations of benzimidazole and levamisole anthelmintics are well known, and have been used for many years.  
         [0011]     However in recent years products based on actives selected solely from the avermectin/milbemycin groups have held the most significant share of the cattle anthelmintic market due to their high efficacy against the major production limiting parasite species,  Ostertagia.  The availability of easy to apply topical pour-on formulations has further extended their market dominance.  
         [0012]     By contrast, levamisole-based products have been used on a much more limited basis. Despite their having good efficacy against  Cooperia,  the key dose limiting parasite of the avermectin/milbemycin group.  
         [0013]     The table below shows that while each anthelmintic group has particular limitations against certain parasites, a combination of actives selected from the avermectin/milbemycin and levamisole groups would achieve two highly important goals: 
        high efficacy against the key cattle parasites        
 
         [0015]     combination potency to help prevent parasites surviving the treatment  
                                       Anthelmintic Class     Cooperia  Efficacy     Ostertagia  Efficacy                   Levamisole   Good   Poor       Avermectin/Milbemycin   Poor   Good       Combination of both classes   Good   Good                  
 
         [0016]     Despite this rationale for an easy to use product combining levamisole active with an avermectin/milbemycin active combinations have been difficult to formulate.  
         [0017]     Previous attempts included the formulation of a double active formulation including levamisole and niclosamide. This was designed to target tapeworm and roundworm. This formulation however, was unsatisfactory as exposure to water made it too viscous to use.  
         [0018]     Further it was found the differing pH requirements of levamisole and other anthelmintics made it difficult to formulate a stable product.  
         [0019]     NZ 336139 represents a recent attempt to formulate a combination avermectin/milbemycin and levamisole product.  
         [0020]     To achieve co-existance within the formulation Nufarm relies on emulsion technology. The emulsion includes formulation including the levamisole in aqueous acidic phase and including an anthelmintic such as an avermectin or milbemycin in the lipophilic phase. A third active can be suspended in particulate form in the aqueous phase.  
         [0021]     The disadvantage of this formulation is the need for the formulation to be shaken or agitated into an emulsion. In addition, the product is chemically complicated including 2 or 3 different phases.  
         [0022]     The complicated nature of the formulation in NZ 336139 is due in part to the different formulation requirements of the actives. Avermectins and milbemycins being substantially insoluble in water whereas levamisole is water soluble. In addition, levamisole has previously been found to require a pH of less than about 4 for stability while avermectins and milbemycin require a pH of about 6.6.  
         [0023]     As this will be appreciated, in addition to the stability issues topical formulations have a tendency to cause skin irritation to the animal at the site of application. Accordingly, a formulation to be acceptable for topical use it must not cause excessive skin irritation.  
         [0024]     Accordingly, there is a need for a stable, formulation capable of stably including avermectins or milbemycins together with levamisole.  
         [0025]     In addition, it is desirable the formulation be suitable for topical use.  
       OBJECT  
       [0026]     It is an object of the present invention to provide a stable anthelmintic formulation or one that will at least provide the public with a useful choice.  
       STATEMENT OF INVENTION  
       [0027]     In one aspect the invention relates to a stable formulation suitable for administration to animals including at least 2 actives wherein a first of the actives is selected from the group including the avermectins and the milbemycins and the second of said actives is levamisole, said actives being dissolved in a pyrrolidone solvent.  
         [0028]     Preferrably the formulation may additionally include a co-solvent selected from the glycol ether group.  
         [0029]     Preferably the avermectin or milbemycin is selected from the group including abamectin, doramectin, eprinomectin, ivermectin and moxidectin.  
         [0030]     Preferably the pyrrolidone solvent is N-methyl pyrrolidone or 2-pyrrolidone.  
         [0031]     More preferably the avermectin or milbemycin is present in the range of between 0.01 - 5% w/v.  
         [0032]     Preferably levamisole is present in the range of between 1 - 30% w/v.  
         [0033]     Preferably the formulation additionally includes at least one further medicament selected from the group comprising anthelmintics, dietary supplements, vitamins, mineral and other beneficial agents.  
         [0034]     More preferably wherein the formulation additionally includes excipients including preservatives, stabilisers, flavorants, co solvents.  
         [0035]     Preferably the formulation is suitable for topical, injectable or oral administration.  
         [0036]     More preferably the formulation is suitable for topical administration.  
         [0037]     More preferably the formulation does not cause unacceptable levels of skin irritancy when applied topically.  
         [0038]     In a further related aspect the invention relates to a method of treating or preventing infection of cattle with  Cooperia  or  Ostertagia  by administering a formulation of the present invention.  
         [0039]     The formulations of the present invention must be stable to be of commercial use. In this specification, a commercially acceptable anthelmintic formulation is one which is stable at room temperature for a period of at least 6 months. In conditions of accelerated testing, at 40° C., this requires the potency of the actives within the formulation to remain within specified and acceptable limits for 3 months.  
         [0040]     Avermectins and milbemycins where used in this specification refer to a group of actives having anthelmintic activity. The avermectin group includes by way of example, avermectin, ivermectin, doramection and eprinomectin. The milbemycin group includes moxidectin.  
         [0041]     Pyrrolidones solvents useable in this invention include, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1-pyrrolidone, N-ethylene-2-pyrrolidone, 3,3-dimethyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 5-dimethyl-2-pyrrolidone, N-ethoxy-2-pyrrolidone, and combinations thereof.  
         [0042]     Levamisole is used in this specification includes levamisole base, levamisole phosphate together with other salts and forms.  
         [0043]     The invention the subject of the present application is advantageous as it provides stable formulations including an avermectin or milbemycin in combination with levamisole. Further, the formulations retain each active in solution.  
         [0044]     The formulations are monophosic and suitable to manufacture on a commercial scale. In addition, as both actives are in solution the formulations are physically stable. in that it does not separate out into separate phases either aqueous and lipophilic phases or liquid and solid phases. This enables the formulations the subject of this application to ne used without requiring agitation or shaking before use and greatly reduces the risk of differing concentrations of actives through the drum or other storage container.  
         [0045]     In addition, as the formulation excludes water the issue of incompatible pH requirements is alleviated. Enabling the two actives to stability co-exist in a single phase. 
     
