Patent Description:
As biologic drugs increase in popularity, parenteral delivery devices are expected to be widely used. Injection drug delivery devices, such like the autoinjector, can ease medication preparation/administration and reduce needle injury, which results in improved patient convenience and compliance. Due to the advantages mentioned above, more patients and healthcare professionals prefer automatic injection devices to the traditional manual syringes. Many devices of the above mentioned type allowing a patient to self-administer one or more (generally two) doses of a medicament are known. <CIT> discloses an autoinjector device comprising a syringe housed in a casing formed by an inner part and an outer part capable of sliding in relation to each other. This autoinjector allows a single dose of medicament to be administered. <CIT> discloses a two-dose autoinjector allowing the automatic delivering of a first dose of a medicament and the manual administration of a second dose. An autoinjector of this type is commercially available under the trade mark Twinject® and allows the first dose to be administered automatically, but the second dose must be manually administered. <CIT> describes describes an auto-injector that allows the end-user to self administer first and second doses of a medicament. However, the actuation mechanism for delivering the first and second doses are quite different and the mechanism cannot be applied for delivering more than two doses. <CIT> discloses an injection device allowing the injection of multiple doses through a pushing member having several tooth pitches disposed along its length. <CIT> also discloses a pushing member displacing a syringe piston to dispense an amount of medicament contained in such syringe depending on the position of the tooth pitch engaging the pawls. However, the arming operation of the device disclosed in <CIT> has to be done by manually pulling the device in order to re-arm the injection device. Similarly, <CIT> also fails to disclose an injection device with a re-arming mechanism without manual pulling operation. Another popular type of injection device is a pen injector. Such pen injector devices may contain a dose metering mechanism that administers a dose based on end-user selection. These devices are capable of delivering multiple doses. As for pen injectors, a lead screw or rotating plunger is provided which is mechanically coupled to a dose-setting knob or other actuator through a series of mechanical connections. The typical pen injector mechanism is fairly complex and consists of multiple cooperating parts. The pen injector design mechanism also limits the maximum delivery volume (normally less than <NUM>). For the reasons of cost and simplicity of use, a minimum number of working parts is desired.

It would be an improvement in the art, therefore, to provide a multiple use autoinjector for the automatic injection of a medicament, which is user-friendly and is easier to manufacture as compared to the conventional devices.

The basic idea of the invention is to provide medication delivering mechanisms with features that are typically actuated through direct application of linear force. Dose size is a direct function of advancement of a push rod assembly. Accordingly, it is an aspect of the present invention to provide the push rod assembly for an autoinjector, which may be controllably advanced with a minimum number of cooperating parts.

The present invention provides a reusable, spring-driven autoinjector as defined in claim <NUM>. The autoinjector of the present invention includes a spring-loaded drive mechanism, a trigger mechanism, and a pre-filled medication container. The body of the autoinjector of the present invention includes proximal and distal portions, with the proximal portion housing the drive mechanism and the distal portion housing the medication container. The drive mechanism includes one or more driving springs in association with a push rod assembly. Advantageously, the present invention are achieved by providing a medical injector including the push rod assembly with a plurality of spaced-apart position setting features along the length thereof. The position setting features are configured to allow the push rod to displace distally toward a distal end of the body but not proximally toward a proximal end of the body. The drive mechanism is also capable of being re-armed for multiple times of injection. In addition, the driving mechanism is further provided for controlling the sliding of the medication container from the armed positions to inject the injection needle in an injection site.

Additional and/or other aspects and advantages of the present invention will be set forth in part in the description that follows and, in part, will be apparent from the description, or may be learned by practice of the invention.

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.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
The apparatus presented herein can be used for delivering any of a variety suitable therapeutic agents or substances, such as a drug, into a patient. Initially it may be convenient to define that, the term "distal end" is meant to refer to the end of the automatic medication injection device assembly inserted into the patient, whereas the term "proximal end" is meant to refer to the end opposite to the "distal end" along the longitudinal axis of the device body. The words "upward", "downward", "upper", "lower", "right" and "left" designate directions in the drawings to which reference is made. The words "inward" and "outward" refer to directions toward and away from, respectively, <FIG> illustrate the construction and function mechanism of an exemplary automatic medication injection device assembly <NUM> according to the invention. In this exemplary automatic medication injection device assembly <NUM>, a pre-filled syringe <NUM> is used as medication container. A push cap <NUM>, placed at the proximal end of the device assembly <NUM>, is used to activate an automatic cinjection. The push cap <NUM> is assembled together with an upper cylinder <NUM>. The upper cylinder <NUM> is further assembled with a lower cylinder <NUM>.

