Inlet port for a medication infusion pump

<u style="single">BACKGROUND OF THE INVENTION</u>

0001This invention relates generally to an inlet port for use in medication infusion pumps for controlled delivery of a selected medication to a patient over an extended period of time. More particularly, this invention relates to an improved inlet port for use in a medication infusion pump of the constant flow type, for administration of the selected medication to the patient on a substantially constant flow basis. In the preferred form, the medication infusion pump for use with the present invention is adapted for implantation directly into the body of the patient, and for periodic transcutaneous refilling of a medication chamber within the pump.

0002Medication infusion pumps are genenally known in the art for use in delivering a selected medication to a patient including humans and other animals in accordance with an administration schedule which can be preselected or, in some instances, preprogrammed. In recent years, such infusion pumps have been developed in compact form adapted for direct implantation into the body of a patient, to deliver a specific medication such as insulin to the patient in controlled doses over an extended period of time. An implantable infusion pump of this general type includes an internal medication chamber for receiving and storing a supply of the selected medication in liquid form. In some forms, the medication is delivered from the medication chamber into the body of the patient by a miniature pump operated by associated programmable control means for delivering the medication to the patient in selected doses at selected times. For one example of a medication infusion pump of this type, see <patcit id="pcit0001" dnum="US4573994A"><text>U.S. Patent 4,573,994 (Fischell</text></patcit>). In other designs, the medication is maintained within the medication chamber defined by a metal bellows under a positive pressure for delivery as a substantially continuous and preferably constant flow through an appropriate restriction such as a capillary tube. For examples of infusion pumps which use such a positive pressure system with a capillary tube for continuous flow delivery of medication, see <patcit id="pcit0002" dnum="US3731681A"><text>U.S. Patents 3,731,681 (Blackshear</text></patcit>), and <patcit id="pcit0003" dnum="US3951147A"><text>3,951,147 (Tucker</text></patcit>).

0003<patcit id="pcit0004" dnum="US4655765A"><text>US Patent No. 4,655,765</text></patcit> discloses a medication infusion device with an inlet part according to the preamble of claim 1, wherein a septum fitting includes a housing that cooperates with an annular band and a septum to define a cavity. A poppet cooperates with a sealing ring, the annular band and the septum to define an antechamber and to form a seal between the septum and a reservoir. The septum is held in compression between the annular band and a guide to assist resealing of the septum.

0004<patcit id="pcit0005" dnum="US5006115A"><text>US Patent No. 5,006,115</text></patcit> is directed to an implantable medical device having a main body and a port in the main body for receiving a medical instrument percutaneously. A resilient dome is mounted in the device for communicating with the medical instrument and for flexing from a first position to a second position after contact with the medical instrument.

0005<patcit id="pcit0006" dnum="US4557722A"><text>US Patent No. 4,557,722</text></patcit> discloses an inlet port for a medication infusion pump, said inlet port comprising: <ul id="ul0001" list-style="none"><li>a port body having a needle access port formed therein for receiving a refill needle;</li><li>a resilient septum supported on said port body for piercing by the refill needle upon passage of the refill needle through said needle access port;</li><li>a valve seat within said port body;</li><li>a valve member mounted within said port body for movement between a closed position engaging said valve seat and an open position spaced from said valve seat, wherein said valve member is engageable by the refill needle upon passage thereof through said needle access port to move said valve member to the open position.</li></ul>

0006The present invention is directed to an inlet port for a medication infusion pump, such as an implantable flow infusion pump of the constant flow type, wherein the pump components can be arranged and assembled in a highly compact geometry that is compatible with cost-efficient manufacture, and which further provides accurate and reliable delivery of the medication over an extended period of time. An exemplary infusion pump incorporating such an inlet port may provide a substantially optimized and low profile housing configuration suited for implantation into the patient. Moreover, such a pump may incorporate an improved capillary tube and related mounting arrangement in association with a filter of substantially maximized surface area, to result in a capillary tube and filter package that resists clogging. Such resistance to clogging is especially significant when the pump is used to deliver complex protein-based medications, such as insulin, which tend to develop particulate aggregates along fluid flow paths.

