Abstract:
Solid dose ballistic projectile for medicating animals which comprises a biologically compatible projectile casing which defines an interior cavity having a wall with a frictionally engagement enhanced surface. A medicament payload, slightly oversized with respect to the cavity, is forced into the cavity engaging the frictionally-enhanced cavity surface for a tight, secure fit. The bullets are of improved accuracy and can be successfully implanted into the flesh of an animal with greater reliability.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a ballistic implant for successfully administering solid biologically active medicaments to domesticated livestock such as cattle and hogs, and in wild animals. 
     BACKGROUND OF THE INVENTION 
     Solid dose ballistic projectiles shaped for penetrating the epidermal layer of living animal tissue are known. They lodge totally within the tissues of the animal for later release of biologically active medicaments into the animal&#39;s tissue. “Solid dose” in this context therefore refers to the fact that the body of the projectile is made entirely of a mixture comprising biologically inert, usually soluble and/or biodegradable materials, encasing a biologically active medicament dose, commonly referred to as “the payload”. 
     Such bullets are used not only for domesticated livestock, but often for inoculating wildlife as well. They are particularly advantageous over administering typical liquid vaccines in that the animals do not have to be captured, thus avoiding the traditional time-consuming and costly necessity of gathering and treating the animals. Such herding also often causes animal stress resulting in weight loss, and even death in some animals. 
     Since it is well known that inoculations under physiological stress are often less effective than when applied to a relaxed animal, ballistic dose administration (using air guns to implant a medicament dose with a biologically inert bullet) has been developed. For examples of ballistic implants, see U.S. Pat. Nos. 3,948,263; 3,982,536; 4,326,524; 4,449,982; and 4,664,664. All of these have in common the use of a projectile, usually shot from an airgun. It penetrates, say 1-5 centimeters into the animal&#39;s muscle tissue, where it begins to be reconstituted with the animal&#39;s body fluids, usually disintegrating within a few hours, leaving no lasting tissue damage. 
     While ballistic implants have achieved some degree of success, due to their overcoming the need for gathering and herding of the animals, they have not achieved the degree of commercial success one might expect. This is so because of certain deficiencies, particularly in accuracy, with the currently-used ballistic implants. 
     Inaccuracy, that is, failure of the projectile to shoot where the gun is aimed causing “misses”, wastes medicament, and therefore increases significantly veterinary medicine expense. Moreover, with poor accuracy there is a risk of bullets hitting the animal in areas where the bullet may cause harm (e.g., head, spine, thorax, chest), or in areas where the bullet will not successfully penetrate muscle tissue, such as forelegs and the like. 
     It can be seen, therefore, that there is a real and continuing need for the development of a ballistic implant of increased accuracy. Doing so would allow successful implanting of medicament at less expense without active drug waste. This invention has as its objective the fulfillment of this need. 
     SUMMARY OF THE INVENTION 
     A solid dose ballistic implant for vaccinating or medicating animals. It comprises a biologically inert tissue compatible bullet which defines an interior cavity having a wall with a frictionally enhanced engagement surface. A cylindrical medicament payload, slightly oversized with respect to the dimensions of the interior cavity, is force fit into the interior cavity, engaging the frictionally-enhanced cavity surface for a tight, secure fit. The resulting ballistic implants are of improved accuracy and can be successfully implanted into the flesh of an animal with greater reliability and less drug waste. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of the projectile and the dosing medicament payload. 
     FIG. 2 is a longitudinal section along line  2 — 2  of FIG. 1 showing the construction of the projectile and its interior cavity. 
     FIG. 3 is a rear end view of the projectile with the interior cavity loaded with medicament payload. 
     FIG. 4 is a front end view of the projectile. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     While the description here is given as a preferred embodiment of the invention, it is to be understood that the invention is not limited to the preferred embodiment only. Rather, the invention is limited only by the defining limits of the claims, as opposed to any statements in this specification relating to the preferred embodiment. 
     While trying to develop a projectile of increased accuracy, applicant tried several things, all of which one would logically think of as possibilities to increase bullet accuracy. For example, applicant tried form fitting the payload into the cavity, providing a cylindrical payload narrower than the cavity, providing a polymer-sealed narrower payload, providing a rounded back portion of the projectile, as well as different shaped projectile noses. None solved the accuracy problem. Rather, almost by serendipity, applicant discovered that oversized payloads force fit into the cavity of the projectile casing, with the walls of the interior cavity having a surface designed for frictional engagement enhancement, provides for a tight bullet, i.e., the payload and the molded casing move as a single unit, even when shot. This results in target-accurate shots. In particular, and with reference to the drawings, there is shown a cylindrical style projectile  10  having a body portion  12  defining an annular exterior wall  13  with a conical bullet nose or tip  14  terminating at its apex  16 . Annular wall  13  defines an interior cavity  18  and a rear or base portion  20 . Projectile  10  can be made of any inert material which is capable of being projected with sufficient force to penetrate a living animal body, and maintain its dimensional stability and its integrity on impact and entry of the animal muscle tissue. In order to not cause local tissue reactions, the projectile  10  must be made of biologically inert material. Mostly, such materials should be on the Generally Recognized As Safe, or “GRAS” list. Preferably, projectile  10  should be made of a polymeric blend which will disintegrate after penetrating usually 1-5 centimeters into the animal&#39;s muscle tissue. Usually, projectile casings will disintegrate in a few hours, and almost always by 24 hours. A suitable class of GRAS polymers which can be used are cellulose derivatives such as the nonionic water-soluble cellulose ether, hydroxypropylcellulose. Often the casing contains fillers such as calcium carbonate, and a small amount of lubricant such as, for example, stearic acid. 