    
     DESCRIPTION  
       [0046]     A large number of studies were undertaken over a 4 year period to develop a stable anthelmintic formulation combining levamisole and avermectin/milbemycin. In these studies abamectin was used as the representative avermectin/milbemycin active, whilst levamisole, in its base form, was used as the representative levamisole/morantel active.  
         [0047]     Study 1  
         [0048]     A number of potential formulations were prepared using a soya bean oil base and common excipients used in the preparation of topical anthelmintics.  
                                                                                           Materials   % w/v                                    Formulation 1                Abamectin    1           Levamisole   20           Benzyl alcohol    5           Capmul PG-8   20           Isopropyl Palmitate   10           Tween 80    2           Soya bean oil   q.v.            Formulation 2                Abamectin    1           Levamisole   20           Benzyl alcohol    5           Capmul PG-8   20           Isopropyl Myristate   10           Tween 80    2           Soya bean oil   q.v.                      
 
         [0049]    
       
         
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Materials 
                 % w/w 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Formulation 3 
               
             
          
           
               
                   
                 Abamectin 
                  1 
               
               
                   
                 Benzyl alcohol 
                  5 
               
               
                   
                 Capmul PG-8 
                 20 
               
               
                   
                 Isopropyl Palmitate 
                 10 
               
               
                   
                 Tween 80 
                  2 
               
               
                   
                 Soya bean oil 
                 q.v. 
               
             
          
           
               
                 Formulation 4 
               
             
          
           
               
                   
                 Abamectin 
                  1 
               
               
                   
                 Levamisole 
                 20 
               
               
                   
                 Benzyl alcohol 
                  5 
               
               
                   
                 Capmul PG-8 
                 20 
               
               
                   
                 Isopropyl Myristate 
                 10 
               
               
                   
                 Soya bean oil 
                 q.v. 
               
               
                   
                   
               
             
          
         
       
     
         [0050]     None of these formulations were stable when tested under conditions of elevated temperature. All formulations exhibited significant degradation of the abamectin component. Animal studies also demonstrated an unexpected degree of skin irritancy with hair loss at the point of application. These results indicated that an oil-base to the product may be unsuitable both from an irritancy and stability perspective.  
         [0051]     Study 2  
         [0052]     A number of formulations were prepared using propylene glycol and glycol ethers, both common excipients used in veterinary drug formulation. These were then subjected to conditions of elevated temperature to determine their potential shelf stability. As a positive control for stability testing purposes a commercially available avermectin/milbemycin product, Ivomec® Plus Injection was used.  
         [0053]     Formulations  
                                                                                                                                                           Ivomec ®                                   Plus           R20   R27   R28   R29   Ivomec ®   Levipor ®   injection                                    Lev.base   20.0 g   20.0 g   20.0 g   20.0 g   —   20.0 g   —       Abamectin    1.0 g    1.0 g    1.0 g    1.0 g   —   —   —       Ivermectin   —   —   —   —    0.5 g   —    3.0 g       Propylene Glycol     50 g     41 g     50 g     41 g           Benzyl alcohol   —   —     10 g     10 g           BHT    0.2 g    0.2 g    0.2 g    0.2 g           IPA   —     4 g   —     4 g                *DGMEE to    100 ml    100 ml    100 ml    100 ml   * No more details                 *DGMEE: Diethylene glycol monoethyl ether (Transcutol ®)             
 
