Abstract:
The present invention relates to a device for delivering medicament, comprising a container ( 12 ) arranged to contain medicament, which container further comprises an opening arranged to expel medicament from the container, pressure means ( 16, 18 ) arranged to exert pressure on the medicament inside the container ( 12 ) for expelling a certain predetermined quantity of the medicament through the opening, driving means ( 26, 42 ) for driving said pressure means ( 16, 18 ), and activation means ( 46 ) for activating said driving means ( 26, 42 ) wherein said device comprises pressure release means ( 20 ) which are adapted, arranged and designed such that, when the predetermined dose has been expelled through the opening, the pressure on the medicament is released.

Description:
TECHNICAL FIELD 
     The present invention relates to a pressure release mechanism, and in particular in connection with medicament containing devices where the medicament is in a container and is exposed to pressure when the medicament is to be delivered. 
     BACKGROUND ART 
     There are numerous devices for delivering medicament on the market and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. A very common design is a generally tubular compartment having a stopper in one end of the compartment and a needle unit attached to the opposite end of the compartment. 
     In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a pusher rod, which could be done manually by a finger of a physician or trained person, which is the case for simple handheld syringes, or by pressure means such as springs or compressed air cartridges, which is common in automatic or semi-automatic injectors. 
     In many instances it is desirable to be able to deliver a certain specified quantity of the medicament. This is for example the case with a multi-dose injection device, which is capable of delivering a number of specified, set, doses until the compartment is empty. One example is disclosed in the European patent application No. 05104734.8 where specific doses can be set before injection. The injection device disclosed is arranged with spring means for exerting a pressure on the medicament for delivering a specific dose, i.e. pushing the plunger rod and thus the stopper into the container. The delivery of a dose requires a certain force from the spring means in order to overcome the friction between the somewhat resilient stopper and the inner surface of the container and also to be able to press the medicament in liquid form through a rather small passage in the needle, possibly within a predetermined time. 
     Due to the elasticity of the components under pressure such as the stopper and also the medicament of non-newtonian, there is a prevailing pressure even when the stopper has been moved a predetermined distance and the dose has been delivered. This is in particular pronounced when handling medicament with rather high viscosity, medicament having resilient properties. 
     With this type of substance with high viscosity, and because very small needles are often used, a rather large force is required and because of the elasticity of the components, often a certain small quantity of the substance comes out of the needle even after performed injection when the pressure is released, i.e. there is some dripping from the needle, which is unwanted, in particular when treating a patient and the substance may be dripping on the patient&#39;s skin, possibly causing irritation or inconvenient, undesirable effects. 
     The above mentioned gel-based substances are typically injected manually, i.e. a normal type of syringe is used. Because of the rather large forces required for injecting the substances, and also due to the many small injections needed for a treatment, it is tiresome for the operator to use such a syringe during a treatment. 
     There are thus a number of aspects that are addressed with the present invention. 
     DISCLOSURE OF INVENTION 
     The aim of the present invention is to remedy a number of drawbacks and problems associated with the state of the art devices of the above mentioned type and to provide improvements that facilitate the handling of medical devices. 
     This aim is achieved with a device according to claim  1 . Preferable embodiments of the present invention are subject of the dependent claims. 
     According to a main aspect of the present invention it is characterized by a device for delivering medicament comprising a housing; a container arranged to contain medicament, which container further comprises an opening arranged to expel medicament from the container; pressure means comprising a movable wall part within said container and a pressure member arranged to exert pressure on the medicament inside the container for expelling a certain predetermined quantity of the medicament through the opening; driving means for driving said pressure means; and activation means for activating said driving means wherein said device further comprises pressure release means for releasing the pressure on the medicament after the predetermined dose has been expelled through the opening. 
     According to another aspect of the invention, said pressure member is arranged to interact with said driving means for moving said movable wall part forwardly and thereby expelling a certain predetermined quantity of the medicament through the opening, and wherein said pressure member is also arranged to interact with said pressure release means for moving said pressure member slightly backwards after the predetermined dose has been expelled through the opening. 
     The advantages with the present invention are several. The pressure release means ascertains that the residual pressure in the components of the device after delivery of medicament is relieved, which thereby prevents any medicament from being expelled after injection, i.e. preventing drooling of the device. 
     Many devices comprise pressure means in the form of a plunger rod activated by spring means, which plunger rod moves axially into the compartment of the medicament and the present invention enables the pressure on the plunger rod to be released due to a short axial movement backwards at the end of the injection. With this reliable mechanical solution, no surplus medicament is expelled after injection, which is a particular problem with medicament having a high viscosity or even gel-like properties. However the drooling phenomenon is not limited to such substances but is as relevant for medicament with lower viscosity. 