There is a separation spring <NUM> between the upper cylinder <NUM> and the lower cylinder <NUM> and landed on a landing feature 103b on the lower cylinder <NUM>. There is an end unit <NUM> placed at the distal end of the device assembly <NUM>. Inside the device assembly <NUM>, there is a push rod assembly. With reference to <FIG>, the push rod assembly includes a push rod sheath <NUM>, a push rod <NUM> and a stopping disk <NUM>. On the push rod <NUM>, there are two pairs of one-way bendable arms 108a and 108b. At the distal end of the push rod <NUM>, there is a push disk feature 108c. At the proximal end of the push rod sheath <NUM>, there are two fingers which are provided with outwardly projecting retaining feature indicated by 107a. At the distal end of the push rod sheath <NUM>, there is a landing feature 107c. A compressed driving spring <NUM> is placed between the landing feature 107c and the upper cylinder <NUM>. Opening feature 107b is provided on the push rod sheath <NUM> for resting the one-way bendable arms 108b. With reference to <FIG>, before use, the end unit <NUM> together with needle shield 111a and needle shield outer 111b on the pre-filled syringe <NUM> are removed. With reference to <FIG>, during the first injection, the push cap <NUM> is pushed distally. The push cap <NUM> is provided with preferably an annular projection, which is arranged to squeeze the retaining feature 107a at the proximal end of push rod sheath <NUM> so that the retaining feature 107a have cleared from the upper cylinder <NUM>. The push rod sheath <NUM> is thus released. The driving spring <NUM> applies force on feature 107c on the push rod <NUM> and pushes the push rod sheath <NUM> together with push rod <NUM> downward. The downward movement of the push rod <NUM>, through the push disk feature 108c on the push rod <NUM>, causes the downward movement of a movable piston 111e and the pre-filled syringe <NUM>, due to hydraulic resistance. The first injection operation is enabled. Meantime, a syringe supporting spring <NUM>, located between the flange feature 111c on the pre-filled syringe <NUM> and a landing feature 103a on the lower cylinder <NUM>, is compressed. The downward movement of the pre-filled syringe <NUM> stops when the syringe supporting spring <NUM> is fully compressed. Or, the downward movement of the pre-filled syringe may be stopped by when the flange feature 111c meets with a stopping feature on the lower cylinder <NUM>. When the push rod <NUM> moves downward, the first pair of one-way bendable arms 108a pass through the stopping disk <NUM>. <FIG> show the re-setting or re-arming of the device assembly <NUM>. Before the re-arming operation, the end unit <NUM> is re-assembled with the device assembly <NUM> in a reversed direction in order to utilize the opening portion 104a on the end unit <NUM> to cover the needle 111d on the pre-filled syringe <NUM>. During the re-arming operation, the upper cylinder <NUM> is pushed distally and the separation spring <NUM> is compressed, so that the upper cylinder <NUM> is re-engaged with the retaining feature 107a on the push rod sheath <NUM>. When the distal pushing force on the upper cylinder <NUM> is removed, the separation spring <NUM> pushes the upper cylinder <NUM> upward. Because of the retaining feature 107a, the push rod sheath <NUM> also moves upward accordingly. In absence of downward pushing force, the syringe support syringe <NUM> moves the pre-filled syringe <NUM>, through flange feature 111c, and the stopping disk <NUM> to an upper position. The upward movement of the stopping disk <NUM> stops at a blocking feature 103c on the lower cylinder <NUM>. Because of the stopping disk <NUM> and the one-way bendable arms 108a, the upward movement of the push rod <NUM> is also stopped. Consequently, the push rod <NUM> is pulled and extended out from the push rod sheath <NUM> and the second pair of the one-way bendable arm 108b pass out of the push rod sheath <NUM>. With reference to <FIG>, during the second injection, the push cap <NUM> is pushed distally and the retaining feature 107a have cleared from the upper cylinder <NUM>, again. The push rod sheath <NUM> is thus released. The driving spring <NUM> applies force on the feature 107c on the push rod sheath <NUM> and pushes the push rod sheath <NUM> downward. This time, the downward movement of the feature 107c on the push rod sheath <NUM> applies pushing force on the second pair of the one-way bendable arm 108b on the push rod <NUM> to cause the push rod <NUM> move downward. The downward movement of the push rod <NUM>, through the push disk feature 108c on the push rod <NUM>, causes the further downward movement of a movable piston 111e and downward movement of the pre-filled syringe <NUM>, due to hydraulic resistance. The second injection operation is enabled. With the same operation mechanism, more than two pairs of one-way bendable arms can be placed on the push rod <NUM> in order to conduct more than two sequential injections by using the device assembly <NUM>. <FIG> show another configuration of the exemplary automatic medication injection device assembly <NUM>. In this configuration, instead of using the pre-filled syringe <NUM> with a staked needle, a pre-filled syringe <NUM> with luer lock connection is used. Before injection, the pre-filled syringe <NUM> is sealed by a luer lock tip cap 112a and a movable piston 112b. During injection, the luer lock tip cap 112a is removed and a luer lock needle <NUM> is assembled together with the pre-filled syringe <NUM>.

