Device for delivering medicament encompassing a pressure release mechanism

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.

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'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 claim1. 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.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a non-limiting example of a medicament delivery device where the present invention could be utilized. The delivery device comprises a housing10designed 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 inFIG. 2, inside and at the front end of the housing a medicament containing container12is arranged having a front end onto which an opening14e.g. a needle, may be attached. Said medicament delivery device comprises pressure means including a movable wall part16, hereafter called stopper, arranged inside the container; and a pressure member18as 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 member42and a driver26.

The Delivery Device of the Present Invention According to a First Embodiment

FIGS. 1,2,3a,3brefer to a configuration of the delivery device wherein the pressure release means comprises a nut20having a first mating member24arranged and designed to interact with a second mating member70. 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 member70.

Said nut20has a through-going central bore22having corresponding threads as the plunger rod, and two outwardly protruding pivoting pins23slidable journalled in the housing. As shown inFIGS. 3aand3b, the upper surface of the nut, facing towards the rear end of the delivery device, is arranged with the first mating member24designed and arranged as a number of indentations having a ratchet form, hereafter called the indentations24. The function of the indentations will be described in detail below.

The driver26,FIG. 2, is further arranged around the plunger rod. The driver has a lower, cylindrical front portion28having a number of outwardly directed protrusions30evenly spaced around its circumference where the distance between two adjacent protrusions constitutes a certain predetermined dose quantity, and a second elongated cylindrical portion32. In the transition between the first and the second portion, two outwardly directed ledges34are 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 member70designed and arranged as indentations, hereafter called the indentations70, that cooperate with the indentations24of the nut20as a pressure release mechanism that will be described below.

Surrounding the second portion32of the driver26is a drive wheel36of a generally cylindrical shape. The outer surface of the drive wheel is arranged with a number of evenly spaced outwardly directed protrusions38having the same increment distance as the protrusions of the driver. The drive wheel is further arranged with a central through-going bore40having a diameter slightly larger than the second portion of the driver. The through-going bore is further arranged with cut-outs41to accommodate the ledges34of the driver26, but somewhat larger, corresponding to the increment distance of the protrusions, as will be described below, to enable a certain rotational movement between the driver26and the drive wheel36.

Further the energy accumulating member42e.g. a flat spring, is wound around the second portion of the driver having its inner end attached to the driver26. A tensioning knob44is arranged at the rear end of the delivery device, to which the outer end of the spring42is attached. An activation mechanism46is also arranged on the delivery device. It comprises a button48protruding through a hole in the housing. The button is attached to a fork-like section having two arms50on either side of the container and plunger rod. Two outwardly protruding pivoting pins54are 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 ring56is attached. The inner side of the ring is arranged with oppositely placed, inwardly directed ledges58. The ledges are positioned 90° in relation to the pivoting pins54.

The device is intended to function as follows. The needle14is attached to the front end of the device and the container by suitable means and a needle sheath is removed. The tensioning knob44is then turned whereby the spring42is tensioned. The driver is prevented from turning due to that at least one of the ledges58of the ring56of the activator is in contact with one of the protrusions30of the driver.

When an injection is to be performed, the needle is penetrated on a suitable location on the skin, and the button48is activated by a backwardly axial movement. The activation of the button causes the ledge58of the activator to move out of contact with the protrusion30of the driver, whereby the driver is free to rotate. Further, the movement of the activation mechanism causes the opposite ledge58to move in contact with the protrusions38of the drive wheel36, thereby locking the drive wheel from rotation.

The rotation of the driver26causes the plunger rod18to rotate and causes also its indentations70to cooperate with the indentations24of the nut20. Due to the threaded engagement between the plunger rod and the nut20and the indentations cooperation, the plunger rod moves axially; first forwardly pushing on the stopper16whereby 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 ledge34of the driver26comes in contact with a side wall of the cut-outs41of the drive wheel36, 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 button48is released, the slidable and resilient pivoting pins54causes the activation mechanism and thereby one of the ledges58to again come in contact with a protrusion30of the driver, at the same time as the ledge58previously holding the drive wheel36moves out of contact with the protrusions38of 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. 1,2,4a,4brefer to a configuration of the delivery device, wherein the pressure release means comprises a nut20′ having a first mating member24′ which is arranged and designed to interact with a second mating member70′ of a ring60. Said ring60is fixedly attached to the inner surface of the housing, and has further a through-going central bore.

