Abstract:
A liquid medicine self-administration device including a flexible reservoir, an operating member, a pushing member to move with respect to the operating member and to induce pressure deformation of the reservoir, and engaging means engages the operating member. With the operating member engaged by the engaging means, the pushing member is relatively moved to the operating member based on restoring force of a spring member to push the reservoir by the pushing member. By disengaging means moving in unison with the pushing member, the engaging means is released from an engaged state with respect to the operating member, when the pushing member has moved to a predetermined location while pushing the reservoir.

Description:
INCORPORATED BY REFERENCE 
       [0001]    The disclosure of Japanese Patent Application No. 2009-075043 filed on Mar. 25, 2009 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates in general to a self-administration device for liquid medicines, and in particular to an improvement to a liquid medicine self-administration device that enables a patient to self-administer a liquid medicine such as an analgesic or anesthetic. 
         [0004]    2. Description of the Related Art 
         [0005]    In the field of anesthesiology, administration of liquid medicines by an epidural catheter insertion method employing a low-dose continuous injection instrument has come into use in recent years as a way to alleviate pain such as postoperative or cancerous pain. However, due to variability in medical condition or constitution among patients, there will be instances in which a patient may report sudden severe pain despite being continuously administered a low dose of an analgesic. Accordingly, currently in development are liquid medicine self-administration devices which allow a patient to self-administer a large dose of an analgesic in a single shot in order to rapidly treat such occasional symptoms. 
         [0006]    Given this background, the Applicant previously proposed a liquid medicine self-administration device having a number of outstanding features (see U.S. Pat. No. 6,213,981). This liquid medicine self-administration device includes a cylindrical housing (casing) wherein a base member (port portion) having a liquid medicine inlet/outlet port and capable of flexural deformation is attached fitting into one open end of the housing, and pushing means is inserted into the other open end so as to be slidable in the axial direction. Within the housing there is accommodated a reservoir of pouch form that, when arranged with an opening thereof communicating with the liquid medicine inlet/outlet port of the base member, is closed by the base member and retains liquid medicine that has been injected through the liquid medicine inlet/outlet port. By then sliding the pushing means, through flexural deformation of the reservoir induced by being pushed by the pushing means, the liquid medicine retained within the reservoir will be expelled through the inlet/outlet port. Using this liquid medicine self-administration device, the patient can push and slide the pushing means in order to self-administer a one-time large dose of a liquid medicine containing an analgesic or the like. 
         [0007]    With such a liquid medicine self-administration device, the pushing means in particular is composed of a cylindrical operating member (operating member) that has been slidably inserted into a first open end of the housing, and a spring member housed inside the operating member and adapted to undergo elastic deformation when the operating member is slid towards the base member end. Engaging means is also provided for engaging (locking) the operating member when the operating member has reached a slide end position situated at the base member end, so that the operating member is non-slidably locked. With the operating member in the locked state, the reservoir will undergo pressure deformation due to the restoring force of the elastically deformed spring member. 
         [0008]    Using such a liquid medicine self-administration device, the patient need merely push the operating member until it is locked by the engaging means; subsequently, through the restoring force of the spring member, the liquid medicine that was retained in the reservoir will be administered to the patient automatically under constant pressure. For this reason, in contrast to the case where a conventional liquid medicine self-administration device lacking such engaging means is used, it is unnecessary for the patient to continue to push the pushing means until the entire amount of liquid medicine inside the reservoir has been completely expelled, and it is also possible to avoid abrupt expulsion of liquid medicine from the reservoir due to the pushing means having been pushed with excessive force. Consequently, through the use of the proposed liquid medicine self-administration device, even a patient with diminished physical strength will be able to self-administer liquid medicine in a stable and reliable manner, and it will be possible to effectively prevent liquid medicine from leaking due to being expelled too abruptly. 
         [0009]    The liquid medicine self-administration device has been designed so that, through a manual operation performed after the liquid medicine in the reservoir has been expelled to release the operating member from the locked state of engagement by the engaging means, the reservoir will recover to its condition prior to deformation through the pressure of injection of liquid medicine into the reservoir. In association with the recover of the reservoir, the operating member will return from the slide end position to its position prior to being pushed. Thus, in the event that the patient has forgotten to perform the unlocking operation, it will be necessary to perform unlocking and to then wait until the reservoir has refilled with liquid medicine before the next shot of liquid medicine can be administered. 
       SUMMARY OF THE INVENTION 
       [0010]    It is therefore one object of this invention to provide a liquid medicine self-administration device of improved construction whereby once the liquid medicine in the reservoir has been expelled, the operating member will be released automatically from its state of engagement with the engaging means, so that the reservoir may be refilled with liquid medicine, without the need to perform any kind of manual operation. 