     These and other aspects of and advantages with the present invention will become apparent from the following detailed description of the invention and from the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the following detailed description of the invention, reference will be made to the accompanying drawings, of which 
         FIG. 1  shows an example of an injection device according to the present invention, 
         FIG. 2  is an exploded view of the injection device according to  FIG. 1 , 
         FIG. 3   a, b  show one embodiment of a pressure release mechanism according to the invention, 
         FIG. 4   a, b  show another embodiment of a pressure release mechanism according to the invention, and 
         FIG. 5  shows an alternative embodiment of an activation mechanism for the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a non-limiting example of a medicament delivery device where the present invention could be utilized. The delivery device comprises a housing  10  designed to be held in one hand for delivering repeated small quantities of medicament step by step. It is however understood that other types of delivery devices may have the pressure release mechanism to be described in detail below. 
     As seen in  FIG. 2 , inside and at the front end of the housing a medicament containing container  12  is arranged having a front end onto which an opening  14  e.g. a needle, may be attached. Said medicament delivery device comprises pressure means including a movable wall part  16 , hereafter called stopper, arranged inside the container; and a pressure member  18  as a threaded plunger rod, arranged to push on the stopper. The front end of the plunger rod is preferably pointed to minimize the friction between the plunger rod and the stopper. Said medicament delivery device also comprises driving means including an energy accumulating member  42  and a driver  26 . 
     The Delivery Device of the Present Invention According to a First Embodiment 
       FIGS. 1 ,  2 ,  3   a ,  3   b  refer to a configuration of the delivery device wherein the pressure release means comprises a nut  20  having a first mating member  24  arranged and designed to interact with a second mating member  70 . Said nut is adapted to be in a non-rotating state but having a forwardly and a backwardly axial movement during medicament delivery due to the interaction with the second mating member  70 . 
     Said nut  20  has a through-going central bore  22  having corresponding threads as the plunger rod, and two outwardly protruding pivoting pins  23  slidable journalled in the housing. As shown in  FIGS. 3   a  and  3   b , the upper surface of the nut, facing towards the rear end of the delivery device, is arranged with the first mating member  24  designed and arranged as a number of indentations having a ratchet form, hereafter called the indentations  24 . The function of the indentations will be described in detail below. 
     The driver  26 ,  FIG. 2 , is further arranged around the plunger rod. The driver has a lower, cylindrical front portion  28  having a number of outwardly directed protrusions  30  evenly spaced around its circumference where the distance between two adjacent protrusions constitutes a certain predetermined dose quantity, and a second elongated cylindrical portion  32 . In the transition between the first and the second portion, two outwardly directed ledges  34  are arranged on opposite sides of the driver. The driver is hollow to accommodate the plunger rod in a rotationally locked position. The front surface of the driver, i.e. facing the front end of the delivery device, is designed to have the second mating member  70  designed and arranged as indentations, hereafter called the indentations  70 , that cooperate with the indentations  24  of the nut  20  as a pressure release mechanism that will be described below. 
     Surrounding the second portion  32  of the driver  26  is a drive wheel  36  of a generally cylindrical shape. The outer surface of the drive wheel is arranged with a number of evenly spaced outwardly directed protrusions  38  having the same increment distance as the protrusions of the driver. The drive wheel is further arranged with a central through-going bore  40  having a diameter slightly larger than the second portion of the driver. The through-going bore is further arranged with cut-outs  41  to accommodate the ledges  34  of the driver  26 , but somewhat larger, corresponding to the increment distance of the protrusions, as will be described below, to enable a certain rotational movement between the driver  26  and the drive wheel  36 . 
     Further the energy accumulating member  42  e.g. a flat spring, is wound around the second portion of the driver having its inner end attached to the driver  26 . A tensioning knob  44  is arranged at the rear end of the delivery device, to which the outer end of the spring  42  is attached. An activation mechanism  46  is also arranged on the delivery device. It comprises a button  48  protruding through a hole in the housing. The button is attached to a fork-like section having two arms  50  on either side of the container and plunger rod. Two outwardly protruding pivoting pins  54  are arranged on each of the arms, which pivoting pins are slidable and resilient journalled in the housing. On the rear end of the arms, a ring  56  is attached. The inner side of the ring is arranged with oppositely placed, inwardly directed ledges  58 . The ledges are positioned 90° in relation to the pivoting pins  54 . 
     The device is intended to function as follows. The needle  14  is attached to the front end of the device and the container by suitable means and a needle sheath is removed. The tensioning knob  44  is then turned whereby the spring  42  is tensioned. The driver is prevented from turning due to that at least one of the ledges  58  of the ring  56  of the activator is in contact with one of the protrusions  30  of the driver. 