         [0054]     Stability Results  
                                                                                                         5 d/   10 d/   15 d/   20 d/   25 d/           0 day   60° C.   60° C.   60° C.   60° C.   60° C.                                    R20   Lev.base   100%   93.1%   92.0%   88.4%   84.9%   83.2%           Aba   100%   86.9%   67.0%   66.5%   46.9%   34.5%       R27   Lev.base   100%   88.1%   83.6%   83.8%   83.2%   79.9%           Aba   100%   80.7%   76.9%   67.2%   58.5%   37.6%       R28   Lev.base   100%   85.7%   82.1%   82.7%   79.5%   75.3%           Aba   100%   84.4%   64.4%   56.5%   45.2%   39.9%       R29   Lev.base   100%   88.3%   85.6%   88.3%   85.2%   81.3%           Aba   100%   92.2%   72.3%   63.9%   52.2%   44.5%       Ivomec ®   Ivermectin   100%   99.9%   —*   —*   —*   —*       Levipor ®   Lev.base   100%   82.0%   —*   —*   —*   —*       Ivomec ® Plus   Ivermectin   100%   97.9%   93.1%   91.7%   95.9%   90.7%       injection                       (?)                 *solvent evaporated             
 
         [0055]     In all test formulations at elevated temperatures the abamectin component degraded significantly over the period of the study. The ivermectin component of the commercially available Ivomec® Plus formulation did not deteriorate to anywhere near the same extent as the abamectin component of the test formulations.  
         [0056]     Whilst the levamisole component also deteriorated it did so at a much lower rate. The study once again demonstrated the difficulty of combining the two actives and that the presence of levamisole was very problematic in preparing the combination formulation.  
         [0057]     Study 3  
         [0058]     A further range of formulations were prepared in which benzyl alcohol was used to solubilise the abamectin component of the formulations.  
         [0059]     Formulations  
                                                                             Concentration (%, w/v)                        029/2/   029/3/   029/4/   029/5/       Ingredients   029/0   029/1   BHT   BHT   BHA   BHA               Lev.base   20.0   20.0   20.0   20.0   20.0   20.0       Abamectin    1.0    1.0    1.0    1.0    1.0    1.0       Propylene   41.0   41.0   41.0   41.0   41.0   41.0       Glycol       Benzyl   —   15.0   15.0   15.0   15.0   15.0       Alcohol       Isopropyl    4.0    4.0    4.0    4.0    4.0    4.0       myristate       BHT   —   —    0.2    1.0   —   —       BHA   —   —   —   —    0.2    1.0       Diethylene   100 ml   100 ml   100 ml   100 ml   100 ml   100 ml       glycol       monoethyl       ether to                  
 
         [0060]     Stability Results  
                                                                                                                 20 d/   25 d/   30 d/   1 Month/   2 Month/   3 Month/           0 day   60° C.   60° C.   60° C.   37° C.   37° C.   37° C.                                    029/0   Lev.base   100%    91.0%    90.1%    88.2%    95.0%   100.9%   ND                                   (?)               Aba   100%    43.5%    36.3%    28.7%    91.3%    79.9%   ND       029/1   Lev.base   100%    76.3%    78.7%    75.1%    96.3%    89.4%   ND           Aba   100%    42.3%    35.3%    31.5%   102.4%    65.8%   ND       029/2/BHT   Lev.base   100%    83.2%    74.4%    70.9%    95.4%   103.5%   ND                                   (?)               Aba   100%    45.3%    31.0%    31.8%    94.8%    62.8%   ND       029/3BHT   Lev.base   100%    84.1%    78.1%    70.2%    96.8%    90.8%   ND           Aba   100%    46.2%    36.1%    32.8%    96.2%    50.2%   ND       029/4/BHA   Lev.base   100%    82.8%    73.6%    73.2%    96.9%    91.7%   ND           Aba   100%    46.7%    34.9%    34.0%    96.5%    51.0%   ND       029/5/BHA   Lev.base   100%    85.0%    77.9%    74.5%   100.4%    94.1%   ND           Aba   100%    47.8%    36.9%    33.0%   100.9%    53.2%   ND       Ivomec ®   Iver   100%    95.0%    98.0%   101.3%   100.3%   100.3%   ND       Levipor ®   Lev.base   100%   102.0%   102.9%   100.9%   104.5%    94.9%   ND                  
 