         [0011]    One aspect of the present invention provides a liquid medicine self-administration device comprising: a housing open at both ends; a base member having a liquid medicine inlet/outlet port and attached fitting into a first open end of the housing; a flexible reservoir having an open end and a closed end wherein the open end is closed by the base member, arranged accommodated within the housing with the interior in communication with the liquid medicine inlet/outlet port of the base member and adapted to retain liquid medicine that has been injected therein through the liquid medicine inlet/outlet port; an operating member inserted through another open end of the housing and adapted to undergo movement into proximity with and away from the reservoir through an operation performed from an outside; engaging means adapted to engage the operating member when the operating member has moved into proximity with the reservoir and to prevent movement of the operating member; a pushing member accommodated in the housing interior between the operating member and the reservoir so as to be capable of relative movement with respect to the operating member, and adapted, through relative movement with respect to the operating member, to push against and induce flexural deformation of the reservoir causing liquid medicine inside the reservoir to be expelled from the liquid medicine inlet/outlet port; a spring member arranged within the housing in such a way as to undergo elastic deformation between the operating member and the pushing member through movement of the operating member into proximity with the reservoir, and to exhibit restoring force from an elastically deformed state in which the operating member has been engaged by the engaging means so that the relative movement of the pushing member with respect to the operating member resulting from the restoring force causes the reservoir to be pushed by the pushing member; and disengaging means arranged inside the housing so as to be capable of movement in unison with the pushing member and, when the pushing member has moved to a predetermined location while pushing the reservoir, functioning to release the engaging means from an engaged state with respect to the operating member. 
         [0012]    In one preferred form of the present invention, the disengaging means is composed of a disengaging projection integrally projecting towards the base member end from the pushing member; the engaging means includes an engaging portion disposed on the operating member, a flexing member capable of flexural deformation non-displaceably disposed between the reservoir and the pushing member, an engaging claw portion projecting from the flexing member and adapted to engage the engaging portion of the operating member, and a sloping face adapted to be pushed by the disengaging projection when the operating member has moved towards the reservoir end and to bring about flexural deformation of the flexing member; and the engaging claw portion is released from the engaged state with respect to the engaging portion of the operating member through flexural deformation of the flexing member in association with pushing of the sloping face by the disengaging projection. 
         [0013]    Where the design of the engaging means includes the flexing member as described above, preferably, the flexing member is composed of a split ring; and the engaging claw portion is released from the engaged state with respect to the engaging portion of the operating member through flexion and diameter constriction of the split ring brought about by the disengaging projection of the pushing member pushing against the sloping face. 
         [0014]    In another preferred form of the invention, the engaging means is situated housed inside the housing having a window; and the operating member is furnished with an operating projection that projects to the housing exterior through the window so that, with the engaging claw portion in the engaged state with respect to the engaging portion of the operating member, the flexing member undergoes flexural deformation when the operating projection is pushed from the outside, in order to release the engaging claw portion from the engaged state with respect to the engaging portion of the operating member. 
         [0015]    Another aspect of the present invention provides a liquid medicine self-administration device including a flexible reservoir having a liquid medicine inlet and a liquid medicine outlet and adapted to retain a prescribed amount of liquid medicine in an interior thereof, and pushing means adapted to induce pressure deformation of the reservoir and expel liquid medicine inside the reservoir from the liquid medicine outlet, wherein the improvement comprises: the pushing means having an operating member adapted to undergo movement into proximity with and away from the reservoir through an operation performed from an outside, and a pushing member adapted to undergo relative movement with respect to the operating member and to induce pressure deformation of the reservoir; engaging means adapted to engage the operating member when the operating member has moved into proximity with the reservoir and to prevent movement of the operating member; a spring member adapted to undergo elastic deformation through movement of the operating member towards the reservoir, and with the operating member engaged by the engaging means, to produce relative movement of the pushing member with respect to the operating member on the basis of restoring force from the elastically deformed state so that the reservoir is pushed by the pushing member; and disengaging means adapted to move in unison with the pushing member and, when the pushing member has moved to a predetermined location while pushing the reservoir, to release the engaging means from the engaged state with respect to the operating member. 
         [0016]    With the liquid medicine self-administration device according to the present invention, simply by pushing the operating member so that it is engaged by the engaging means and becomes locked thereby, the reservoir will undergo flexural deformation while pushed by the pushing member due to the restoring force of the spring member, thus causing liquid medicine retained inside the reservoir to be expelled automatically at constant pressure. Then, once the pushing member has moved to a prescribed position while pushing on the reservoir, the operating member will be disengaged from the engaging means by the disengaging means so that the operating member again assumes a slidable state. The spring member is thereby released from a state of elastic deformation, whereupon the spring member recovers and pushing of the reservoir by the pushing member due to the restoring force of the spring member ceases. In this state, owing to injection pressure of liquid medicine into the reservoir through the liquid medicine inlet, the reservoir will recover from a state of flexural deformation, and liquid medicine will again fill the reservoir interior. 