<FIG> illustrate the construction and function mechanism of the first alternative automatic medication injection device assembly <NUM> according to the invention. In this exemplary automatic medication injection device assembly <NUM>, a pre-filled cartridge <NUM> is used as medication container. A push cap <NUM>, placed at the proximal end of the device assembly <NUM>, is used to activate an automatic injection. The push cap <NUM> is assembled together with an upper cylinder <NUM>. The upper cylinder <NUM> is further assembled with a lower cylinder <NUM>. There is a separation spring <NUM> between the upper cylinder <NUM> and the lower cylinder <NUM> and landed on a landing feature 203a on the lower cylinder <NUM>. Inside the device assembly <NUM>, there is a push rod assembly. With reference to <FIG>, the push rod assembly includes a push rod sheath <NUM>, a push rod <NUM> and a stopping disk <NUM>. On the push rod <NUM>, there are five pairs of one-way bendable arms, 207a, 207b, 207c, 207d and 207e. At the distal end of the push rod <NUM>, there is a push disk feature 207f. At the proximal end of the push rod sheath <NUM>, there are two fingers which are provided with outwardly projecting retaining feature indicated by 204a. Opening feature 204b is provided on the push rod sheath <NUM> for resting the one-way bendable arms. At the distal end of the push rod sheath <NUM>, there is a landing feature 204c. A compressed driving spring <NUM> is placed between the landing feature 204c and the upper cylinder <NUM>. With reference to <FIG>, before use, a double ended needle <NUM>, for example, insulin pen needle, is assembled with a cartridge sheath <NUM>, and the double ended needle <NUM> penetrates the septum 209b on the pre-filled cartridge <NUM>. With reference to <FIG>, during the first injection, the push cap <NUM> is pushed distally. The push cap <NUM> is provided with preferably an annular projection, which is arranged to squeeze the retaining feature 204a at the proximal end of push rod sheath <NUM> so that retaining feature 204a have cleared from the upper cylinder <NUM>. The push rod sheath <NUM> is thus released. The driving spring <NUM> applies force on the landing feature 204c on the push rod sheath <NUM> and pushes the push rod sheath <NUM> and push rod <NUM> downward. The downward movement of the push rod <NUM>, through the push disk feature 207f on the push rod <NUM>, causes the downward movement of a movable piston 209a and the cartridge sheath <NUM> and the pre-filled cartridge <NUM> and the double ended needle <NUM>, due to hydraulic resistance. The first injection operation is enabled. Meantime, a cartridge supporting spring <NUM>, located between the flange feature 211a on the cartridge sheath <NUM> and a landing feature 203c on the lower cylinder <NUM>, is compressed, and the first pair of one-way bendable arms 207a pass through the stopping disk <NUM>. <FIG> show the re-setting or re-arming of the device assembly <NUM>. Before the re-arming operation, the double ended needle <NUM> is removed. During the re-arming operation, the upper cylinder <NUM> is pushed distally and the separation spring <NUM> is compressed, so that the upper cylinder <NUM> is re-engaged with the retaining feature 204a on the push rod sheath <NUM>. When the distal pushing force on the upper cylinder <NUM> is removed, the separation spring <NUM> pushes the upper cylinder <NUM> upward. Because of the retaining feature 204a, the push rod sheath <NUM> also moves upward accordingly. In absence of downward pushing force, the cartridge support spring <NUM> moves the cartridge sheath <NUM> and the pre-filled cartridge <NUM> and the stopping disk <NUM>, through flange feature 211a, to an upper position. The upward movement of the stopping disk <NUM> stops at a blocking feature 203b on the lower cylinder <NUM>. Because of the stopping disk <NUM> and the one-way bendable arms 207a, the upward movement of the push rod <NUM> is also stopped. Consequently, the push rod <NUM> is pulled and extended out from the push rod sheath <NUM> and the second and third pairs of the one-way bendable arm 207b and 207c passes out of the push rod sheath <NUM>. Before the second injection, a new double ended needle <NUM> is assembled with the device assembly <NUM>. With reference to <FIG>, during the second injection, the push cap <NUM> is pushed distally and the retaining feature 204a have cleared from the upper cylinder <NUM>, again. The push rod sheath <NUM> is thus released. The driving spring <NUM> applies force on the landing feature 204c on the push rod <NUM> and pushes the push rod sheath <NUM> downward. This time, the downward movement of the landing feature 204c applies pushing force on the third pair of the one-way bendable arm 207c on the push rod <NUM> to cause the push rod <NUM> move downward. The downward movement of the push rod <NUM>, through the push disk feature 207f on the push rod <NUM>, causes the further downward movement of the movable piston 209a and downward movement of the pre-filled cartridge <NUM> and the cartridge sheath <NUM> and the double ended needle <NUM>. The second injection operation is enabled. Meantime, the second pair of one-way bendable arms 207b pass through the stopping disk <NUM> and will provide the function of arms 207a, for the next step operation. <FIG> shows the device assembly <NUM> before the third injection and <FIG> shows the device assembly <NUM> during the third injection. For the third injection, the downward push force from the push rod sheath <NUM> is applied on the fifth pair of the one-way bendable arm 207e.