<u style="single">SUMMARY OF THE INVENTION</u>

0007In accordance with the present invention, the invention is characterised by: <ul id="ul0002" list-style="none"><li>feedback means carried by said port body and displaced by said valve member upon movement thereof to said open position to indicate proper engagement between said valve member and the refill needle;</li><li>spring means for biasing said valve member normally to said closed position; and</li><li>a plug member adjustably mounted to said port body, said spring means reacting between said valve member and said plug member, and said feedback means being disposed between said valve member and said plug member; wherein said feedback means is separate from said valve member.</li></ul>

0008In a preferred embodiment, said feedback means comprises at least one of a click plate positioned within said port body for over-centre click movement upon displacement thereof by said valve member, tactile feedback means, or an audible feedback device.

0009Preferably the inlet port further includes a filter element carried by said plug member for filtering medication delivered through said port body by said refill needle.

0010Preferably, an improved medication infusion pump for substantially constant flow delivery of a selected medication to a patient usable with the inlet part of the invention comprises a compact housing adapted for implantation directly into the body of a patient including humans and other animals, and includes an inlet port, for example, of the type defined above, to accommodate transcutaneous filling and refilling of a medication chamber within the housing. The medication chamber is subjected to a predetermined and substantially constant pressure by means of a flexible propellant reservoir. The propellant reservoir contains a selected fluid propellant which applies a predetermined pressure to the medication for discharge flow of the medication through a filter of relatively large surface area and a porous restrictive element such as an elongated capillary tube which meters the medication flow to and through an outlet catheter to the patient.

0011The compact housing may comprise a pair of shell-shaped housing elements adapted for assembly and interconnection as by a single weld to define a hollow housing interior. The inlet port is mounted on one of the housing elements and communicates with the housing interior which forms the medication chamber occupying substantially the entire housing internal volume. The flexible propellant reservoir comprises a sealed bag mounted directly within the medication chamber and contains the selected fluid propellant having a vapor pressure so that the propellant is present in a mixed liquid-vapor state to apply a predetermined positive pressure to the medication within the housing. Alternately, the medication chamber may be defined by the flexible bag and the propellant reservoir defined by the residual internal volume of the housing. A bobbin assembly, including the filter and capillary tube, is mounted within the housing at the perimeter thereof, and regulates medication flow from the medication chamber through the filter and capillary tube to the outlet catheter mounted by an outlet port fitting onto the pump housing.

0012A bobbin assembly may be included which comprises a pair of coaxially interfitting bobbin rings assembled in concentric relation, with the filter of annular shape interposed therebetween. An inner bobbin ring is perforated to permit passage of the medication into flow communication with the filter. An outer bobbin ring includes an outlet flow port to which one end of the capillary tube is secured. Accordingly, medication passing through the filter flows through the outlet port for subsequent passage through the capillary tube. The capillary tube is formed preferably from a plastic coated glass tubing with a selected inner diameter size of about 2-10 mils and a length of the order of about 2-750 feet. The capillary tube is wrapped or spooled about the outer bobbin ring, and has the opposite end thereof secured by means of a resilient adapter sleeve to an outlet tube connected in turn via the outlet port fitting to the catheter.

0013As the medication is delivered through the inlet port to fill the medication chamber, the propellant reservoir collapses to a substantially minimal volume, whereby substantially the entire internal volume of the housing is occupied by the medication. This results in an infusion pump construction that has substantially maximized medication capacity with a highly compact pump housing size and shape. Moreover, this construction allows greater freedom as to the shape of the pump housing to include contoured shapes which would be more physiologically and cosmetically suited for patient implantation. As the medication is delivered over time to the patient through the filter and the capillary tube and catheter, the propellant reservoir gradually expands while maintaining the medication under the predetermined constant positive pressure.