         [0017]    According to the liquid medicine self-administration device of the present invention, by only setting the movement zone of the pushing member when engagement of the operating member by the engaging means is released by the engaging means to the movement zone of the pushing member when expulsion of liquid medicine inside the reservoir is complete, engagement of the operating member by the engaging means, i.e., locking of the operating member, can be released automatically at the point in time that liquid medicine inside the reservoir is finished being expelled. This makes it possible for the reservoir interior to refill with liquid medicine without the need to perform any manual operation. As a result, it is possible to effectively eliminate situations where administration of a subsequent shot of liquid medicine cannot take place due to having neglected to unlock the operating member, thus affording further enhanced ease of use in a very advantageous manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The foregoing and/or other objects features and advantages of the invention will become more apparent from the following description of a preferred embodiment with reference to the accompanying drawings in which like reference numerals designate like elements and wherein: 
           [0019]      FIG. 1  is a longitudinal sectional view depicting one embodiment of a liquid medicine self-administration device according to the present invention; 
           [0020]      FIG. 2  is an exploded perspective view of the liquid medicine self-administration device of  FIG. 1 , shown with the housing removed; 
           [0021]      FIG. 3  is a longitudinal sectional view of a base member which is part of the liquid medicine self-administration device of  FIG. 1 , taken along line  3 - 3  in  FIG. 4 ; 
           [0022]      FIG. 4  is an illustration viewed in the direction of arrow  4  in  FIG. 3 ; 
           [0023]      FIG. 5  is a longitudinal sectional view of a reservoir ring which is part of the liquid medicine self-administration device of  FIG. 1 , taken along line  5 - 5  in  FIG. 6 ; 
           [0024]      FIG. 6  is an illustration viewed in the direction of arrow  6  in  FIG. 5 ; 
           [0025]      FIG. 7  is a longitudinal sectional view of a reservoir which is part of the liquid medicine self-administration device of  FIG. 1 , taken along line  7 - 7  in  FIG. 8 ; 
           [0026]      FIG. 8  is an illustration viewed in the direction of arrow  8  in  FIG. 7 ; 
           [0027]      FIG. 9  is a longitudinal sectional view of a split ring which is part of the liquid medicine self-administration device of  FIG. 1 , taken along line  9 - 9  in  FIG. 10 ; 
           [0028]      FIG. 10  is an illustration viewed in the direction of arrow  10  in  FIG. 9 ; 
           [0029]      FIG. 11  is a longitudinal sectional view of a plunger which is part of the liquid medicine self-administration device of  FIG. 1 , taken along line  11 - 11  in  FIG. 12 ; 
           [0030]      FIG. 12  is an illustration viewed in the direction of arrow  12  in  FIG. 11 ; 
           [0031]      FIG. 13  is an illustration depicting a liquid medicine administration system that includes the liquid medicine self-administration device of  FIG. 1  connected to a liquid medicine receptacle; 
           [0032]      FIG. 14  is a drawing depicting a usage condition of the liquid medicine self-administration device of  FIG. 1 , and shows a condition immediately following pushing of a push button; 
           [0033]      FIG. 15  is an enlarged fragmentary view of a part  15  in  FIG. 14 ; 
           [0034]      FIG. 16  is a drawing depicting another usage condition of the liquid medicine self-administration device of  FIG. 1 , and shows a condition in which, following pushing of the push button, the plunger has moved to the reservoir and induced pressure deformation of the reservoir; 
           [0035]      FIG. 17  is an enlarged fragmentary view of a part  17  in  FIG. 16 ; 
           [0036]      FIG. 18  is a drawing depicting another embodiment of the liquid medicine self-administration device according to the present invention and corresponds to  FIG. 5 ; and 
           [0037]      FIG. 19  is a drawing depicting yet another embodiment of the liquid medicine self-administration device according to the present invention and corresponds to  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    First,  FIG. 1  depicts a longitudinal sectional view of one embodiment of a liquid medicine self-administration device according to the present invention; and  FIG. 2  depicts an exploded perspective view thereof. It will be appreciated from the drawings that the liquid medicine self-administration device of the present embodiment has a housing  10 , a reservoir unit  12 , a split ring  14  provided as a flexing member, a plunger  16  provided as a pushing member, a helical compression spring  18  provided as a spring member; and a push button  20  provided as an operating member. In  FIG. 2 , the housing  10  is shown removed. 
         [0039]    Turning to a more detailed description, the housing  10  is a cylindrical member of approximately round cylindrical shape extending in the vertical direction in  FIG. 1 , and made using synthetic resin material, for example, polyethylene, polypropylene, polyester, polyvinyl chloride, polycarbonate, or polyacetal. For convenience, hereinbelow the direction corresponding to the vertical direction of  FIG. 1  in the liquid medicine self-administration device of the present embodiment shall be referred to as the vertical direction. 
         [0040]    In this cylindrical housing  10 , the lower end portion has tapered cylindrical shape progressively smaller in diameter towards the bottom so that the opening at the lower end is smaller in diameter than the opening at the upper end. In zones situated in diametrical opposition in the axially medial portion of the housing  10  there are formed slits  22  that extend for mutually identical length in the axial direction, with one being formed in each of the zones. A window  24  of oblong shape is formed to the lower side of one of the slits  22  in the housing  10  and passes completely through the lower end of the housing  10 . 
         [0041]    The reservoir unit  12  fits inside the lower end part of the housing  10 . The reservoir unit  12  is composed of a base member  26 , a reservoir  28 , and a reservoir ring  30 . The base member  26  is a molded resin component made using resin material comparable to the material forming the housing  10 . As shown in  FIGS. 2 to 4 , the base member  26  integrally incorporates a mounting ring portion  32 , and a port portion  34  having a round cylindrical outside peripheral face positioned concentrically to the inside of this mounting ring portion  32  and linked to the mounting ring portion  32  by a linking portion  33  of annular disk shape. Between the mounting ring portion  32  and the port portion  34  there is defined a groove portion  36  of approximately annular form whose respective side walls are defined by the inside peripheral face and outside peripheral face of these portions and whose basal portion is defined by the linking portion  33  so that the mounting ring portion  32  is elastically deformable diametrically inward. 