<FIG> illustrate the construction and function mechanism of the second alternative automatic medication injection device assembly <NUM> according to the invention. In this exemplary automatic medication injection device assembly <NUM>, the pre-filled cartridge <NUM> is used as medication container. A push cap <NUM>, placed at the proximal end of the device assembly <NUM>, is used to activate an automatic injection. The push cap <NUM> is assembled together with an upper cylinder <NUM>. The upper cylinder <NUM> is further assembled with a lower cylinder <NUM>. A dose setting window 303a being defined on the lower cylinder <NUM>. There is a separation spring <NUM> between the upper cylinder <NUM> and the lower cylinder <NUM>. Inside the device assembly <NUM>, there is a push rod assembly. With reference to <FIG>, the push rod assembly includes a position blocker <NUM> and a push rod <NUM>. On the push rod <NUM>, there is positioning track feature 307d. In the positioning track feature 307d, there are a plurality of indexed spaced-apart position setting features 307da. A protrusion feature 304b on the position blocker <NUM> is locked in the different individual position setting feature 307da for multiple injections. In order to move the position blocker <NUM> to different position along the push rod <NUM>, user pushes the push a tab feature 304a on the position blocker <NUM> inward (toward to the center of the device assembly <NUM>). Then, the protrusion feature 304b is dislocated out from the position setting feature 307da and the position blocker <NUM> can be moved along the longitudinal axis of the push rod <NUM>. When the position blocker <NUM> is moved to the next position, the push tab feature 304a is released and the protrusion feature 304b is locked in a different position setting feature 307da. <FIG> show the position blocker <NUM> is at different locations. At the distal end of the position blocker <NUM>, there is a push disk feature 304c. A compressed driving spring <NUM> is placed between a landing feature 307b on the push rod <NUM> and the upper cylinder <NUM>. With reference to <FIG>, during an injection, the push cap <NUM> is pushed distally. The push cap <NUM> is provided with preferably an annular projection, which is arranged to squeeze the retaining feature 307a at the proximal end of push rod <NUM> so that the retaining feature 307a have cleared from the upper cylinder <NUM>. The push rod <NUM> is thus released. The driving spring <NUM> applies force on the landing feature 307b on the push rod <NUM> and pushes the push rod <NUM> together with the position blocker <NUM> downward. The downward movement of the push rod <NUM>, through an end feature 307c, causes the downward movement of the movable piston 209a and the cartridge sheath <NUM> and the pre-filled cartridge <NUM> and the double ended needle <NUM> due to hydraulic resistance. Thus, an injection operation is enabled. Meantime, a cartridge supporting spring <NUM>, located between the flange feature 211a on the cartridge sheath <NUM> and a landing feature 303a on the lower cylinder <NUM>, is compressed. The downward movement of the position blocker <NUM> stops when the cartridge supporting spring <NUM> is fully compressed, and one of multiple injections is completed. <FIG> show the re-setting or re-arming of the device assembly <NUM>. Before the re-arming operation, the double ended needle <NUM> is removed. During the re-arming operation, the upper cylinder <NUM> is pushed distally and the separation spring <NUM> is compressed, so that the upper cylinder <NUM> is re-engaged with the retaining feature 307a on the push rod <NUM>. When the distal pushing force on the upper cylinder <NUM> is removed, the separation spring <NUM> pushes the upper cylinder <NUM> upward. Because of the retaining feature 307a, the push rod <NUM> also moves upward accordingly. In absence of downward pushing force, the cartridge support spring <NUM> moves the cartridge sheath <NUM> and the pre-filled cartridge <NUM>, through flange feature 211a, to an upper position. For the subsequential injection, user can move the position blocker <NUM> proximally in order to deliver more medication out of the pre-filled cartridge <NUM>.

