Abstract:
A syringe-type injection device for dispensing a preset dose of a liquid drug includes two sleeve-like components releasably connected with each other so as to be aligned in axial direction. One of the sleeve-like components is a holder for a dispensing mechanism and the other of the sleeve-like components is adapted to accommodate an ampoule and a cannula. The dispensing mechanism includes an axially movable piston rod for actuating a plug of the ampoule. The piston rod has a radially projecting cam follower and the holder defines at least one axially extending slot having a predetermined length, wherein the cam follower is received by the at least one slot, such that only a single dose can be dispensed from an ampoule by an axial movement of the piston rod.

Description:
This is a continuation-in-part of Ser. No. 07/499,527, filed Jul. 10, 1990, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a syringe device for dispensing a preset dose of a liquid drug. 
     2. Description of the Prior Art 
     A syringe device of this type is known from WO 87/02895. This device consists of two sleeve-like housing sections which can be connected together, where the syringe ampoule is screwed into the lower housing section when it is to be used. The drug dose to be dispensed can be preset manually. 
     The disadvantage of this and other similarly constructed devices in accordance with the state of the art is that they can only be used for drugs for which multi-shot dispensing from any one ampoule is permissible and usually also desirable. 
     For the treatment of male erection disorders the drug Papaverin is placed in ampoules without any preservatives, which is why only single-shot dispensing of the drug can be permitted to ensure sterility is maintained. 
     The dosage varies, depending on the severity of the condition, between 0.25 and 2.0 ml, i.e. if 0.25 ml is dispensed the remaining 1.75 ml is discarded. 
     This demand pattern cannot, however, be met by conventional dosage aids (PEN syringe devices). 
     DESCRIPTION OF THE INVENTION 
     It is the intention of the invention to improve on this situation. The object of the invention is to create a syringe device which can be pre-programmed by the doctor to dispense a fixed single-shot dose which cannot be altered by the patient. 
     The invention meets the task set by means of a syringe device in which the dispensing system is designed such that only a single dose can be dispensed from any one ampoule. 
     The advantages offered by the invention lie principally in the fact that, thanks to the syringe device in accordance with the invention, maximum security of operation is guaranteed, since the dispensing of a second dose of the drug, whether intentional or otherwise, is impossible. 
     A preferred embodiment is characterised therein that the dispensing mechanism comprises a piston rod with a piston rod neck, a dose ring, a retaining spring and a dosing button cap, and the dispensing mechanism is connected by means of a cap with the mechanism holder such that it cannot be disengaged. 
     In a further embodiment of the syringe device the piston rod consists of an inner hollow cylinder bearing the piston rod neck and, formed integrally with this inner hollow cylinder, of an outer hollow cylinder which has a cam follower on its outer sleeve surface. 
     A syringe device is particularly preferred in which the interior of the sleeve-like mechanism holder is provided with longitudinal slots of varying length in which a corresponding cam follower of the piston rod can slide. The longitudinal slots are preferably configured equidistantly and preferably with increasing length around the periphery of the inner sleeve of the mechanism holder housing. The ampoule is preferably connected to the ampoule sleeve such that it is difficult to disengage. 
     A further embodiment of the syringe device is characterized therein that a dose ring is firmly connected radially to the piston rod preferably by means of cam/slot couplings and is provided on its outer periphery with a scale. The housing of the mechanism holder preferably has a window through which the dose ring scale can be viewed from outside. 
     The housing is advantageously manufactured from an optically opaque material, for example polyamide. 
     An embodiment of the invention which at the same time serves to explain the operating principle is described in further detail below and is illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a meridional section through the syringe device according to the invention; 
     FIG. 2 shows a cross-section along the line II--II in FIG. 1; 
     FIG. 3 shows a cross-section along the line III--III in FIG. 1; 
     FIG. 4 shows a perspective view of the syringe device in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The syringe device according to the invention illustrated in longitudinal section in FIG. 1 consists essentially of two sleeve-like components 1, 10 which can be connected together, one of which is designed as the holder 1 for the dispensing mechanism 20 and the other as the ampoule sleeve 10 to accommodate the ampoule 11 and the cannula 12. The assembled syringe device which is held together by the cap 6 can be carried like a fountain pen by means of the clip 8 (FIG. 4). The dispensing mechanism 20 consists of a cylindrical piston rod 2 with an inner hollow cylinder 23 bearing the piston rod neck 4 and, formed integrally with this inner hollow cylinder 23, of an outer hollow cylinder 24 which has a cam follower 16 on its outer sleeve surface (FIG. 2). Externally the dispensing mechanism is designed as a manually operable dosing button 7. When the syringe device is assembled, the dispensing mechanism 20 acts by means of the piston rod neck 4 on the base of the ampoule plug 15 of the drug ampoule 11. 