         [0042]    The port portion  34  of the base member  26  is provided with a liquid medicine inlet port  38  provided as a liquid medicine inlet, and a liquid medicine outlet port  40  provided as a liquid medicine outlet, these being disposed so as to pass completely through the port portion  34  in the vertical direction. The liquid medicine inlet port  38  and the liquid medicine outlet port  40  are also designed as liquid medicine inlet/outlet ports. As depicted in  FIG. 1 , a constant pressure-opening valve  42  is fitted into the interior of the liquid medicine outlet port  40 . This constant pressure-opening valve  42  has a known art design adapted to open when pressure inside the liquid medicine outlet port  40  has reached a predetermined value. Here, in order to make possible continuous administration of a low dose of liquid medicine to the patient as described later, the constant pressure-opening valve  42  has been designed to open in response to a rise in pressure inside the liquid medicine outlet port  40  occurring when a small amount of liquid medicine is injected into the reservoir  28  through the liquid medicine inlet port  38 . On the upper end face of the mounting ring portion  32 , a hook portion  44  furnished at its distal end with a barb-shaped claw has been integrally formed projecting upright at each of four locations spaced equidistantly in the circumferential direction. 
         [0043]    The reservoir ring  30  is likewise a molded resin component made using resin material comparable to the material forming the housing  10  and the base member  26 . As shown in  FIGS. 5 and 6 , the reservoir ring  30  as a whole has an approximately round stepped cylindrical shape wherein the lower end section defines a large-diameter portion  46 , the upper end section defines a small-diameter portion  48 , and the axially medial portion defines a step portion  50  of shoulder form providing a stepped transition between the large-diameter portion  46  and the small-diameter portion  48 . An engagement recess  52  is formed at each of four locations spaced equidistantly in the circumferential direction of the step portion  50 . 
         [0044]    Meanwhile, the reservoir  28  is made using elastic materials such as elastomers, silicone rubber or other such synthetic rubbers, or natural rubber. As shown in  FIGS. 7 and 8 , the shape of the reservoir  28  as a whole is a bottomed, approximately round stepped cylindrical shape having an upper base panel and slightly smaller than the reservoir ring  30 . The upper section of the reservoir  28  defines a small-diameter portion  54  which is thin and readily elastically deformable, while the lower section defines a thick-walled large-diameter portion  56 , with a step portion  58  of shoulder form formed in the axially medial portion providing a stepped transition between the small-diameter portion  54  and the large-diameter portion  56 . 
         [0045]    As depicted in  FIGS. 1 and 2 , the reservoir  28  is arranged with the bottom end part of its large-diameter portion  56  intruding into the groove portion  36  of the base member  26  and with its large-diameter portion  56  fitting externally about the port portion  34 , with the bottom face of the step portion  58  positioned in contact about the entire circumference against the outside peripheral part of the upper end face of the port portion  34 . The reservoir ring  30  is slipped externally about the reservoir  28  so that their respective small-diameter portions  54 ,  48  correspond and their large-diameter portions  56 ,  46  correspond, with the step portion  50  of the reservoir ring  30  juxtaposed over the step portion  58  of the reservoir  28 , and the lower end part of the large-diameter portion  46  slipped into the groove portion  36  of the base member  26 . In this state, the four hook portions  44 ,  44 ,  44 ,  44  which integrally rise up from the mounting ring portion  32  of the base member  26  will respectively engage the four engagement recesses  52 ,  52 ,  52 ,  52  which have been provided to the step portion  50  of the reservoir ring  30 . 
         [0046]    By so doing the reservoir ring  30  is integrally attached to the base member  26  with the reservoir  28  held clasped between the base member  26  and the reservoir ring  30 . In this clasped state, the opening leading from the small-diameter portion  54  to the large-diameter portion  56  of the reservoir  28  will be closed off by the port portion  34  of the base member  26  so that the interior space of the small-diameter portion  54  defines a liquid medicine retaining portion  60  sealed off liquidtightly from the outside. This liquid medicine retaining portion  60  communicates with the outside only through the liquid medicine inlet port  38  and the liquid medicine outlet port  40 . The small-diameter portion  54  of the reservoir  28  which defines this liquid medicine retaining portion  60  is housed inside the small-diameter portion  48  of the reservoir ring  30  so that the small-diameter portion  48  protects the small-diameter portion  54  of the reservoir  28 . 
         [0047]    In this way, in the present embodiment, the reservoir unit  12  is constituted as an integral assembly of the base member  26 , the reservoir  28 , and the reservoir ring  30 . The reservoir unit  12  is then slipped into the housing  10  from its upper opening, and the mounting ring portion  32  of the base member  26 , placed in a state of elastic deformation diametrically inward, is disposed in pressure contact with the inside peripheral face of the lower end part of the housing  10  to secure it to the inside of the lower end part of the housing  10 . The base member  26  is thereby installed inside the lower opening of the housing  10 , with the reservoir  28  accommodated inside the lower end part of the housing  10 . The liquid medicine inlet port  38  and the liquid medicine outlet port  40  which have been provided to the port portion  34  of the base member  26  open to the outside through the lower opening of the housing  10 , and the liquid medicine retaining portion  60  of the reservoir  28  communicates with the outside through these two ports  38 ,  40 . 