     Suitable polymeric binders for inclusion in the mixture are biologically inert materials having characteristics which enable them to impart cohesiveness to the mixture. Preferably, the binder is a thermoplastic material, and the fillers and lubricant thermoplastically stable. Moreover, the binder must be cohesive, that is, it must adhere to other solid particulate ingredients and provide the mixture with a degree of cohesiveness. The binder may have the additional feature of acting as a disintegrant. By proper selection of the binder, the disintegration rate can be controlled to supply the biologically active ingredient in a sustained release or in a quick release manner. 
     Polymeric binders which have the above-described characteristics, and which enable quick release of the medicament, and are therefore preferred, include such water soluble materials as hydroxypropylcellulose, hydroxypropylmethylcellulose, methylcellulose, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, gum arabic, etc. Hydroxypropylcellulose is a particularly preferred binder due to its compatibility with biological systems, its cohesive characteristics, and its thermoplasticity. 
     Binders which have the required characteristics and are suitable for use in sustained release formulations include such nonpolar-solvent soluble materials as polylactic acids and polyamides, such as polyglycine. 
     It is to be appreciated that by mixing sustained release and quick release binders, a wide range of dissolution rates can be achieved. 
     The present invention does not reside so much in the material from which the projectile casing is made, but rather in the particular constructional features of the ballistic implant to provide improved accuracy. While some composition description has been provided, for further details of the bullet formulations, see the earlier-referenced patents, each of which are incorporated herein by reference. 
     The payload  22  of the ballistic implant is a solid dose medicament. Again, such solid dose medicaments are known, and reference is again made to the above-mentioned patents. However, generally the solid payload may be comprised of adjuvants conventionally employed in preparing tablets by direct compression, such as lubricants, disintegrants, fillers, and of course; the solid medicament. Useful solid particulate biologically active medicaments that may be used in preparations of the present type include hormones, minerals, vitamins, antibiotics, antigens, antibodies, and other medicinals, such as tranquilizers and dewormers. 
     With reference to FIG. 2, the interior wall  24  of cavity  18  can be seen. As illustrated, interior wall  24  has a series of parallel annular puller rings. Puller rings are concentric parallel ridges  28  which can be made by the core pins and dies used in making the projectile casing, usually by an injection molding or casting process. While annular ridges  28  of puller rings are shown, in fact, any means of raising projections for frictional engagement enhancement of the inner wall  24  surface of the interior cavity  18  can be utilized. Conceivably, any non-smooth discontinuity, in the form of which provide a frictionally engagement enhancing surface, would suffice. Examples might include ridges, bumps, nodules, grooves, etc. 
     Certain constructional features may be worthwhile to mention specifically. Typically, for ballistic implanting, applicant has found a standard  25  caliber bullet suitable. Length of the bullet doesn&#39;t appear critical. Bullets of 0.577 inches, 0.658 inches and 0.825 inches all seem to work, with longer bullets providing best accuracy. Preferred dimensions are the following: ID=0.160″ (+0.003″,−0.000″); OD (flat to flat)=0.2535″±0.001″; OD (spine to spine)=0.2635″±0.001″; Core depth: 0.260″; 1 in 7 or 1 in 6 twist. 
     Back, or base  20  of the ballistic implant is typically either flush, or more preferably, concave for enhanced accuracy. 
     The payload  22  is force fit into cavity  18  from the back  20 . For example, on the illustrated bullet  10 , assume the ID is 0.160″. Critical to force fitting the payload  22 , is that it be slightly oversized. For example, a high degree of success and accuracy was achieved if one used payloads of 0.163″ diameter. These pellet payloads insert readily when uniformly forced, and fit snugly without expanding the OD of the bullet. They fit snugly without any slop because they are force fit, and because they are compressed against frictionally engagement enhanced surfaces of puller rings such as by ridges  28 . 
     Surprisingly, when these force fit ballistic implants hereinafter are shot, increased accuracy and increased range are achieved. Moreover, various length bullets can be used, as earlier explained, and payloads having a weight of from 90 mg to 150 mg or more can be successfully used with the 25 caliber bullet without varying the accuracy. 
     EXAMPLE 
     The following example is offered to illustrate accuracy of the new bullets using the frictional engagement enhanced interior cavity surface as opposed to bullets of compatible, lesser diameter payload. 
     In particular, a crimped-back bullet casing containing a placebo of lesser diameter (0.156″) than the ID (0.160″) of the cavity was used for a series of shots at paper targets. The caliber was 25. In comparison, when identical  25  caliber bullet casings were used in the present invention, the shot grouping was far narrower, and less random, indicating higher accuracy. Table I shows the results. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 ACCURACY COMPARISON 
               
             
          
           
               
                   
                 Pellet Diameter 
                 Shot Grouping* (n = 5) 
               
               
                   
                   
               
               
                   
                 0.156″ 
                 10.5 cm 
               
               
                   
                 0.163″ 
                  4.0 cm 
               
               
                   
                   
               
               
                   
                 *Farthest distance apart  
               
               
                   
                 NOTE  
               
               
                   
                 Ballistic device “fixed” in a vise at a distance of 20′ from the target for this experiment.  
               
             
          
         
       
     
     It therefore can be seen that the invention accomplishes at least all of its stated objectives.