Medical delivery system

[0001] This application claims the benefit of priority under 35 USC 119 of U.S. Provisional Application Serial No. 60/343,052, filed Dec. 22, 2001 and Danish Application PA 2001 01814, filed Dec. 6, 2001; the contents of both are hereby incorporated by reference.

[0002] The invention relates to a medication delivery device for delivering medicine or other fluent material into a mammal body, and especially to a medication delivery device where a plunger located in a tubular cartridge is connected to a plunger rod.

[0003] Medication delivery devices are widely used throughout the health sector for delivering fluent medicine into mammal bodies through a conduit inserted in the body. In general two types of medication delivery devices exist. The first type being an injection device, which injects a predetermined dose of the fluent medicine into a mammal body whenever the injection device is activated. The other type being an infusion device, which delivers a constant rate of medicine into a mammal body either by gravity or by pressure, which pressure are usually generated by an electrical motor.

[0004] The fluent medicine is usually contained in a cartridge, which can be either a fillable cartridge or a pre-filled disposable cartridge. Such known cartridges are e.g. provided as a cylindrical barrel having a penetrable membrane at a distal end and a movable plunger at the opposite proximal end. A conduit penetrating the membrane is mounted at the distal end.

[0005] When the plunger is moved towards the membrane the fluent medicament contained in the cartridge is pressed out through the conduit. When the conduit is mounted it is however possible for the medicament to escape out through the conduit and for the plunger to move towards the distal end only by the influence of gravity. In delivery systems such as pump systems, where the conduit is in contact with the fluid medicament for a substantial period of time, it is normal procedure to connect the plunger to the plunger rod in order to provide a controlled forward movement of the plunger thereby preventing the cartridge from emptying itself.

[0006] Some infusions pumps available today have a fillable cartridge, which are filled with the medicament prior to use. Such fillable cartridge usually has a plunger having the back wall provided with an interior thread into which a pull rod is screwed. The plunger can then be moved backwards inside the fillable cartridge, and the cartridge can be filled with medicine from a vial. Once the reusable cartridge has been filled, the plunger is disconnected from the pull rod and connected to the pump plunger rod. The assembled cartridge and plunger rod are then inserted into the infusion pump.

[0007] It is however desirable to use pre-filled cartridges in pump systems. A major problem in fulfilling this desire is to obtain a suitable connection between the plunger rod of the pump system and the plunger of such pre-filled cartridge.

[0008] Different ways of connecting a plunger in a pre-filled cartridge with a plunger rod is disclosed in WO 98.11927.

[0009] If the plunger rod is not located at the centre of the plunger, the plunger might tilt once the plunger rod is connected with the plunger rod. When the plunger tilts the sealing between the cartridge wall and the plunger will become leaky.

[0010] One way of preventing tilting is, as also disclosed in WO 98/11927, by providing an auxiliary part such as Velcro tape, a magnet or a ball and socket connection at the centre of the plunger. This will ensure that the plunger rod will always connect the plunger at the centre. It is however rather cumbersome from a manufactures point of view and will give rise to a number of failures if the auxiliary part has been disconnected from the plunger prior to use.

[0011] When using pre-filled cartridges, it would be preferred if the same pre-filled cartridge can be used both for pump systems and for traditional pen syringes. In pen syringes there are however no connection between the plunger and the plunger rod. Usually the plunger rod has a somewhat flat end, which abuts the plunger. If auxiliary parts are permanently mounted on the plunger, it will be impossible to use the cartridge in an ordinary pen syringe.

[0012] An infusion system into which a pre-filled syringe is mounted is disclosed in U.S. Pat. No. 5,928,202. The plunger rod shown in this system is at the distal end provided with a ball-shaped portion and the plunger is provided with a spherical cavity into which the ball-shaped portion can be loaded. The channel of the pre-filled syringe has at the proximal end a funnel-shaped part, which closes the cavity of the plunger around the ball-shaped portion of the plunger rod as the plunger rod is advanced forward. The presence of the funnel-shaped part makes it impracticable to use this solution for a glass cartridge, since these are normally produced with a constant inside diameter, thus it is generally considered an inconvenience to have an uneven outer diameter on a cartridge. The design disclosed in U.S. Pat. No. 5,928,202 does not allow plunger rod disconnection when the plunger is located outside the funnel-shaped zone, and the size of the disconnection force is depended on the exact position of the plunger in the funnel-shaped zone.

[0013] In ordinary syringes the plunger is drawn backwards both when the medicament is drawn into the syringe from a vial, and when the injection is being performed to ensure that the needle has not struck a blood vessel. It is therefore a major concern for these types of syringes to ensure that the connection between the plunger and the plunger rod is permanent. Such a connection involving a ball and socket connection which cannot be disconnected is disclosed in EP 395.211, FIG. 12.