     The ampoule sleeve 10 consists of a housing 25 which accommodates the ampoule 11 and can be firmly connected by means of a coupling (not shown) to the housing 22 of the mechanism holder 1. The cannula 12 which connects with the ampoule 11 is protected against damage by means of the inner protective cap 13 and the outer packing sleeve 14. 
     The detailed description given below, especially of the dispensing mechanism 20 with reference to the cross-sectional drawings of FIGS. 2 and 3, also serves to describe the operation of the syringe device in accordance with the invention. 
     A dose ring 5 is firmly mounted radially on the outer hollow cylinder 24 by means of cam/slot couplings 19 such that the ring 5 also turns if the dispensing mechanism 20 is rotated. A scale 21 located on the outer periphery of the dose ring 5 can be read through a window 18 in the housing 22 of the mechanism holder 1 (FIG. 3). 
     The dispensing mechanism 20 is located such that it can move longitudinally by means of the retaining spring 3 in the mechanism holder 1 which is formed as a hollow cylinder and held in place by the cap 6 which can be screwed onto the housing 22 of the mechanism holder 1. In FIG. 1 the default position of the dispensing mechanism 20 is depicted in which the dose ring 5 lies flush against the screwed-on cap 6 as a result of the force of the retaining spring 3 acting on the dispensing mechanism. 
     The interior of the housing 22 of the mechanism holder 1 is provided with longitudinal slots 17 of varying length in which the appropriate cam followers 16 of the dispensing mechanism 20 can slide. 
     The stroke of the dispensing mechanism 20 and thus the drug dose which can be discharged is therefore determined by the length of the longitudinal slot 17 in conjunction with the cam follower 16. If the cam follower 16 slides in a short longitudinal slot 17, as illustrated in FIG. 1, the drug dose is small, whereas if the cam follower 16 slides in a longer longitudinal slot 17&#39;&#34; the drug dose is larger. 
     The adaptation of the drug dose to the requirements of the patient is performed solely by the doctor who can release the locking ring 9 of the device by means of a special key which engages a recess 26 of locking ring 9 and loosen it until the cam follower 16 of the dispensing mechanism 20 is disengaged from the relevant longitudinal slot 17. The doctor can now select the desired dose by rotating the disengaged dispensing mechanism 20 and re-engaging the cam follower 16 in a shorter or longer longitudinal slot 17. The scale 21 on the dose ring 5 shows the selected setting in the window 18. Once the locking ring 9 is re-tightened by the doctor with the aid of the key the cam follower 16 can only move in a longitudinal direction within the selected longitudinal slot 17. The drug dose to be dispensed is defined solely by the depth of the longitudinal slot 17 working in conjunction with the cam follower 16. 
     If the syringe device according to the invention is operated as specified no further (second) dose can be dispensed from the ampoule 11 even though there may be a sufficient residual supply of the drug in the ampoule 11. The dispensing mechanism 20 is thus set for single-shot dispensing of a fixed dose and cannot be altered by the patient. 
     In order to inject a further dose of the drug, the patient must release the ampoule sleeve 10 from the mechanism holder 1 and discard it together with the ampoule 11. The device can only be re-used once a fresh ampoule 11 has been inserted. 
     So that the patient is not tempted to remove any residual quantity of the drug by some means or other from the ampoule and use it, the housing 25 which accommodates the ampoule 11 is designed such that the ampoule 11 can only be removed from it with extreme difficulty. Furthermore, the housing 25 is preferably made of an optically opaque material, for example polyamide, with the result that any possible residual quantity is not visible. 
     In order to inject a new dose of the drug, the old lower sleeve-like component 10 is simply replaced by a new one. In this way, the patient is unable to establish whether a residual quantity of drug is left in the ampoule 11 and, if so, how much. This is of particular significance when preservative-free Papaverin is used which, if an overdose were to be taken, would result in irreparable damage.