0014Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

<u style="single">BRIEF DESCRIPTION OF THE DRAWINGS</u>

0015The accompanying drawings illustrate the invention. In such drawings: <ul id="ul0003" list-style="none"><li><figref idref="f0001">FIGURE 1</figref> is a perspective view illustrating an exemplary medication infusion pump for use with the invention;</li><li><figref idref="f0001">FIGURE 2</figref> is an enlarged transverse vertical seci:ional view taken generally on the line 2-2 of <figref idref="f0001">FIG. 1</figref>, and depicting a medication chamber in a substantially empty condition;</li><li><figref idref="f0001">FIGURE 3</figref> is a further enlarged fragmented sectional view corresponding generally to the encircled region 3 of <figref idref="f0001">FIG. 2</figref>;</li><li><figref idref="f0002">FIGURE 4</figref> is an enlarged transverse vertical sectional view similar to <figref idref="f0001">FIG. 2</figref>, but depicting the medication chamber in a substantially filled condition;</li><li><figref idref="f0003">FIGURE 5</figref> is a horizontal sectional view taken generally on the line 5-5 of <figref idref="f0001">FIG. 2</figref>;</li><li><figref idref="f0003">FIGURE 6</figref> is an enlarged fragmented and partially developed sectional view corresponding generally to the encircled region 6 of <figref idref="f0003">FIG. 5</figref>;</li><li><figref idref="f0004">FIGURE 7</figref> is an enlarged fragmented vertical sectional view taken generally on the line 7-7 of <figref idref="f0001">FIG. 2</figref>, and showing construction details of a preferred inlet port according to the invention;</li><li><figref idref="f0004">FIGURE 8</figref> is a fragmented vertical sectional view similar to <figref idref="f0004">FiG. 7</figref>, and depicting the inlet port in an open condition;</li><li><figref idref="f0004">FIGURE 9</figref> is a top plan view of a click plate for use in the inlet port according to the invention shown in <figref idref="f0004">FIGS. 7 and 8</figref>;</li><li><figref idref="f0005">FIGURE 10</figref> is a perspective view showing a propellant reservoir in a partially manufactured state, for use in the infusion pump usable with the invention;</li><li><figref idref="f0005">FIGURE 11</figref> is a fragmented perspective view depicting further manufacture of the propellant reservoir;</li><li><figref idref="f0005">FIGURE 12</figref> is a perspective view of the completed propellant reservoir;</li><li><figref idref="f0006">FIGURE 13</figref> is an exploded perspective view illustrating components of a bobbin assembly for use with the exemplary pump; and</li><li><figref idref="f0007">FIGURE 14</figref> is an exploded perspective showing installation of the bobbin assembly and propellant reservoir into a housing to form the infusion pump for use with the present invention.</li></ul>

<u style="single">DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT</u>

0016As shown in the exemplary drawings, a medication infusion pump referred to generally in <figref idref="f0001">FIGURE 1</figref> by the reference numeral 10 is provided for use in administering a selected medication to a patient with a substantially constant flow rate over an extended period of time. The infusion pump includes an internal medication chamber 12 (<figref idref="f0002">FIG. 4</figref>) for receiving and storing a supply of the selected medication, wherein this medication chamber is adapted to be refilled at appropriate intervals by means of an inlet port 14. The pump 10 is particularly designed for direct implantation into the body of a patient, and includes an improved capillary tube and filter arrangement for delivering the medication from the chamber 12 through an outlet catheter 16 to the patient at a selected internal administration site. The pump 10 is constructed to provide a substantially optimized medication storage volume in a highly compact and low profile configuration that is designed for cost-efficient assembly and reliable long-term operation.

0017The illustrative medication infusion pump 10 comprises a small and substantially self-contained unit for direct implantation in the body of a patient, wherein the term "patient" will be understood to include humans and other animals. The pump 10 comprises a hermetically sealed pump housing 18 made from a biocompatible material such as titanium or titanium alloy. In the preferred form, the housing 18 includes a pair of interfitting upper and lower shell-shaped housing elements 20 and 22 which are assembled in face-to-face relation to define a hollow housing interior of generally disk-shape having a selected narrow height which can be very small, for example, even as thin as less than about 0.1 inch. The diameter can be of almost any reasonable size, for example, on the order of 1-3 inches. It will be noted, however, that the illustrative disk-shaped housing 18 can be constructed with almost any shape and need not be round or of narrow height. As shown best in <figref idref="f0001">FIGS. 2 and 3</figref>, these housing elements 20 and 22 include peripheral rims shaped for mating engagement, such as by coining the rim of the lower housing element 22 to accommodate reception of the rim of the upper housing element 20. When assembled, the two housing elements 20 and 22 are secured together in a hermetically sealed manner, as by means of a single weld 23, without requiring a separate weld ring insert to position and interconnect the housing components, and further without requiring multiple weld steps associated with a separate weld ring insert. The resultant disk-shaped housing 18 has a compact and low profile circular construction suited for direct implantation into the body of a patient. Alternative compact housing shapes may be used, particularly with respect to contouring the housing for a more optimum physiological and/or cosmetic shape when implanted into the body of a patient.