         [0048]    The reservoir  28  employed in this instance is one with a small-diameter portion  54  capacity of about 3 mL, allowing about 3 mL of liquid medicine to be retained inside the liquid medicine retaining portion  60 . If the amount of liquid medicine to be retained within the liquid medicine retaining portion  60  of the reservoir  28  will be less than this, while not depicted in the drawings, for example, a reservoir having a small-diameter portion having the same diameter but lower height giving it smaller capacity could be incorporated into the reservoir unit assembly. On the other hand, if it is desired to increase the retained amount of liquid medicine within the liquid medicine retaining portion  60 , for example, a reservoir having a small-diameter portion having the same diameter but greater height giving it larger capacity could be incorporated into the reservoir unit assembly. In the present embodiment, the reservoir  28  is incorporated into the reservoir unit  12  assembly as described above, thereby allowing the reservoir  28  to be easily replaced, and allowing the capacity of the liquid medicine retaining portion  60  to be easily increased or decreased as well. 
         [0049]    As mentioned above, the split ring  14  is arranged to the inside of the lower end section of the housing  10  in which the reservoir unit  12  has been secured. This split ring  14  is composed, for example, of an elastically deformable molded resin article using resin material comparable to the material forming the housing  10 . As shown in  FIGS. 1 ,  9 , and  10 , the split ring  14  takes the form of a thin ring having outside diameter approximately equal to or slightly larger than the inside diameter of the housing  10 , which has been divided by removing a segment of prescribed circumferential length at a single location along the circumference. 
         [0050]    The section situated to the opposite side in the diametrical direction from this divided section of the split ring  14  is thicker in the diametrical direction, and an engaging hook  62  integrally projects up from the inside peripheral section of the end face of this thick portion. This engaging hook  62  has an extended portion  64  integrally extending upward from the end face of the split ring  14 , and an engaging claw portion  66  integrally formed at the distal end of this extended portion  64 . A sloping face  68  that slopes downwardly towards the outside in the diametrical direction of the split ring  14  is formed on the engaging claw portion  66 . This sloping face  68  is designed so that its lower edge is situated at the same location with the outside peripheral face of the split ring  14  with respect to the diametrical direction of the split ring  14 . An operating projection  70  of rectangular shape projects integrally out from the outside peripheral face of the split ring  14  in the zone thereof where the engaging hook  62  is formed. 
         [0051]    As shown in  FIG. 1 , the split ring  14 , oriented so that the engaging hook  62  extends upward and with its gap spread apart in the diametrical direction, is slipped externally about the small-diameter portion  48  of the reservoir ring  30  in the reservoir unit  12  which is situated to the inside of the lower end part of the housing  10 . In this state, the split ring  14 , having been placed in a state of constricted diameter through slight preliminary compression, is inserted into the housing  10  while positioning the operating projection  70  so as to project out through the window  24  which has been provided at the lower end of the housing  10 . Through engagement of the operating projection  70  against the inside peripheral face of the window  24  inside the lower end part of the housing  10 , the split ring  14  is fixedly positioned such that relative displacement in the circumferential and axial directions with respect to the housing  10  is not possible. 
         [0052]    Thus, when the operating projection  70  is subjected to pushing operation from the outside, the outside peripheral face of the split ring  14  will slide along the inside peripheral face of the housing  10  and the split ring  14  will flex and constrict in diameter, whereby the engaging hook  62  will undergo displacement inwardly in the diametrical direction of the split ring  14  (see  FIG. 17 ). If the sloping face  68  of the engaging hook  62  is subjected to downward pushing force, the split ring  14  will likewise flex and constrict in diameter, and the engaging hook  62  will undergo displacement inwardly in the diametrical direction of the split ring  14  (see  FIG. 17 ). 
         [0053]    Meanwhile, the push button  20  is inserted into the upper opening of the housing  10  as depicted in  FIGS. 1 and 2 . This push button  20  is a molded resin component made using resin material comparable to the material forming the housing  10 . Its one-sided bottomed round cylindrical shape is provided with an upper base portion  72 , and has outside diameter slightly smaller than the inside diameter of the housing  10  and length shorter than the housing  10 . In two zones situated in opposition in the diametrical direction of the cylindrical wall of the push button  20  there are provided slits  74 ,  74  that extend for mutually identical length in the axial direction. These slits  74 ,  74  have width and length identical to the slits  22 ,  22  which have been provided to the housing  10 . To the lower side (opening side) of one slit  74 , an engaging hole  76  of slit form provided as an engaging portion extending in the circumferential direction passes completely through the cylindrical wall. 