[0014] If a ball-shaped portion of a plunger rod is pressed into an interior spherical cavity in a plunger through a circular orifice having a diameter smaller than the diameter of the ball-shaped portion it will be very difficult to disconnect the two parts, and such a connection would henceforth be characterized as permanent.

[0015] It is an object of the present invention to provide a disconnectable ball and socket connection which can be used for pre-filled cartridges of the types having a constant inside diameter and which pre-filled cartridges can be used both in pump systems and in ordinary pen type injection systems.

[0016] In order to overcome the drawbacks of the prior art it is herein suggested to provide the plunger with an interior cavity engaged by a spherical or semi spherical portion of the plunger rod. According to claim 1 the spherical shaped portion is provided with indentations.

[0017] By providing the ball-shaped portion with a number of suitable indentations it has surprisingly been found that the connection can be connected and disconnected using only a limited amount of force, because the indentations allow air in the plunger cavity to escape during plunger rod connection thereby avoiding a counteract pressure build up. The same situation occurs during disconnection as air need to pass through the indentations to avoid counteract under pressure i.e. vacuum in the plunger cavity.

[0018] If the diameter of a circular orifice or the minimum cross section of a non-circular orifice has the same diameter as the spherical or semi spherical shaped portion of the plunger rod, a connection, which is very easy to disconnect, is obtained. If however the diameter of the spherical or semi spherical shaped portion of the plunger rod is larger than the minimum cross section or diameter of the open orifice of the plunger as specified in claim 2, the connection will be somewhat tighter.

[0019] A suitable disconnectable grip is possible if the outside diameter of the spherical or semi spherical shaped end portion of the plunger rod and the inside diameter of the interior cavity is approximately between 3 to 7 mm and preferably around 5 to 6 mm for a cartridge of 9 to 11 mm, while the diameter of the open orifice should be approximately between 3.5 to 7, mm, preferably around 4 to 5 mm.

[0020] The indentations are preferably made such that the spherical or semi spherical shaped portion of the plunger rod has a cross-shaped cross section perpendicular to the longitudinal axis of the plunger rod, as disclosed in claim 3. This provides a suitable connection between the plunger rod and the plunger, where the force needed to disconnect the two parts are determined by the width of the arms of the cross in combination with the diameter of the cross and of the open orifice.

[0021] Since bulging of a flexible plunger gives rise to either back suction or after drip when the plunger returns to its initiate form after it has been compressed, bulging should be avoided. In order to minimize bulging of the plunger, which is preferably made from a resilient material such as an elastomeric rubber composition, the point of contact between the plunger rod and the plunger should be located as close to the front wall of the plunger as possible.

[0022] It has also been fund that the plunger rod is easier guided into the open orifice if the most distal end of the plunger rod has the shape of a spherical cap such as indicated in claim 4.

[0023] Instead of providing the spherical or semi spherical shaped portion of the plunger rod with indentations, the open orifice can be made circular with protrusions, as specified in claim 6. This will also allow air to escape from the cavity during connection, and air to pass into the cavity during disconnection.

[0024] When as disclosed in claim 7, the circular cross section of the open orifice has a diameter substantially equal to or larger than the diameter of the spherical or semi spherical shaped portion of the plunger rod and the cross section formed between the protrusions are smaller than the diameter of the spherical or semi spherical shaped portion of the plunger rod it is ensured that the connection is easy disconnectable.

[0025] The open orifice could also be provided with a non-circular cross section as specified in claim 9, as this will also allow air to escape from the cavity during connection, and air to pass into the cavity during disconnection.

[0026] In order to obtain a good grip, the minimum cross section of the open non-circular orifice should be substantially the same or smaller than the diameter of the spherical or semi spherical portion of the plunger rod, such as cited in claim 10.

[0027] The connection between the plunger and the plunger rod as such is claimed in claim 5, 8 and 11.

[0028] Definitions

[0029] In the present context, the term semi spherical is used to describe an object such as a cavity or an end portion of a plunger having a three-dimensional geometry where at least a part of the surfaces has the shape of a spherical cap.

[0030] The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

[0031] FIGS. 1 to 5 Show a sectional view of a plunger according to an embodiment of the invention.

[0032] FIG. 6 Show a sectional view of a plunger according to an embodiment of the invention having protrusions.

[0033] FIGS. 7 to 12 Show a top view of a plunger according to an embodiment of the invention.

[0034] FIG. 13 Show a sectional view of a plunger rod according to an embodiment of the invention

[0035] FIG. 14 Show a sectional view of a plunger rod according to an embodiment of the invention having a cross-shaped end portion.

[0036] FIGS. 15 to 18 Show a sectional view of a plunger rod according to an embodiment of the invention having different forms of apertures.

[0037] FIGS. 19-20 Show a sectional view of a plunger rod according to an embodiment of the invention having outwardly pointing protrusions.

[0038] FIG. 21 Show a sectional view of a plunger rod according to an embodiment of the invention having slots.