     When an injection is to be performed, the needle is penetrated on a suitable location on the skin, and the button  48  is activated by a backwardly axial movement. The activation of the button causes the ledge  58  of the activator to move out of contact with the protrusion  30  of the driver, whereby the driver is free to rotate. Further, the movement of the activation mechanism causes the opposite ledge  58  to move in contact with the protrusions  38  of the drive wheel  36 , thereby locking the drive wheel from rotation. 
     The rotation of the driver  26  causes the plunger rod  18  to rotate and causes also its indentations  70  to cooperate with the indentations  24  of the nut  20 . Due to the threaded engagement between the plunger rod and the nut  20  and the indentations cooperation, the plunger rod moves axially; first forwardly pushing on the stopper  16  whereby the medicament is expelled through the needle and thereafter backwardly to obtain a pressure release on the plunger and thereby on the stopper and on thus the content of the container. 
     When the driver has rotated a certain increment distance the ledge  34  of the driver  26  comes in contact with a side wall of the cut-outs  41  of the drive wheel  36 , and because the drive wheel is locked, the movement of the driver is stopped. In this it is to be understood that the distance between the protrusions of the driver, together with the pitch of the thread of the plunger rod constitutes a certain predetermined dose quantity. I.e. in order to set a specific dose, which is done during manufacture of the device, a certain distance is chosen between the protrusions as well as a certain pitch of the threads of the plunger rod. 
     When the button  48  is released, the slidable and resilient pivoting pins  54  causes the activation mechanism and thereby one of the ledges  58  to again come in contact with a protrusion  30  of the driver, at the same time as the ledge  58  previously holding the drive wheel  36  moves out of contact with the protrusions  38  of the drive wheel, whereby it is released. A small spring, not shown, is arranged between the driver and the drive wheel to move the drive wheel back to the original position in relation to the driver. The injector is now ready for a subsequent injection. 
     The Delivery Device of the Present Invention According to a Second Embodiment 
       FIGS. 1 ,  2 ,  4   a ,  4   b  refer to a configuration of the delivery device, wherein the pressure release means comprises a nut  20 ′ having a first mating member  24 ′ which is arranged and designed to interact with a second mating member  70 ′ of a ring  60 . Said ring  60  is fixedly attached to the inner surface of the housing, and has further a through-going central bore. 
     As shown in  FIGS. 4   a  and  4   b , the upper surface of the ring  60 , facing towards the proximal end of the delivery device, is arranged with the second mating member  70 ′ arranged and designed as a number of indentations, hereafter called the indentations  70 ′, having a kind of wavy form “valleys”. The function of the indentations  70 ′ will be described in detail below. 
     The first mating member  24 ′ of the nut  20 ′ is arranged and designed as a number of small wheels, hereafter called the wheels  24 ′. As shown in  FIGS. 4   a  and  4   b , the upper surface of the nut  20 ′, facing towards the distal end of the delivery device, has an elongated cylindrical portion  25  arranged around the plunger rod and having corresponding threads as the plunger rod. Further, said elongated cylindrical portion  25  passes through the through-going central bore of the ring  60  in order to be rotationally connected to the driver  26  (not shown). 
     At the start of an injection, the wheels  24 ′ are placed in the “valleys” of the ring  60 . Thereafter, the rotation of the driver  26  causes both the plunger rod  18 ′ and the nut  20 ′ to rotate wherein the wheels  24 ′ are moved out of the indentations  70 ′ or “valleys” and at the end of the injection, the wheels  24 ′ will move into the next valley. This forwardly and backwardly axial movement of the nut  20 ′ will cause a pressure release on the plunger rod  18 ′ and thereby on the stopper  16  and on thus the content of the container. 
     Alternative Activation Mechanism 
     In  FIG. 5  is shown a distal part of the medicament delivery device comprising a tensioning knob  44 ′ connected to an energy accumulating member  42 ′ in the form of a flat spiral spring and a threaded plunger rod  18 ′. Said medicament delivery device shown in  FIG. 5  shows also a driver  26 ′, a coupling member  80  and a coupling spring  82 , wherein said coupling member further comprising a crown  84  with beveled protrusions  86 . The driver  26 ′ is provided with a skirt  88  and beveled recesses  90  as well as a non-rotating bearing  92 , provided with an interior tubular formed part (not shown). 