0018In general terms, the pump housing 18 defines a hollow interior volume occupied substantially and predominantly by the medication chamber 12. A related propellant reservoir 24 is incorporated directly within the medication chamber 12 and functions as will be described in more detail to apply a predetermined positive pressure to the medication. The medication chamber 12 is disposed in flow communication with the inlet port 14 shown located centrally in the upper housing element 20 for receiving the supply of medication therein. The medication chamber 12 is also disposed in flow communication with a bobbin assembly 26 which in this embodiment is mounted within the housing 18 at the perimeter thereof. The bobbin assembly 26 includes a filter 28 of large surface area for filtering the medication as it flows to and through a restrictive element such as an elongated capillary tube 30 coiled within the housing. The capillary tube 30 provides a known restriction to fluid flow, and cooperates with a selected propellant within the propellant reservoir 24 to insure substantially constant flow of the medication through the capillary tube and the outlet catheter 16 to the patient. As the medication in the medication chamber 12 is delivered to the patient, the propellant reservoir 24 expands in volumetric size to maintain the medication under selected and substantially constant pressure.

0019The bobbin assembly 26 is shown in more detail in <figref idref="f0001">FIGS. 3</figref>, <figref idref="f0002">4</figref>, and <figref idref="f0006">13</figref>. As shown, the bobbin assembly 26 comprises a generally annular inner bobbin ring 32 adapted for concentric assembly with a generally annular outer bobbin ring 34, with the filter 28 of annular shape disposed therebetween in a press-fit manner. The assembled bobbin rings 32 and 34 have a diametric size and shape to fit relatively closely with a simple drop-in slide fit into the perimeter of the housing 18, thereby to permit the substantial majority of the housing internal volume to be occupied by the medication chamber 12 with the related propellant reservoir 24 therein. The bobbin rings 32 and 34 desirably include small flats as indicated by arrow 36 in <figref idref="f0003">FIG. 5</figref> to insure assembly thereof in a predetermined rotational alignment, and further to provide a small clearance zone indicated by arrow 38 to accommodate mounting of a side outlet port fitting 40 for connection of the capillary tube 30 to the outlet catheter 16, as will be described in more detail.

0020The inner bobbin ring 32 has a plurality of small perforations 42 formed therein for flow passage of the medication from the medication chamber 12 to and through the filter 28. The filter 28 is provided to remove contaminants and particulate from the liquid medication, wherein such constituents could otherwise obstruct and clog the capillary tube 30 to interfere with proper operation of the infusion pump. While a variety of different filter materials can be used, one preferred filter material is polyethersulfone capable of filtering particles of about 0.2 micron in size. In the preferred construction, the filter 28 is secured to the inner bobbin ring 32 in any suitable manner as by heat staking a small surface thereof in the vicinity of the flat 36 (<figref idref="f0002">FIG. 4</figref>) to the inner bobbin ring. Alternately, the filter 28 may be physically captured between the inner and outer bobbin rings.