[0039] The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

[0040] Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.

[0041] Initially it may be convenient to define that the term distal end is meant to refer to the end of cartridge where the fluid medicament is contained and where the conduit is inserted, whereas the term proximal end is meant to refer to the opposite end where the plunger is located in its initial position.

[0042] FIGS. 1-6 shows different embodiments of a plunger 1 as seen from the side.

[0043] The plunger 1 illustrated in FIG. 1 has a front wall 2, which is in contact with the fluid medicament inside the cartridge and an opposite located back wall 3. Encapsulated in the interior of the plunger 1 is a spherical cavity 4 provided. This cavity 4 is connected to the back wall 3 through an open orifice 5.

[0044] In the embodiment disclosed in FIG. 2, the cavity 4 is prolonged in the distal direction with an additional cylindrical appendix 6.

[0045] The cavity 4 shown in FIG. 3 has only a semi spherical shape, as the proximal end 7 of the cavity 4 has the shape of a spherical cap, while the distal end of the cavity has a cylindrical form.

[0046] FIG. 4 also shows a semi spherical cavity 4 having the shape of a spherical cap at the distal end 8, while the proximal end has a cylindrical shape. The proximal end of the open orifice 5 could be provided with an inlet 22, which makes it easier to load the plunger rod 6 into the open orifice 5.

[0047] The plunger illustrated in FIG. 5 has a cavity 4 similar to the cavity 4 shown in FIG. 4, however the open orifice has a diameter equal to the diameter of both the cylindrical part and the spherical cap part.

[0048] In order to enhance the grip between the plunger 1 and the plunger rod 6 in the embodiment shown in FIG. 5, the open orifice 5 could be provided with protrusions 9 as illustrated in FIG. 6. The number and size of the protrusions 9 can be chosen randomly in order to provide the grip needed for a particular injection or infusion system.

[0049] FIG. 7 shows a top view of a plunger with two such protrusions 9, and FIG. 8 shows a plunger with four protrusions 9.

[0050] The open orifice 5 could have a substantially circular cross section 10 as shown in FIG. 9, or the cross section could be four-sided 11 as shown in FIG. 10 and FIG. 11. The non-circular cross section of the open orifice 5 could in fact be any kind of polygon 12 as indicated in FIG. 12, or even any other shape e.g. shaped like a four-leaf.

[0051] The plunger rod 6 of the connection is shown in FIGS. 13-20. When the spherical or semi spherical end portion 13 of the plunger rod 6 is inserted into the cavity 4 of the plunger 1 a hipbone connection is established. Due to this hipbone connection a plunger rod 6 with a diameter substantially smaller than the diameter of the cartridge can be used without tilting the plunger 1 if the plunger rod 6 is pressed towards the side of the cartridge. When the plunger 1 and the plunger rod 13 are connected in a stiff or permanent connection, the plunger might tilt and cause leakage if the plunger rod 13 is not kept in the centre of the cartridge, a hipbone connection however solves this problem.

[0052] FIG. 13 illustrates a plunger rod 6 with a spherical shaped end portion 13 located at the distal end of the plunger rod 6. In order to obtain a disconnectable connection this spherical shaped portion 13 is preferably provided with tracks, slots, apertures or similar indentations as illustrated in FIGS. 14-18.

[0053] In the embodiment disclosed in FIG. 14, the spherical shaped end portion 13 of the plunger rod 6 has a cross-shaped cross section when viewed perpendicular to the longitudinal axis of the plunger rod 6. The cross 14 has four arms, which arms each abuts the imaginary diameter of the spherical end portion 13. The space 15 between the arms can off cause vary in size, which is also the case for the number of arms. Both FIG. 14 and FIG. 14a shows a schematic view of the cross section of the spherical part 13.

[0054] The space 15 needs not extend through the full longitudinal diameter of the spherical shaped portion 13, but could end at a line 16 leaving a spherical cap 17 at the most distal end of the spherical end portion 13, as shown in FIG. 14a.

[0055] A number of different plunger rods 6 are disclosed in FIGS. 15-17. These plunger rods 6 has a spherical portion 13 at the distal end with indentations 18. These indentations all leave a spherical cap 17 at the most distal end of the plunger rod 6.

[0056] FIG. 18 shows a plunger rod 6 where the spherical portion 13 is provided with indentations leaving a spherical cap 17 at the proximal end of the spherical end portion 13

[0057] The distal end of the plunger rod 6 could also, as shown in FIG. 19, be provided with a semi spherical end portion 19 which could be provided with outwardly pointing protrusions 20 in order to enhance the grip. Such protrusions 20 could also be provided at the spherical end portion 13 of the plunger rod 6 as shown in FIG. 20.

[0058] FIG. 21 shows a plunger rod 6 with a spherical end portion 13 having two slots 21. A schematic view of the cross section of the spherical part 13 is also included.

[0059] Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.