     The exterior of the proximal part of the driver  26 ′ is provided with a number of dose step protrusions  30 ′, equally distributed along the circumference of the proximal part of the driver  26 ′. Every other protrusion  30 ′ a  is however provided a predetermined distance distal to the rest of the protrusions  30 ′ b . The protrusions  30 ′ a  are thus provided equally distributed along the circumference of the driver  26 ′ with their centers provided a certain distance from the proximal end of the driver  26 ′, and the protrusions  30 ′ b  are thus also provided equally distributed along the circumference of the driver  26 ′ but with their centers provided a shorter distance from the proximal end of the driver  26 ′ than the protrusions  30 ′ a . The distance between the centers of every protrusion  30 ′ along the circumference of the driver  26 ′ is however equal if, as in this case, the predetermined dose steps are to be equally large, i.e. every dose step delivers the same predetermined amount of medicament. 
     An activation mechanism  46 ′ of the delivery device according to  FIG. 5  is provided with a slidable arm  48 ′ provided with an inwardly protruding stopper means  96  adapted to set the driver  26 ′ in a non-rotating state as well as a rotating state. The activation mechanism  46 ′, and thus also the stopper means  96 , is therefore adapted to be moved in the longitudinal direction of the device with a distance that corresponds to the distance between the centers of the protrusions  30 ′ a  and  30 ′ b  in the longitudinal direction. That is, when the stopper means  96  abuts against, as seen in  FIG. 5 , the right hand side of a protrusion  30 ′, the driver  26 ′ is prevented to be rotated counterclockwise, i.e. the device is thus in a non-medicament delivery state. 
     When the delivery device is adapted to be used, the user rotates the tensioning knob  44 ′ clock-wise, preferably the maximum number of steps whereby the spiral spring thus winds up and accumulates the largest permitted energy. If the stopper means abut against a protrusion  30 ′ a  provided closer to the distal end of the driver  26 ′ than the protrusions  30 ′ b , the user then moves the activation mechanism  46  and thus also the stopper means  96 , the predetermined distance towards the proximal end of the device, whereby the stopper means  96  releases the plunger rod driver  26 ′ for rotation which sets the device in a medicament delivery state. If the stopper means  96  on the other hand abuts against a protrusion  30 ′ b , the user then instead moves the activation mechanism  46 ′ and thus also the stopper means  96 , the predetermined distance towards the distal end of the device, whereby the stopper means  96  releases the driver  26 ′ for rotation. 
     When the driver  26 ′ is free to rotate, the output torque provided by the spring  42 ′ will rotate the driver  26 ′ and hence also the rod  18 ′. However, independent of the energy accumulated in the spring  42 ′, the driver  26 ′ will only rotate until the stopper means  96  abuts against the protrusion  30 ′ following the protrusion  30 ′ it previously abutted against in the direction along the circumference of the driver  26 ′, whereby the stopper means  96  travels along the circumferential surface of the driver  26 ′ the predetermined distance between the two protrusions  30 ′ a  and  30 ′ b  in the direction along the circumference of the driver  26 ′, each time the driver is rotated. 
     That is, if the stopper means  96  initially abuts against the right hand side of the protrusion referred to as  30 ′ a  in  FIG. 5 , the stopper means  96  will after the one step counter clockwise rotation of the driver  26 ′, abut against the protrusion referred to as  30 ′ b . The next time the user wants to deliver a dose, he then moves the activation mechanism and the stopper means the predetermined distance towards the distal end of the device, whereby the driver  26 ′ rotates another step. This medicament delivery procedure can be repeated until the flat spiral spring has unwound and adapted is original non-energy accumulated state, or until the container is emptied. If the former occurs before the container is emptied, the user may naturally wind up the spiral spring once again. It may be that the manufacturer of the device delivers the device with the spiral spring already in a pre-tensed state, whereby the device should be used as a disposable article, i.e. when the spring has unwound it may not be used any further. The amount of medicament corresponding to one dose step is thus determined by the manufacturer of the device. 
     As mentioned above, the distance between a protrusion  30 ′ a  and a protrusion  30 ′ b  in the direction along the circumference of the driver  26 ′, will determine the amount of medicament to be delivered. If said distance is equal between every protrusion, the amount of medicament will be identical in every dose step. The manufacturer of the device can, however, produce a device comprising a driver  26 ′ with protrusions  30 ′, in which the distance between the protrusions in the direction along the circumference of the member is not equal everywhere. Thus, said distance can vary in correspondence with a predetermined pattern giving rise to a predetermined dose step pattern. For instance, the distance between the protrusions in the direction along the circumference of the driver can become larger and larger, whereupon the amount of medicament delivered will increase for every dose step until the plunger rod driver has completed a full turn. 
     It is to be understood that the embodiments described above and shown on the drawings are to be regarded only as non-limiting examples of the invention and that it can be modified in many ways within the scope of the patent claims.