         [0054]    This push button  20  is then slipped inside the housing  10  through the upper opening of the housing  10 , so that its upper base part lies exposed to the outside through the upper opening of the housing  10 , and is positioned with the two slits  74 ,  74  of the push button  20  respectively aligned with the two slits  22 ,  22  of the housing  10 . With the push button  20  in this state of being slipped inside the housing  10 , it will be possible for it to slide in the vertical direction (axial direction) while sliding along the inside peripheral face of the housing  10 , with slide in the downward direction being permitted up to the point that the lower end face comes into abutment against the upper end face of the split ring  14 . When the push button  20  has been slid downward until reaching a bottom dead point location at which its lower end face is in abutment against the upper end face of the split ring  14 , the engaging claw portion  66  of the engaging hook  62  of the split ring  14  will intrude into the engaging hole  76  of the push button  20  so as to become engaged therein (see  FIG. 15 ). Through this engaged state the push button  20  will be prevented from sliding. 
         [0055]    The plunger  16  is housed between the push button  20  and the reservoir  28  in the axially medial part of the housing  10  interior. This plunger  16  is likewise made of appropriately selected material comparable to that of the housing  10 . As shown in  FIGS. 11 and 12 , the plunger  16  integrally incorporates a slide ring portion  78  of ring shape as a whole having outside diameter slightly smaller than the inside diameter of the push button  20 ; a pushing cylinder portion  80  of one-sided bottomed round cylindrical shape having a lower base portion and positioned coaxially to the inside of the slide ring portion  78  and spaced apart therefrom by a prescribed distance in an attitude extending out towards the bottom from the lower opening of the slide ring portion  78 ; and a linking portion  82  linking the slide ring portion  78  with the pushing cylinder portion  80 . 
         [0056]    In this plunger  16 , the lower face of the lower base part of the pushing cylinder portion  80  constitutes a pushing face  84  which is positioned in opposition in the axial direction to the upper base face of the reservoir  28 . Slide projections  86 ,  86  are provided integrally projecting respectively at two locations situated at either side of the outside peripheral face of the slide ring portion  78  in the diametrical direction. Additionally, in each of the two zones of the slide ring portion  78  in which these two slide projections  86 ,  86  are respectively disposed there is integrally formed one disengaging projection  88 , provided as disengaging means, which is defined by extending the section downward by a prescribed length. The inside angle part of the distal end part of the disengaging projection  88  is shaped as a convex curving angled part, giving it a rounded contour. 
         [0057]    As depicted in  FIG. 1 , in the interior of the housing  10 , the plunger  16  is positioned housed inside the lower opening of the push button  20 . The two slide projections  86 ,  86  which have been provided to the slide ring portion  78  of the plunger  16  insert into and pass through the two slits  74 ,  74  of the push button  20 , and respectively intrude into the slits  22 ,  22  of the housing  10 . The plunger  16  is thereby rendered immovable in the circumferential direction within the housing  10 , yet is capable of relative sliding in the axial direction (vertical direction) with respect to the push button  20  while guided by the slits  74 ,  22  which have been respectively provided in the push button  20  and the housing  10 . When the push button  20  experiences relative movement towards the top of the housing  10 , the two slide projections  86 ,  86  will become wedged between the upper ends of the slits  22 ,  22  of the housing  10  and the lower ends of the slits  74 ,  74  of the push button  20 , thus preventing the push button  20  from being pulled out from inside the housing  10 . 
         [0058]    As will be understood from  FIG. 1 , the helical compression spring  18 , which has shorter axial length than the push button  20 , is accommodated positioned coaxially inside the push button  20  in which the plunger  16  has been housed. This helical compression spring  18  is attached at one end thereof to a mounting portion  90  that has been integrally formed on the inside face of the upper base portion  72  of the push button  20  (not shown), while the other end is secured to the linking portion  82  of the plunger  16 . 
         [0059]    The plunger  16  is thereby attached to the upper base portion  72  of the push button  20  through the agency of the helical compression spring  18 . When the plunger  16  and the upper base portion  72  of the push button  20  have come into proximity through relative movement of the push button  20  and the plunger  16  in their respective axial directions, the helical compression spring  18  becomes compressed, and the restoring force produced thereby urges the push button  20  and the plunger  16  in the direction of their separation. 
         [0060]    Where the liquid medicine self-administration device of the present embodiment constructed as described above is to be placed in service, the liquid medicine inlet port  38  and the liquid medicine outlet port  40  of the base member  26  may be connected to a liquid medicine inlet tube  92  and a liquid medicine outlet tube  94  as depicted in  FIG. 13 , for example (the respective connection sections are not illustrated). The liquid medicine inlet tube  92 , at the end thereof opposite that connected to the liquid medicine inlet port  38 , is connected to the upstream end of a liquid medicine delivery tube  98  adapted to deliver to a catheter (not shown) or the like a prescribed liquid medicine such as an analgesic contained in a liquid medicine receptacle  96 ; while the liquid medicine outlet tube  94 , at the end thereof opposite that connected to the liquid medicine outlet port  40 , is connected to the downstream side. That is, in this instance, the liquid medicine self-administration device for providing an additional dose of liquid medicine is disposed in a parallel arrangement with the line composed of the liquid medicine delivery tube  98  for continuous administration of liquid medicine. Thus, continuous administration of liquid medicine may take place even while liquid medicine is retained in the liquid medicine retaining portion  60  of the liquid medicine self-administration device. In  FIG. 13 ,  100  denotes a flow control device for controlling the flow rate of liquid medicine inside the liquid medicine delivery tube  98 , and  102  denotes a port for connection of a syringe or the like. 