0021The outer bobbin ring 34 has an outlet port 44 formed therein for reception of one end of the capillary tube 30, as shown in <figref idref="f0001">FIG. 3</figref>. The outer surface of the outer bobbin ring 34 defines a shallow recess 46 to accommodate spooled wraparound reception of a selected length of the capillary tube 30. An opposite end of the capillary tube 30 is then coupled to a larger diameter outlet tube 47 (<figref idref="f0003">FIG. 6</figref>) by means of a tapered resilient adapter sleeve 49 of a silicone elastomer or the like for press-fit reception and retention of aligned adjacent tubing ends. The outlet tube 47 is connected in turn to the side outlet port fitting 40, shown in <figref idref="f0003">FIGS. 5 and 6</figref> in the form of a small port tube 48 and related clip-on connector 50 of the general type shown and described in <patcit id="pcit0007" dnum="US5527307A"><text>U.S. Patent 5,527,307 (Srisathapat</text></patcit>). The outer bobbin ring 34, with the capillary tube 30 assembled therewith, is assembled with the inner bobbin ring 32 and filter 28 to form a compact ring-shaped subassembly to slide-fit closely within the perimeter of the housing interior. A pair of gasket seals 52 are fitted between the bobbin rings 32 and 34 at the top and bottom thereof, to minimize undesired pockets of medication by confining medication within the bobbin assembly for flow through the filter 28 and capillary tube 30.

0022The diametric size and overall length of the capillary tube 30 is selected, in combination with the design of the propellant reservoir 24 and a fluid propellant therein, to yield a desired and substantially constant flow rate of the medication to the patient. In this regard, white different capillary tube sizes and lengths may be used for different applications, one preferred tube construction for delivery of medication and other therapeutic agents has an inner diameter of about 2-10 mils, and an overall length of about 2-750 feet, with a more preferred construction having an inner diameter of about 3-5 mils and a length of about 40-200 feet. One such capillary tube comprises a polyimide coated glass tubing. This capillary tubing is particularly suited for use in the bobbin assembly for use with the present invention which mounts at the perimeter of the pump housing 18 where the ghss-based tubing is not subjected to sharp bends. A quantity of epoxy 51 (<figref idref="f0001">FIG. 3</figref>) or the like may be used to encase and sealingly retain the capillary tube 30 within the bobbin ring recess 46.

0023The propellant reservoir 24 is mounted directly within the medication chamber 12 within the pump housing 18. In this regard, the exemplary drawings show the propellant reservoir 24 in a preferred form, constructed as a sealed flexible or resilient bag mounted within the housing 18 so that the reservoir bag can act directly upon and apply pressure to the medication. <figref idref="f0005">FIGS. 10-12</figref> show the propellant reservoir bag constructed from a pair of overlying sheets 54 and 56 of flexible plastic film material such as urethane or a selected fluoropolymer sheet or the like chosen for compatibility with the medication to be dispensed. Alternately, the plastic film material may be a sandwich or laminant, or may include a metal sputtered coating, or may be substituted by a metal film material. Other coating formulations such as an organic oxide coating may also be used for the plastic film material to minimize or prevent diffusion therethrough of the fluid propellant. As shown in the illustrative drawings, the upper sheet 54 is formed generally as an inverted cup and also includes a central depression 58 to accommodate the pump inlet port 14 when installed into the pump housing. The overlying sheets 54 and 56 are sealed together as by a heat seam or weld 60, initially leaving a narrow fill port 62 open to permit filling of the bag interior with the selected fluid propellant. After filling, the fill port 62 is also closed and sealed as indicated at 63 (<figref idref="f0005">FIG. 11</figref>) and the sheet margins trimmed to create a short outwardly projecting flange 64 (<figref idref="f0005">FIG. 12</figref>). The filled reservoir 24 is then installed into the housing with a simple drop-in slide fit, and the subsequently installed bobbin assembly 26 overlies and retains the bag flange 64 thereby retaining the propellant reservoir in place within the pump housing.

0024The fluid propellant within the propellant reservoir 24 is selected to apply a substantially constant and predetermined positive pressure to the medication within the medication chamber 12, regardless of the quantity of medication remaining within the chamber 12. While various propellants are available for this purpose, from compounds are available in a range of vapor pressures designed to provide a predetermined and substantially constant pressure to the medication contained within the medication chamber. It will be understood, however, that other liquid-vapor volatile fluids can be used. In a typical application, a mixed state liquid-vapor fluid designed to provide a positive pressure of about 5-50 psi, and preferably about 23-24 psi, at normal body temperature is used.

