Abstract:
A cartridge and system are described for automatically metering a predetemined dosage of a medicament. The cartridge includes a tab on its exterior, and a dispensing gun which receives the cartridge has a detent for stopping forward movement of the upper end of a trigger when the detent contacts the tab on the cartridge. When the detent contacts the tab on the cartridge, no further medicament can be dispensed on that stroke of the trigger.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon, and claims the benefit of, our U.S. Provisional Application Ser. No. 60/093,166, filed Jul. 17, 1998. 
    
    
     BACKGROUND 
     1. Field of Invention 
     This invention relates to multidose, medical injection syringes used for the vaccination and treatment of livestock diseases. More specifically, it relates to a process and a closed handling and delivery system for those injectable animal health products used in syringes and how the dosage level administered to the patient is controlled or metered. 
     2. Description of Prior Art 
     Generally speaking, in multidose, pistol grip livestock syringes, the precise metering of the dosage dispensed is accomplished by restricting the stroke of the plunger rod. Heretofore, the stroke of the plunger rod has been controlled by mechanical systems incorporated into the syringe body and trigger mechanisms. Original designs of pistol grip syringes commonly include ratchet and pawl mechanisms, wherein the trigger is squeezed and a pawl attached to the trigger engages a ratchet, formed on the plunger rod. The plunger rod is then advanced forward to dispense the medicament from the barrel of the syringe. 
     Metering is accomplished by an adjustable stop attached to either the trigger, as is demonstrated in U.S. Pat. No. 3,110,310 to Cislak (1963), or to the syringe body as is shown in U.S. Pat. 4,014,331 to Head (1977). The adjustable stop restricts the forward movement or stroke of the plunger rod, therefore metering the amount of medicament dispensed. Similar mechanisms for dosage metering are employed when pre-filled cartridges are used with pistol grip syringe bodies as is shown in U.S. Pat. No. 4,738,664 to Prindle (1988) and U.S. Pat. No. 3,517,668 to Brickson (1967). 
     Phillips et al. (1988), in U.S. controlled by a threaded adjustment on the anterior end of the syringe body. Other known cartridge type systems generally utilize a single dose system wherein one full squeeze of the trigger dispenses the entire contents of the cartridge as is shown in U.S. Pat. No. 4,576,591 to Kaye et al. (1986) and U.S. Pat. No. 4,968,303 to Clarke et al. (1990). 
     With those methods of dosage metering, the amount of medicament dispensed from a multi-dose cartridge is determined by a setting or an adjustment made to the syringe or applicator by the technician. Mechanical dosage settings are often bumped or may slip to the next setting so that many animals may be injected with the improper dosage before the mistake has been detected and the correction is made. It is also not uncommon for the technician to accidentally set the dosage adjustment to an improper setting. Most medicaments have a prescribed dosage level, which technically could eliminate the need for dosage adjustment by the technician. 
     There has not heretofore been provided a self-metering cartridge system or a system for automatically metering a predetermined dosage of a medicament from a cartridge. 
     SUMMARY OF THE PRESENT INVENTION 
     Dosage levels for most medicaments, particularly vaccines, are constant and prescribed by the manufacturer of the vaccine. As an example, a vaccine for the prevention of X disease may require a 5 milliliter dose while a different vaccine for Y disease may prescribe a 2 milliliter dose. In our self-metering cartridge system, all syringe bodies are capable of dispensing any dosage level up to the largest dosage that may be prescribed. The self-metering cartridge will dictate the length of the stroke of the plunger rod therefore dictating the dosage level of the medicament dispensed with each squeeze of the trigger. 
     In practice, a 2-milliliter dose product will be packaged in a self-metering cartridge that will restrict the forward movement of the plunger rod and allow precisely 2 milliliters of medicament to be dispensed from the cartridge. Similarly a 5-milliliter dose self-metered cartridge will stop the forward movement of the plunger rod when 5 milliliters of medicament have been dispensed from the cartridge. If the loaded cartridge in the chamber is not equipped with the self-metering aspect, a full squeeze of the trigger will allow the plunger rod to advance as far forward as is mechanically possible. That full squeeze will dictate the largest dosage that the syringe is capable of administering. As an example, an unrestricted full squeeze may dispense 10 milliliters of medicament. 
     The advantage to the self-metering cartridge is that no human error or mechanical malfunction of an adjustable metering mechanism can cause the syringe to give an improper dosage. Even if the wrong medicament has been accidentally loaded into the syringe, the proper dosage for that particular medicament will be given. In addition, the stop mechanism for metering the dosage level has bene simplified to no adjustable or moving parts. When a cartridge is loaded into the barrel of a syringe body, the metering is automatic and specific to the product contained in the cartridge. 
     Other features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a pistol grip syringe body with the trigger in the resting position; 
     FIG. 1A is an enlargement of a portion of FIG. 1; 
     FIG. 2 shows the syringe body of FIG. 1 with the trigger in the squeezed position; 
     FIG. 2A is an enlargement of a portion of FIG. 2; 
     FIG. 3 is the cartridge with the metering tab; and 
     FIG. 4 is a ¾ exploded view of the syringe body, cartridge and self-metering components. 