         [0061]     In the stability study the presence of benzyl alcohol did not have any significant effect in minimizing the rate of degradation of the abamectin component of the formulations. BHA and BHT also did not offer any advantage as stabilizing aids.  
         [0062]     Study 4  
         [0063]     A study was undertaken to determine whether the use of propylene glycol or glycol ethers would have any advantage in stabilizing the formulations.  
         [0064]     Two formulations were prepared these are shown in the table below.  
         [0065]     Formulations  
                                                                     R 3   R 4                                        Levamisole base   20.0 g   20.0 g           Abamectin    1.0 g    1.0 g           Propylene glycol   —    40 ml           *DGBE to    100 ml    100 ml                         *DGBE: Diethylene glycol n-butyl ether (Butyl carbitol ®)             
 
         [0066]     Stability Results  
                                                                                                 5 d/   10 d/   15 d/   20 d/           0 day   60° C.   60° C.   60° C.   60° C.                                    R3   Lev.base   100%   98.2%    99.0%   104.3%   100.5%           Aba   100%   73.5%    67.3%    60.0%    52.8%       R4   Lev.base   100%   96.6%   100.6%    89.3%    95.5%           Aba   100%   67.8%    49.6%    33.5%    33.4%                  
 
         [0067]     While levamisole base was relatively stable in both formulations the abamectin degraded in both formulations with the rate of degradation much more significant in the formulation that included propylene glycol. This suggested that propylene glycol was probably not beneficial in enhancing the stability of abamectin when used with DGBE.  
         [0068]     Study 5  
         [0069]     A study was undertaken to attempt to improve the stability of formulations that used DGBE as their base.  
         [0070]     Formulations  
                                                                             3-1   3-2   3-3                                        Aba    1.0 g    1.0 g    1.0 g           Leva.base   20.0 g   20.0 g   20.0 g           BHT   —    0.2 g    2.0 g           *DGBE to    100 ml    100 ml    100 ml                         *DGBE: Diethylene Glycol n-butyl Ether             
 
         [0071]     Stability Results  
                                                                                             10 days/   20 days/   30 days/           0 days   60° C.   60° C.   60° C.                                        3-1   Lev.base   100%   94.2%   96.7%   92.8%               Aba   100%   68.8%   54.1%   40.1%           3-2   Lev.base   100%   96.8%   97.9%   91.5%               Aba   100%   75.1%   55.9%   33.5%           3-3   Lev.base   100%   98.0%   91.1%   89.6%               Aba   100%   73.9%   52.6%   41.1%                      
 
         [0072]     The study demonstrated that both BHT and BHA had no significant effect on enhancing the stability of the abamectin component of the formulation.  
         [0073]     Study 6  
         [0074]     Alternate formulations that used benzoic acid and/or BHT were prepared to evaluate their effects on the stability of DGBE based formulations.  
         [0075]     Formulations  
                                                                                                 R1   R2   R3   R4   R5   R6                                    Lev.base   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g       Abamectin    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g       BHT   —   —   —    0.2 g    0.2 g    0.2 g       Benzoic   —   0.05 g    0.2 g   —   0.05 g    0.2 g       acid       *DGBE to    100 ml    100 ml    100 ml    100 ml    100 ml    100 ml                 *DGBE: Diethylene Glycol n-butyl Ether             
 
         [0076]     Stability Results  
                                                                                                                 10 d/   20 d/   30 d/   1 Month/   2 Month/   3 Month/           0 day   60° C.   60° C.   60° C.   37° C.   37° C.   37° C.                                    R1   Lev.base   100%   100.4%    98.9%    99.0%    98.7%    98.2%    98.6%           Aba   100%    65.5%    46.1%    34.5%    88.4%    72.0%    50.6%       R2   Lev.base   100%    99.4%    98.7%    98.6%    97.9%    97.3%    96.6%           Aba   100%    59.5%    42.3%    36.6%    71.4%    62.7%    56.6%       R3   Lev.base   100%   100.2%   103.2%   101.3%   102.4%   101.2%   102.4%           Aba   100%    58.5%    39.1%    44.1%    85.3%    73.9%    62.8%       R4   Lev.base   100%   100.1%    98.7%    99.5%   100.2%   101.1%   100.2%           Aba   100%    67.5%    33.7%    24.1%    93.7%    62.2%    55.2%       R5   Lev.base   100%    99.6%    99.1%    98.4%    99.2%    98.9%    99.5%           Aba   100%    52.1%    39.0%    27.7%    79.0%    61.7%    55.2%       R6   Lev.base   100%   100.1%   100.7%    99.2%   103.4%   101.2%   101.1%           Aba   100%    53.5%    49.7%    39.9%    68.6%    62.1%    47.7%                  
 