<FIG> illustrate the construction and function mechanism of the third alternative automatic medication injection device assembly <NUM> according to the invention. In this exemplary automatic medication injection device assembly <NUM>, the pre-filled cartridge <NUM> is used as medication container. A push cap <NUM> is assembled with a dialing cylinder <NUM>, through a track 402a on the dialing cylinder <NUM>. This engagement prevents accidental activation of the device before use. A dose setting window 403a being defined on a scale cylinder <NUM>. During use, the dialing cylinder <NUM> is rotated to set the injection dose. With reference to <FIG>, user sets the location of a stopping ring <NUM> in order to get the different injection doses. Meantime, before injection, the automatic medication injection device assembly <NUM> is shown with a push rod <NUM> in a locked state, against biasing force of a driving spring <NUM>, by a releasable latch mechanism formed between a retaining feature 407a on the push rod <NUM> and the dialing cylinder <NUM>. The pre-filled cartridge <NUM> is assembled together with the scale cylinder <NUM> through the cartridge sheath <NUM>. <FIG> shows the engagements between the push rod <NUM> and the dialing cylinder <NUM>. A rectangular shape channel feature 402a on the dialing cylinder <NUM> engages with flat surfaces 407b on the push rod <NUM>. When user rotates the dialing cylinder <NUM>, the push rod <NUM> rotates accordingly. The rectangular shape channel feature 402a further provides landing surface for the releasable retaining feature 407a on the push rod <NUM>. <FIG> shows engagements among the push rod <NUM>, the stopping ring <NUM> and the scale cylinder <NUM>. During the dose setting, user rotates the dialing cylinder <NUM> and the push rod <NUM> relative to the scale cylinder <NUM>. Because of a thread feature 407c on the push rod <NUM>, when the push rod <NUM> rotates, the stopping ring <NUM> moves up and down along axial of the device, through the thread engagement between the push rod <NUM> and stopping ring <NUM>. The location of the stopping ring <NUM> can be viewed through viewing window 403a on the scale cylinder <NUM>. Due to the constrain engagement between groove feature 404a on the stopping ring <NUM> and rail feature 403b on the scale cylinder <NUM>, the stopping ring <NUM> can only moves axially, but not radially along the push rod <NUM> during dose setting and during injection. <FIG> shows the engagement between the dialing cylinder <NUM> and the scale cylinder <NUM>. In operation steps other than the dose setting step, the dialing cylinder <NUM> is always locked with the scale cylinder <NUM> together, through a tooth engagement between feature 402b on the dialing cylinder <NUM> and feature 403c on the scale cylinder <NUM>, or some other mechanism which allows the components to be connected and disconnected from each other. This tooth-type lock engagement prevents free rotation of the dialing cylinder <NUM> and restrain the radial movement and back-threading of the push rod <NUM> within the entire injection process. During the dose setting step, user pushes the dialing cylinder <NUM> distally relative to the scale cylinder <NUM>. Then, the locking engagement between 402b and 403c is disabled and the dialing cylinder <NUM> may be rotated relatively to the scale cylinder <NUM>. After the dose setting, when there is absent of pushing force toward distal end of the automatic medication injection device <NUM>, the dialing cylinder <NUM> is biased proximally and re-engaged with the scale cylinder <NUM>, due to the resilient force generated by a separation spring <NUM>. With reference to <FIG>, before injection, the double ended needle <NUM> is assembled with the cartridge sheath <NUM> and the pre-filled cartridge <NUM>. During injection, the push cap <NUM> is pushed toward to the distal end of the device, the releasable latch mechanism formed between the retaining feature 407a on the push rod <NUM> and the dialing cylinder <NUM> is released. The driving spring <NUM> drives the stopping ring <NUM> together with the push rod <NUM> to move toward the distal end of the automatic medication injection device <NUM>. The piston 209a is pushed downward. The cartridge <NUM> and the double ended needle <NUM> also move downward due to the hydraulic resistance. Consequently, liquid medication in the pre-filled cartridge <NUM> is injected from the device into patient's body. The stopping ring <NUM> meets with the cartridge sheath <NUM>. The first dose is delivered accordingly. During the re-setting or re-arming operation, the dialing cylinder <NUM> is pushed distally relative to the scale cylinder <NUM> in order to re-engage the dialing cylinder <NUM> with the push rod <NUM>. During this re-arming, the separation spring <NUM> is compressed. With reference to <FIG>, after the remove the distal toward force, the separation spring <NUM> pushes the dialing cylinder <NUM> and the push rod <NUM> back to the pre-injection position. A supporting spring <NUM> will push the cartridge sheath <NUM> and the cartridge <NUM> back to pre-injection position. Then, after setting another dose through locating the stopping ring to a more proximal location and assembling a new double ended needle, the device is ready for a subsequential injection.