As shown inFIGS. 4aand4b, the upper surface of the ring60, facing towards the proximal end of the delivery device, is arranged with the second mating member70′ arranged and designed as a number of indentations, hereafter called the indentations70′, having a kind of wavy form “valleys”. The function of the indentations70′ will be described in detail below.

The first mating member24′ of the nut20′ is arranged and designed as a number of small wheels, hereafter called the wheels24′. As shown inFIGS. 4aand4b, the upper surface of the nut20′, facing towards the distal end of the delivery device, has an elongated cylindrical portion25arranged around the plunger rod and having corresponding threads as the plunger rod. Further, said elongated cylindrical portion25passes through the through-going central bore of the ring60in order to be rotationally connected to the driver26(not shown).

At the start of an injection, the wheels24′ are placed in the “valleys” of the ring60. Thereafter, the rotation of the driver26causes both the plunger rod18′ and the nut20′ to rotate wherein the wheels24′ are moved out of the indentations70′ or “valleys” and at the end of the injection, the wheels24′ will move into the next valley. This forwardly and backwardly axial movement of the nut20′ will cause a pressure release on the plunger rod18′ and thereby on the stopper16and on thus the content of the container.

Alternative Activation Mechanism

InFIG. 5is shown a distal part of the medicament delivery device comprising a tensioning knob44′ connected to an energy accumulating member42′ in the form of a flat spiral spring and a threaded plunger rod18′. Said medicament delivery device shown inFIG. 5shows also a driver26′, a coupling member80and a coupling spring82, wherein said coupling member further comprising a crown84with beveled protrusions86. The driver26′ is provided with a skirt88and beveled recesses90as well as a non-rotating bearing92, provided with an interior tubular formed part (not shown).

The exterior of the proximal part of the driver26′ is provided with a number of dose step protrusions30′, equally distributed along the circumference of the proximal part of the driver26′. Every other protrusion30′ais however provided a predetermined distance distal to the rest of the protrusions30′b. The protrusions30′aare thus provided equally distributed along the circumference of the driver26′ with their centers provided a certain distance from the proximal end of the driver26′, and the protrusions30′bare thus also provided equally distributed along the circumference of the driver26′ but with their centers provided a shorter distance from the proximal end of the driver26′ than the protrusions30′a. The distance between the centers of every protrusion30′ along the circumference of the driver26′ 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 mechanism46′ of the delivery device according toFIG. 5is provided with a slidable arm48′ provided with an inwardly protruding stopper means96adapted to set the driver26′ in a non-rotating state as well as a rotating state. The activation mechanism46′, and thus also the stopper means96, 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 protrusions30′aand30′bin the longitudinal direction. That is, when the stopper means96abuts against, as seen inFIG. 5, the right hand side of a protrusion30′, the driver26′ 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 knob44′ 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 protrusion30′aprovided closer to the distal end of the driver26′ than the protrusions30′b, the user then moves the activation mechanism46and thus also the stopper means96, the predetermined distance towards the proximal end of the device, whereby the stopper means96releases the plunger rod driver26′ for rotation which sets the device in a medicament delivery state. If the stopper means96on the other hand abuts against a protrusion30′b, the user then instead moves the activation mechanism46′ and thus also the stopper means96, the predetermined distance towards the distal end of the device, whereby the stopper means96releases the driver26′ for rotation.

When the driver26′ is free to rotate, the output torque provided by the spring42′ will rotate the driver26′ and hence also the rod18′. However, independent of the energy accumulated in the spring42′, the driver26′ will only rotate until the stopper means96abuts against the protrusion30′ following the protrusion30′ it previously abutted against in the direction along the circumference of the driver26′, whereby the stopper means96travels along the circumferential surface of the driver26′ the predetermined distance between the two protrusions30′aand30′bin the direction along the circumference of the driver26′, each time the driver is rotated.

That is, if the stopper means96initially abuts against the right hand side of the protrusion referred to as30′ainFIG. 5, the stopper means96will after the one step counter clockwise rotation of the driver26′, abut against the protrusion referred to as30′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 driver26′ 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 protrusion30′aand a protrusion30′bin the direction along the circumference of the driver26′, 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 driver26′ with protrusions30′, 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.