         [0077]     The stability of Abamectin showed no improvement with the use of benzoic acid or BHT.  
         [0078]     Study 7  
         [0079]     A selection of new formulations that included other excipients with DGBE were prepared.  
         [0080]     Formulations  
                                                                                                                                                                                                                                                                                                                                         R3   R4   R5   R6                                    Lev.base   20.0   g   15.0   g   20.0   g   20.0   g            Lev.HCl   —   5.0   g   —   —            Aba   1.0   g   1.0   g   1.0   g   1.0   g            β-CD   0.5   g   —   —   —            Benzoic acid   —   —   5.0   g   —            Citric acid   —   —   —   3.0   g            Propylene   40   ml   40   ml   —   —       Glycol       Glycerin   30   ml   30   ml   —   —       Formal            Capmul   —   to 100   ml   —   —       MCM            DGBE   to 100   ml   —   to 100   ml   to 100   ml                 DGBE: Diethylene glycol n-butyl ether             
 
         [0081]    
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 R7 
                 R8 
                 R9 
                 R10 
                 R11-1 
                 R11-2 
                 R12 
                 R13 
                 R14 
                 R15 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Lev.base 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
                 20.0 g 
               
               
                 Aba 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
                  1.0 g 
               
               
                 TEA 
                 — 
                 — 
                 — 
                   1.0 ml 
                 — 
                 — 
                   1.0 ml 
                   1.0 ml 
                 — 
                 — 
               
               
                 EDTA 
                 — 
                 — 
                 — 
                 — 
                 0.01 g 
                 — 
                 0.01 g 
                 0.01 g 
                 0.01 g 
                 0.01 g 
               
               
                 EDTA- 
                 — 
                 — 
                 — 
                 — 
                 — 
                 0.01 g 
                 — 
                 — 
                 — 
                 — 
               
               
                 2Na 
               
               
                 BHT 
                 — 
                 — 
                 — 
                 — 
                  2.0 g 
                  2.0 g 
                  2.0 g 
                 — 
                  2.0 g 
                 — 
               
               
                 BHA 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  2.0 g 
                 — 
                  2.0 g 
               
               
                 Benzoic 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                  5.0 g 
                  5.0 g 
               
               
                 acid 
               
               
                 DGMEE 
                 to 
                 — 
                 — 
                 to 
                 to 
                 to 
                 To 
                 to 
                 to 
                 to 
               
               
                   
                  100 ml 
                   
                   
                  100 ml 
                  100 ml 
                  100 ml 
                  100 ml 
                  100 ml 
                  100 ml 
                  100 ml 
               
               
                 DGBE 
                 — 
                 to 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                   
                  100 ml 
                   
               
               
                 DPM 
                 — 
                 — 
                 to 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                   
                   
                  100 ml 
               
               
                   
               
               
                   TEA: Triethylamine; EDTA: Ethylenediaminetetraacetic acid; BHT: Butylated Hydroxy Tolueue; BHA: Butylated Hydroxyanisole; DGMEE: Diethylene glycol monoethyl ether; DGBE: Diethylene glycol n-butyl ether; DPM: Dipropylene glycol methyl ether    
               
             
          
         
       
     
         [0082]     Stability Results  
                                                                                             10 days/   20 days/   30 days/           0 day   60° C.   60° C.   60° C.                                        R3   Lev.base   100%    99.5%   100.9%   100.9%                               (?)               Aba   100%    58.7%    36.5%    37.8%           R4   Lev.base   100%    99.7%    98.8%    98.4%               Aba   100%    58.6%    35.5%    24.0%           R5   Lev.base   100%    99.5%    90.6%    70.0%               Aba   100%    76.2%    49.5%    42.7%           R6   Lev.base   100%    98.9%    69.5%    52.4%               Aba   100%    70.9%    64.7%    69.4%                               (?)           R7   Lev.base   100%   101.1%   100.6%   100.4%               Aba   100%    60.6%    36.5%    26.6%           R8   Lev.base   100%    99.9%   100.1%   101.0%               Aba   100%    64.2%    52.9%    40.4%           R9   Lev.base   100%   101.4%   100.2%    98.8%               Aba   100%    60.1%    55.4%    46.9%           R10   Lev.base   100%    94.0%    99.3%   101.7%               Aba   100%    52.0%    37.5%    25.6%           R11-1   Lev.base   100%   101.7%    99.2%    98.3%               Aba   100%    67.0%    40.2%    27.3%           R11-2   Lev.base   100%   106.9%   100.1%    97.8%                       (?)                   Aba   100%    63.3%    57.1%    38.8%           R12   Lev.base   100%    97.0%    98.8%   100.1%               Aba   100%    53.0%    33.5%    28.3%           R13   Lev.base   100%    94.9%    99.8%    99.8%               Aba   100%    53.3%    35.7%    28.2%           R14   Lev.base   100%    64.5%    89.4%    70.6%                           (?)                   Aba   100%    56.1%    38.4%    23.7%           R15   Lev.base   100%    79.7%    96.0%    82.9%                           (?)                   Aba   100%    67.6%    38.9%    30.2%                      
 