<FIG> illustrate the construction and function mechanism of the fourth alternative automatic medication injection device assembly <NUM> according to the invention. This exemplary automatic medication injection device assembly <NUM> has the same functional mechanisms as the automatic medication injection device assembly <NUM>. Differently, a pre-filled syringe <NUM> is used as medication container. The pre-filled syringe <NUM> has a pierceable needle shield 509c. During the injection, user doesn't need to remove the needle shield 509c. The needle 509b can penetrate the needle shield 509c for medication injection. Compared with the automatic medication injection device assembly <NUM>, in the automatic medication injection device assembly <NUM>, separation spring <NUM> is changed to separation spring <NUM>; driving spring <NUM> is changed to driving spring <NUM>; push rod <NUM> is changed to push rod <NUM>; supporting spring <NUM> is changed to supporting spring <NUM>; and scale cylinder <NUM> is changed to scale cylinder <NUM>. An end unit <NUM> can be used in a similar way to the end unit <NUM>, during re-arming operation of the injection device.

Claim 1:
A medical injection device (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a distal end and a proximal end, comprising:
a medication container (<NUM>, <NUM>, <NUM>, <NUM>) having a movable piston (111e, 112b, 209a, 509a);
a cylinder (<NUM>, <NUM>, <NUM>, <NUM>) at said proximal end of said medical injection device and a cylinder (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at said distal end of said medical injection device;
a push rod assembly displaceably disposed in said medical injection device, said push rod assembly having a plurality of spaced-apart position setting means disposed along the length thereof, said push rod assembly selectively displacing said movable piston (111e, 112b, 209a, 509a) to dispense a medicament from said medication container (<NUM>, <NUM>, <NUM>, <NUM>);
a first resilient member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to bias said push rod assembly to move toward said distal end of said medical injection device;
a releasable restraining means (107a, 204a, 307a, 407a, 507a) configured to releasably restrain said push rod assembly in a locked state against said biasing of said first resilient member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), wherein, upon release of said releasable restraining means (107a, 204a, 307a, 407a, 507a), said push rod assembly moves under force of said first resilient member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) toward said distal end of said medical injection device;
a push cap (<NUM>, <NUM>, <NUM>, <NUM>) configured to release said releasable restraining means (107a, 204a, 307a, 407a, 507a); and
characterized by
an arming means comprising a second resilient member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to move said push rod assembly toward said proximal end of said medical injection device.