         [0061]    The discussion now turns to the method of use of the liquid medicine self-administration device of the present embodiment. 
         [0062]    First, with the liquid medicine self-administration device of the present embodiment connected in a parallel arrangement with the main line composed of the liquid medicine delivery tube  98  which leads from the liquid medicine receptacle  96  as depicted in  FIG. 13 , liquid medicine is continuously administered in a routine low dosage. 
         [0063]    In the event that the patient needs to self-administer a one-time large dose of liquid medicine, the patient pushes the push button  20  downward (the direction indicated by arrow A) so that it slides downward while sliding along the inside peripheral face of the housing  10  as depicted in  FIG. 14 . At this time, because the two slide projections  86 ,  86  of the plunger  16  have been inserted through the slits  74 ,  74  of the push button  20 , the push button  20  will slide straight ahead without axial rotation. Once the push button  20  has undergone sliding movement to the bottom dead point location at which its lower end face abuts against the upper end face of the split ring  14 , the engaging claw portion  66  of the engaging hook  62  integrally formed with the split ring  14  will intrude into the engaging hole  76  provided at the lower end of the push button  20  and become engaged therein as depicted in  FIGS. 14 and 15 . Thus, the push button  20  will become locked in a state in which sliding movement is not possible, so that the push button  20  is held in place at the bottom dead point. From the above description it will be appreciated that in the present embodiment, the engaging means includes the engaging hole  76  of the push button  20 , the engaging claw portion  66  of the engaging hook  62  of the split ring  14 , and the sloping face  68  of the engaging claw portion  66 . 
         [0064]    Meanwhile, in association with downward sliding movement of the push button  20  the plunger  16 , pushed by the helical compression spring  18 , will move downward and the pushing face  84  will come into abutment against the upper base part of the reservoir  28 . If the push button  20  experiences further downward sliding movement past this point, the helical compression spring  18  will become compressed between the upper base portion  72  of the push button  20  and the plunger  16 . 
         [0065]    Once the push button  20  is locked in the manner described above, starting at this point in time the helical compression spring  18  will begin to gradually expand due to restoring force. In association therewith, the plunger  16  will push against the small-diameter portion  54  of the reservoir  28  and will move downward while inducing small incremental flexural deformation thereof. Thus, liquid medicine  104  inside the liquid medicine retaining portion  60  of the reservoir  28  will be expelled out through the liquid medicine outlet port  40  and the liquid medicine outlet tube  94  connected thereto, and will pass through the liquid medicine delivery tube  98  to be delivered into the body of the patient through a catheter or the like. This expulsion of the liquid medicine  104  from the interior of the liquid medicine retaining portion  60  will proceed automatically on the basis of restoring force of the helical compression spring  18 . At this time the liquid medicine  104  inside the liquid medicine retaining portion  60  will continue to be administered in a larger amount than during routine low-dose continuous administration, and will do so at a constant level of pressure. From the above description it will be appreciated that in the present embodiment, the pushing means includes the push button  20  and the plunger  16 . 
         [0066]    Downward movement of the plunger  16  in association with such expansion of the helical compression spring  18  will cause the distal end part of the disengaging projection  88  which has been integrally formed with the plunger  16  to abut against the sloping face  68  of the engaging hook  62  as indicated by solid lines in  FIGS. 16 and 17 . As the plunger  16  moves further downward beyond this point, the disengaging projection  88  will move downward over the top of the sloping face  68  while pushing the sloping face  68  as indicated by double dot-and-dash lines in  FIG. 17 . The split ring  14  will thereby flex and constrict in diameter, and in association therewith the engaging hook  62  will experience displacement diametrically inward so that the engaging claw portion  66  disengages from the engaging hole  76  of the push button  20 , releasing the push button  20  from its non-slidably locked condition. At this point, pushing force exerted on the plunger  16  due to restoring force of the helical compression spring  18 , as well as pushing force on the reservoir  28  by the plunger  16 , will both cease, thereby automatically terminating the expulsion of liquid medicine from inside the liquid medicine retaining portion  60  in a greater amount and at higher pressure than during routine low-dose continuous administration. 
         [0067]    Subsequently, the small-diameter portion  54  of the reservoir  28  will recover to its condition prior to deformation through the pressure of injection of liquid medicine that is injected into the liquid medicine retaining portion  60  through the liquid medicine inlet port  38 , and the liquid medicine retaining portion  60  interior will refill with liquid medicine  104 . In association with this recovery of the small-diameter portion  54  of the reservoir  28 , the plunger  16 , the helical compression spring  18 , and the push button  20  will be lifted upward and again return to their positions shown in  FIG. 1 . This completes preparation for a subsequent one-time administration of a large dose of liquid medicine by a pushing operation of the push button  20 . 
         [0068]    In the liquid medicine self-administration device of the present embodiment, one-time administration of a large dose of liquid medicine  104  can be automatically effected simply by pushing the push button  20  until the push button  20  locks. Subsequently, at the point in time that one-time administration of a large dose of liquid medicine  104  is completed, the push button  20  will unlock automatically even without performing any unlocking operation of the push button  20 . Refilling of the liquid medicine retaining portion  60  of the reservoir  28  with liquid medicine  104  will then take place automatically as well. 