         [0083]     None of the formulations showed great promise in stabilizing the abamectin component of the formulations.  
         [0084]     Study 8  
         [0085]     A selection of new formulations that included other excipients with DGMEE were prepared.  
         [0086]     Formulations  
                                                                                                                 F1   F2   F3   F4   F5   F6   F7   F8                                    Lev.base   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g       Abamectin    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g       TEA   —     1.0 ml     1.0 ml   —     1.0 ml     1.0 ml   —   —       EDTA   —   —   —   —   —   —   0.01 g   0.01 g       H 2 O   —   —   —     10 g     10 g     10 g   —     10 g       BHT   —   —   —   —   —   —    2.0 g    2.0 g       BHA   —   —   —   —   —   —   —   —       Benzoic    5.0 g   —    5.0 g    5.0 g   —    5.0 g   —   —       Acid       DGMEE to    100 ml    100 ml    100 ml    100 ml    100 ml    100 ml    100 ml    100 ml                 TEA: Triethylamine; EDTA: Ethylenediaminetetraacetic acid; BHT: Butylated Hydroxy Toluene; BHA: Butylated Hydroxyanisole; DGMEE: Diethylene glycol monoethyl ether             
 
         [0087]     Stability Results  
                                                                                             10 days/   20 days/   30 days/           0 day   60° C.   60° C.   60° C.                                        F1   Lev.base   100%    99.6%    78.3%    63.8%               Aba   100%    69.5%    38.5%    30.3%           F2   Lev.base   100%   100.3%   100.3%   104.6%                               (?)               Aba   100%    73.7%    50.2%    27.2%           F3   Lev.base   100%    99.7%    99.9%    87.7%               Aba   100%    52.3%    49.8%    26.9%           F4   Lev.base   100%    34.4%    9.2%    8.2%                           (?)   (?)               Aba   100%    64.0%    52.8%    46.1%           F5   Lev.base   100%   100.2%    97.2%    47.7%               Aba   100%   32.7%   No peak   No peak           F6   Lev.base   100%    47.9%    40.1%    34.5%               Aba   100%    63.2%    55.5%    45.4%                      
 
         [0088]     Once again none of the formulations showed great promise in stabilizing the abamectin component of the formulations.  
         [0089]     Study 9  
         [0090]     Further alternate formulations were prepared according to table below.  
         [0091]     Formulations  
                                                                                                 R1   R2   R3   R4   R5   R6                                    Lev.base   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g       Abamectin    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g       Benzoic    5.0 g    5.0 g    5.0 g   10.0 g   —   —       Acid       Acetic acid   —   —   —   —    2.0 ml    4.0 ml       BHA   —   —    2.0 g   —   —   —       DGMEE to    100 ml   —   —   —   —   —       DGBE to   —    100 ml    100 ml    100 ml    100 ml    100 ml                 BHA: Butylated Hydroxyanisole; DGMEE: Diethylene glycol monoethyl ether; DGBE: Dithylene glycol n-butyl ether             
 
         [0092]     Stability Results  
                                                                                             10 days/   20 days/   30 days/           0 day   60° C.   60° C.   60° C.*                                        R1   Lev.base   100%   105.8%   85.5%    79.4%                       (?)                   Aba   100%    58.1%   38.2%    31.0%           R2   Lev.base   100%    98.9%   73.9%    68.4%               Aba   100%    71.1%   44.3%    43.6%           R3   Lev.base   100%    98.5%   73.5%    61.2%               Aba   100%    83.8%   47.7%    38.8%           R4   Lev.base   100%    90.7%   69.0%    50.6%               Aba   100%    53.1%   48.7%    40.6%           R5   Lev.base   100%   100.0%   99.1%   100.4%               Aba   100%    70.0%   48.5%    28.4%           R6   Lev.base   100%    99.8%   99.6%    99.3%               Aba   100%    57.6%   52.4%                         *The temperature in oven was changed into 55° C. after stored for 20 days.             
 