    
    
     REFERENCE NUMERALS IN DRAWINGS 
       10   a  syringe body frame, right half 
       10   b  syringe body frame, left half 
       12  syringe body barrel 
       14  syringe body handle 
       16  self-metering cartridge 
       18  cartridge metering tab 
       20  trigger 
       20   a  lower trigger 
       20   b  upper trigger 
       22  trigger pivot 
       24  moveable metering rod 
       26  metering rod hinge point 
       28  plunger rod 
       30  drag link 
       32  plunger 
       34  tear away foil seal 
       36  standard rubber stopper 
       38  standard aluminum stopper seal 
     DETAILED DESCRIPTION OF THE INVENTION 
     The essence of this invention combines the mechanical aspects of the items shown in FIGS. 1 through 4 to complement the systems described in U.S. Pat. No. 5,733,258 and application Ser. No. 08/532,055, incorporated herein by reference. The goals of this self-metering cartridge are as follows: 
     (a) simplify the mechanism to automatically meter the dosage given by this syringe and cartridge system. 
     (b) eliminate the need to preset or adjust the syringe to meter the dosage to be given. 
     (c) eliminate the chance of human or mechanical error often associated with mechanical hand adjustments of the syringe to meter the dosage levels. 
     (d) transfer the responsibility of dosage metering from the syringe body to the cartridge. Therefore, a medicament will be packaged into a self-metering cartridge, pre-set to the dosage level prescribed by the manufacturer of the medicament. No adjustments need to be or can be made by the technician administering the medicament to the livestock; therefore, the proper dosage level is always given. 
     (e) reduce the cost to manufacture the metering devise in the syringe. 
     A preferred embodiment of the self-metering cartridge is illustrated in FIG. 1 through 4. The disposable, self-metering cartridge  16 , as shown in FIG. 3, is a cylindrical hollow tube made of a durable or unbreakable, plastic-like substance. The anterior end is necked down to form a standard vaccine-type bottle-filling head. the filling head is plugged with a standard rubber-like stopper  36  and sealed with a standard aluminum stopper seal  38 . The medicament is sealed into the cartridge  16  at the posterior end by the plunger  32 . 
     A tear away foil seal  34  is applied to the extreme posterior end of the cartridge  16 . the cartridge  16  is molded with a cartridge metering tab  18  on the external surface running parallel to the longitudinal axis of the cartridge  16 . The placement of the metering tab  18  on the cartridge  16  dictates the distance the trigger  20  may travel with one full squeeze of the lower trigger  20   a , which, in turn, dictates the forward movement of the plunger rod  28 . Forward movement of the upper trigger  20   b , is transferred to the plunger rod  28  by the drag link  30 . The distance the plunger rod  28  may travel dictates the dosage level of medicament dispensed from the cartridge  16 . The moveable metering rod  24  is hinged at point  26  on the upper trigger  20   b  and transfers the movement of the upper trigger  20   b , to the metering tab  18 . when the moveable metering rod  24  strikes the metering tab  18 , the forward movement of the upper trigger  20   b  and the position of the trigger  20 , the drag link  30  and the moveable metering rod  24 , all in the resting position. FIG. 2 demonstrates the position of those components in the compressed position i.e., with the lower trigger  20   a  pulled rearwardly toward the syringe body handle  14 . FIG. 4 is an exploded view of the syringe body, cartridge and self-metering components which serves to illustrate the design of those major components associated with the function of the self-metering cartridge. 
     Operation of Structures of FIGS. 1 to  4   
     The tear away foil seal  34  is removed from the posterior end of the cartridge  16  and the pre-filled self-metering cartridge  16  is breech loaded into the syringe body barrel  12  and snapped to the closed position to the main syringe body frame  10   a  and  10   b.  To administer a dose of medicament the lower trigger  20   a  is squeezed or compressed to the syringe body handle  14 . As the trigger  20  rotates on the trigger pivot  22 , the upper trigger  20   b  moves forward, pushing the drag link  30  forward. the forward angular movement of the drag link  30  creates a bind on the plunger rod  28  and drags the plunger rod  28  forward. The forward movement of the plunger rod  28  pushes the plunger  32  forward in the cartridge  16 , forcing the medicament from the cartridge  16  through an adapted needle, pierced into the stopper  36  at the anterior end of the cartridge  16 . The moveable metering rod  24  is hinged to the upper trigger  20   b  at the metering rod hinge point  26 . When the trigger  20  is compressed, the moveable metering rod  24  is advanced forward until it makes contact with the cartridge metering tab  18 . This contact stops the forward movement of the entire trigger mechanism including the moveable metering rod  24 , the trigger  20 , the drag link  30 , the plunger rod  28  and the plunger  32 . thus the positioning of the metering tab  18  along the longitudinal axis of the cartridge  16  determines the travel from the self-metering cartridge  16 . The metering rod  24  serves as a detent means for stopping forward movement of the plunger  32  when rod  24  strikes tab  18  on the cartridge  16 . Other types of detents could be used, if desired. 
     The use of this self-metering cartridge of the invention is a tremendous improvement over the current state of the art dosage metering mechanisms available conventional in pistol grip syringes. The advantages listed below become apparent to anyone who has given injections to livestock. 
     No complicated adjustable metering mechanisms need to be incorporated into the construction of the syringe body. 
     There is no chance of the metering adjustment skipping or being bumped into a different setting. 
     The possibility of the technician accidentally dialing an improper setting on a metering adjustment is eliminated. 
     The dosage level for the medicament is preset and automatic in the cartridge by the manufacturer of the medicament. Therefore, the manufacturer can rest assured that the proper dosage levels of their products are being administered. 
     Farm and ranch managers can also rest assured that their employees are administering the proper dosage levels of these expensive medicaments. 
     Although some example specifications are implied throughout the text of the above descriptions, these should not be construed as limiting the scope of the invention but as merely providing illustrations so that the reader may visualize the embodiment of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.