         [0069]    Accordingly, where the liquid medicine self-administration device of the present invention is employed, it will be possible to effectively eliminate situations in which one-time administration of a large dose of liquid medicine through subsequent pushing operation of the push button  20  cannot be carried out due to having neglected to unlock the push button  20 . A result of this is that further enhanced ease of use may be achieved a very advantageous manner. 
         [0070]    Additionally, with this liquid medicine self-administration device, locking of the push button  20  (i.e. engagement of the engaging hook  62  by the engaging hole  76 ) can be released automatically simply through a process whereby the sloping face  68  of the engaging hook  62  is pushed by the disengaging projection  88  integrally formed with the plunger  16 , owing to downward movement of the plunger  16  on the basis of restoring force of the helical compression spring  18 . For this reason, the mechanism for unlocking the push button  20  can be realized advantageously through a very simple construction having a minimum of parts. 
         [0071]    Furthermore, with the liquid medicine self-administration device of the present embodiment, the push button  20  may be unlocked manually through a push operation performed externally on the operating projection  70  to disengage the engaging hook  62  by the engaging hole  76 . Thus, if for some reason it should become necessary to urgently unlock the push button  20 , this can be accomplished quickly and reliably. Moreover, by unlocking the push button  20  manually during one-time administration of a large dose of the liquid medicine  104 , automatic expulsion of a large dose of the liquid medicine  104  can be forcibly brought to an emergency halt. 
         [0072]    Furthermore, with this liquid medicine self-administration device, through flexing and diameter constriction by the split ring  14 , the engaging claw portion  66  is disengaged from the engaging hole  76  of the push button  20 , unlocking the push button  20 . Thus, as compared to a design wherein, for example, the engaging claw portion  66  is provided to a flexing member of plate or rod form, and the engaging claw portion  66  is disengaged from the engaging hole  76  of the push button  20  through flexural deformation of this plate-shaped flexing member, not only does the split ring  14  exhibit better durability to withstand repeated flexural deformation, but a larger deformation stroke can be assured as well. As a result, unlocking of the push button  20  can take place in a stable and reliable manner, and the robustness of the device as a whole can be advantageously improved. 
         [0073]    While the present invention has been shown hereinabove in terms of certain specific arrangements, these are merely exemplary, and the invention is in no way limited by the disclosure herein. 
         [0074]    For example, the construction of the flexing member to which the engaging claw portion  66  is provided is not limited in any way to that shown herein by way of example. As an example, as depicted in  FIG. 18 , a plate-shaped flexing piece  106  extending integrally upward could be provided to the step portion  50  of the reservoir ring  30 , and the engaging claw portion  66  provided on the side face thereof. Alternatively, as depicted in  FIG. 19 , a plate-shaped flexing piece  106  extending integrally upward could be provided to the mounting ring portion  32  of the base member  26 , and the engaging claw portion  66  provided on the side face thereof. Also, while not illustrated in the drawings, the plate-shaped flexing piece  106  integrally formed on the reservoir ring  30  or the base member  26  could be designed to undergo flexural deformation sideways, namely, in the axis-perpendicular direction, when the sloping face  68  provided to the engaging claw portion  66  is pushed by the disengaging projection  88  of the plunger  16 . By so doing, the engaging claw portion  66  provided to the plate-shaped flexing piece  106  will separate from the engaging hole  76  of the housing  10  so that the engaging claw portion  66  disengages from the engaging hole  76 . 
         [0075]    It is possible in this way for the flexing member to be constituted as a flexing piece disposed at a fixed location so as to extend in the axial direction inside the housing  10 . By so doing, the flexing member can be provided integrally with the other members, thereby advantageously affording a reduction in the number of parts. Moreover, with regard to the reservoir ring  30  depicted in  FIG. 18  and the base member  26  depicted in  FIG. 19 , components and parts of similar construction to those in the reservoir ring  30  depicted in  FIG. 5  and the base member  26  depicted in  FIG. 3  have been assigned the same symbols used in  FIGS. 5 and 3 , and are not described in any detail. 
         [0076]    In the preceding embodiment, the base member  26  was provided respectively with a liquid medicine inlet port  38  and a liquid medicine outlet port  40 ; however, as shown for example in FIG. 6 of U.S. Pat. No. 6,213,981, it would be possible to instead provide the base member  26  (termed a “port portion” in the publication in question) with a single inlet/outlet port for carrying out both intake and expulsion of liquid medicine. 
         [0077]    Provided that the disengaging means is capable of movement in unison with the pushing member, it may be constituted as a separate member independent of the pushing member. 
         [0078]    Further, whereas in the preceding embodiment the reservoir  28  is fabricated using elastic material, as long as this reservoir  28  has flexibility, it could be fabricated using non-elastic material instead. For example, it would be possible to use pliable resin material shaped into a bellows configuration. 
         [0079]    It is also to be understood that the present invention may be embodied with various other changes, modifications and improvements, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the following claims, while detail illustrations for them are omitted.