         [0093]     However none of these demonstrated great promise in stabilizing the abamectin component of the formulations.  
         [0094]     Study 10  
         [0095]     Example formulations were prepared according to the table below.  
         [0096]     Formulations  
                                                                                         R1   R2   R3   R4   R5                                    Lev.base   20.0 g   20.0 g   20.0 g   20.0 g   20.0 g       Abamectin    1.0 g    1.0 g    1.0 g    1.0 g    1.0 g       Acetic acid   —    2.0 ml    4.0 ml    6.0 ml   10.0 ml       *DGBE to    100 ml    100 ml    100 ml    100 ml    100 ml                 *DGBE: Diethylene glycol n-butyl ether             
 
         [0097]     Stability Results  
                                                                                             10 days/   20 days/   30 days/           0 day   60° C.   60° C.   60° C.                                        R1   Lev.base   100%   99%   97%   96%               Aba   100%   85%   79%   58%           R2   Lev.base   100%   82%   67%   50%               Aba   100%   76%   71%   51%           R3   Lev.base   100%   78%   60%   40%               Aba   100%   77%   72%   53%           R4   Lev.base   100%   52%   46%   23%               Aba   100%   88%   85%   78%           R5   Lev.base   100%   55%   46%   19%               Aba   100%   73%   67%   55%                      
 
         [0098]     Formulations containing acetic acid did not improve the stability of abamectin. However, the stability of levamisole base was adversely affected to a significant extent.  
         [0099]     Study 11  
         [0100]     A trial was carried out to determine whether the addition of varying levels of N-Methyl-2-Pyrollidone (Pharmasolv) to DGBE would enhance stability. All the formulations were kept at 60° C. and were analysed to assess the extent of degradation after 7, 14 and 30 days.  
         [0101]     Formulations  
                                                                                         G1   G2   G3   G4   G5                                    Lev.base   20.0%   20.0%   20.0%   20.0%   20.0%           w.v.   w/v   w/v   w/v   w/v       Abamectin   1.15%   1.15%   1.15%   1.15%   1.15%           w/v   w/v   w/v   w/v       DGBE   —     25%     40%   q/v.   q.v.               w/v   w/v           N-Methyl-2-   q.v.   q.v   q.v     25%   —       Pyrollidone                  
 
         [0102]     Stability Results  
                                                                                                                               Initial   7 days at 60° C.   14 days at 60° C.   1 month at 60°            Form.   Abamectin   Levamisole   Abamectin   Levamisole   Abamectin   Levamisole   Abamectin   Levamisole                    G1   96.12   101.43   93.04   95.55   89.57   89.75   79.13   86.95       G2   100.24   103.22   95.65   99.50   95.65   96.35   79.13   93.60       G3   103.30   102.58   93.91   97.00   87.83   95.20   66.96   92.85       G4   109.05   101.70   101.74   99.95   93.91   99.35   66.57   93.80       G5   89.42   100.32   83.48   97.80   80.00   93.30   57.39   89.55                  
 
         [0103]     The stability results of the solution containing both the actives in Pharmasolv demonstrated that surprisingly a pyrollidone based formulation was capable of significantly slowing the rate of degradation of both levamisole and abamectin.  
         [0104]     To further confirm the findings of this study new batches were prepared with the formulation as specified in the following table:  
                                                   Material   Formulation                           Lev.base   20.0% w/v           Abamectin   1.15% w/v           DGBE     25% w/v           N-Methyl-2-Pyrollidone   q.v                      
 
         [0105]     Stability results over a twelve month period of storage at 25° C. confirmed the increased stability of an abamectin/levamisole formulation containing N-Methyl-2-Pyrollidone (Pharmasolv) and DGBE.  
                                                           ACTIVE   Initial   6 Month   12 Months                           Abamectin   104.00   102.55   99.95           Levamisole    99.75    99.00   98.55                      
 
         [0106]     Field Studies  
         [0107]     The formulation of the table above containing DGBE and N-methyl-2-pyrollidone was used in a slaughter study to evaluate the effectiveness of the formulation relative to formulations containing either levamisole or an avermectin or milbemycin. The results clearly demonstrated that whilst the levamisole-based formulation (Levipor®) performed poorly against  Ostertagia  and the eprinomectin-based formulation (Eprinex®) performed poorly against  Cooperia,  the abamectin/levamisole combination showed outstanding efficacy against all parasite species.  
         [0108]     A large number of field studies on cattle of all ages have also confirmed that in contrast with a number of the other test formulations there is no skin irritation on treated animals.  
         [0109]     Table 1: Geometric mean total worm counts for calves treated with Abamectin/levamisole pour-on, Eprinex® pour-on or Levipor® pour-on in comparision with an untreated control group.  
                                                       Aba/Lev   Eprinex ®   Levipor ®       Treatment   Control   PO   PO   PO                     Ostertagia  (adult)   11435.5 a     4.4 b     17.3 b     5808.1 a           Ostertagia  (immature)   1274 a     2.3 b     0 b     1317.4 a           T .  axei  (adult)   996.7 a     0 b     0 b     110.9 a           T .  axei  (immature)   4.7 a     0 a     0 a     1.9 a           Trichostrongylus  spp   744.3 a     6.7 b     46.4 a     5 b         (mature)         Cooperia  (adult)   15948.8 a     1.9 b     2155.8 a     5.9 b           Cooperia  (immature)   1598.7 a     1.9 b     5.7 b     1.9 b           Oesophagostomum     2.5 a     0 a     0 a     0 a         (mature)         Trichuris  (mature)   35.4 a     0 b     0 b     0 b                     a means within the same row with different superscripts are significantly different at p &lt; 0.05             
 
         [0110]     Table 2: Treatment efficacies based on group geometric mean total worm counts.  
                                           Treatment   Aba/Lev PO   Eprinex ® PO   Levipor ® PO                     Ostertagia  (adult)   &gt;99.9%    99.8%    49.2%         Ostertagia  (immature)    99.8%   &gt;99.9%      0%         T .  axei  (adult)   &gt;99.9%   &gt;99.9%    80.1%         T .  axei  (immature)   &gt;99.9%   &gt;99.9%   &gt;99.9%         Trichostrongylus  spp    99.1%    93.7%    99.3%       (mature)         Cooperia  (adult)   &gt;99.9%    86.5%   &gt;99.9%         Cooperia  (immature)    99.8%    99.6%    99.9%         Oesophagostomum     &gt;99.9%   &gt;99.9%   &gt;99.9%       (mature)         Trichuris  (mature)   &gt;99.9%   &gt;99.9%   &gt;99.9%                  
 
       Preferred Embodiments  
       [0111]     In the preferred embodiments the formulations of the invention there include avermectin or milbemycin in combination with levamisole and a pyrrolidone solvent. A glycol ether may additionally be included.  
         [0112]     The following examples are provided as examples only and are in no way intended to limit the spirit or scope of the invention.  
       EXAMPLE FORMULATIONS  
       [0113]     The formulations of the present invention are prepared as follows:  
         [0114]     1. Add levamisole base, avermectin/milbemycin and pyrollidone to a mixing vessel.  
         [0115]     2. Stir at room temperature until the actives have completely dissolved.  
         [0116]     3. Add the glycol ether, if desired, and mix well.  
         [0117]     4. Add the pyrolidone to volume and continue mixing until a clear solution is obtained.  
         [0118]     Topical Formulations  
         [0119]     1. Examples of topically applied formulations of the invention include:  
         [0120]     Formulation 1.1  
                                                   Ingredient   % w/v                           Abamectin    1%           Levamisole Base   20%           n-methyl pyrrolidone   q.v.                      
 
         [0121]     Formulation 1.2  
                                                   Ingredient   % w/v                           Ivermectin   0.5%           Levamisole Base    10%           n-methyl pyrrolidone   q.v.                      
 
         [0122]     Formulation 1.3  
                                                   Ingredient   % w/v                           Ivermectin   0.5%           Levamisole Base    10%           DGMBE    25%           n-methyl pyrrolidone   q.v.                      
 
         [0123]     Formulation 1.4  
                                                   Ingredient   % w/v                           Eprinomectin   1.0%           Levamisole Base    20%           DGMBE    25%           n-methyl pyrrolidone   q.v.                      
 
         [0124]     2. Examples of Injectable formulations include:  
         [0125]     Formulation 2.1  
                                                   Ingredient   % w/v                           Ivermectin   0.5%           Levamisole Phosphate    20%           2- pyrrolidone   q.v.                      
 
         [0126]     Formulation 2.2  
                                                   Ingredient   % w/v                           Moxidectin   0.5%           Levamisole Phosphate    20%           2 - pyrrolidone   q.v.                      
 
         [0127]     3. Examples of Orally administered formulations include:  
         [0128]     Formulation 3.1  
                                                   Ingredient   % w/v                           Abamectin   0.1%           Levamisole Base     5%           n-methyl pyrrolidone   q.v.                      
 
         [0129]     Formulation 3.2  
                                                   Ingredient   % w/v                           Ivermectin   1%           Levamisole Base   5%           n-methyl pyrrolidone   q.v.                      
 
         [0130]     Formulation 3.3  
                                                   Ingredient   % w/v                           Abamectin    1%           Levamisole Base   20%           n-methyl pyrrolidone   q.v.                      
 
         [0131]     Formulation 3.4  
                                                   Ingredient   % w/v                           Abamectin    1%           Levamisole Base   20%           n-methyl pyrrolidone   q.v.                      
 
         [0132]     Formulation 3.5  
                                                   Ingredient   % w/v                           Abamectin    1%           Levamisole Base   20%           n-methyl pyrrolidone   q.v.                      
 
         [0133]     The rates for these formulations are generally in the order of 1 ml to 5 kg to 1 ml per 20 kg for oral administration, 1 ml per 25 kg or 1 ml per 50 kg for administration by injection, and 1 ml per 10 kg or 1 ml per 20 kg for topical administration.  
         [0134]     The methods of administration of the formulations are well known within the art.