0025<figref idref="f0004">FIGS. 7-9</figref> show the inlet port 14 in more detail, to include means for positively indicating proper engagement between a refill needle 66 (<figref idref="f0004">FIG. 8</figref>) and the inlet port. This feature is particularly desirable since the infusion pump 10 is refilled transcutaneously, such that the inlet port 14 must be located by palpation through the skin of the patient. By providing a feedback indication of proper engagement between the refill needle 66 and the inlet port 14, correct delivery of the refill medication to the medication chamber 12 is assured, and incorrect delivery of the medication directly from the refill needle 66 to the patient is prevented. This feature is especially desirable in a positive pressure medication reservoir device since the refill medication must be delivered under pressure to the medication chamber.

0026The inlet port 14 comprises a port or valve body 68 adapted for mounting as by welding onto the upper housing element 20 in alignment with a central opening 70. The body 68 defines a conical recess 71 for guided reception of the tip of the refill needle to a narrow access port 72, the lower end of which is closed by a resilient self-sealing septum 74. A cup-shaped valve member 76 is mounted below the septum 74 and is normally retained in sealed contact with a lower surface of the septum and with an annular valve seat 78 by means of a spring 80 reacting between the valve member 76 and a plug 82 threaded into the bottom of the port body 68. When the valve member 76 is engaged by the tip of the refill needle 66 (<figref idref="f0004">FIG. 8</figref>), the valve member is displaced downwardly from the septum 74 and valve seat 78 to open a flow path through side slots 84 in the port body 68 leading to the medication chamber 12. An annular filter element 86 may be provided along this flow path to filter out any particulate in the refill medication. Withdrawal of the refill needle 66 from the inlet port 14 is accompanied by spring-loaded return movement of the valve member 76 to the initial closed position. The threaded advancement of the plug 82 into the port body 68 can variably select and adjust the spring force urging the valve member 76 to the closed position. The plug 82 may conveniently be secured to or otherwise formed as a one-piece component with the annular filter element 86, whereby the combined plug and filter retain the valve seat 78 in place. Importantly, the valve member 76 combines with the septum 74 to provide a redundant closure at the inlet port side of the medication chamber 12.

0027In accordance with one aspect of the invention, an over-center click plate 88 is mounted between the valve member 76 and the plug 82, in a position for depression by the valve member 76 as it moves to the open position. <figref idref="f0004">FIG. 9</figref> shows the click plate 88 in a preferred form to include an upwardly convex dome element 90 supported on four perimeter feet 92. Depression of the click plate 88 results in an audible click sound that can also be felt as a tactile feedback by the person holding the refill needle 66. Thus, the click plate 88 provides a feedback indication, audible and/or tactile, to positively indicate that the refill needle 66 is properly engaged and registered with the inlet port 14.

0028<figref idref="f0007">FIGURE 14</figref> shows the assembly of the infusion pump components, including the major subassemblies thereof to form the constant flow infusion pump 10 for use with the present invention. As shown, the assembled propellant reservoir 24 filled with the selected fluid propellant is dropped with a slide fit into the lower housing element 22. The bobbin assembly 26 is then dropped with a slide fit into the lower housing element 22, in surrounding relation to the propellant reservoir 24, with the outer end of the capillary tube 30 appropriately connected to the side outlet port fitting 40 (not shown in <figref idref="f0007">FIG. 14</figref>). The upper housing element 20, with the inlet port 14 preassembled therewith, is then placed onto the lower housing element 22, and these housing elements 20, 22 are hermetically secured to form the infusion pump. In the assembled state, the gasket seals 52 (<figref idref="f0001">FIG. 3</figref>) on the bobbin assembly 26 engage the upper and lower housing elements 20, 22. In a preferred configuration, a small port 91 may be provided in one of the housing elements 20, 22, as shown in <figref idref="f0001">FIG. 3</figref> with respect to the lower housing element 22, to permit post-assembty hermetic testing of the pump. This port 91 may also be used to permit post-assembly introduction of the epoxy 51 (<figref idref="f0001">FIG. 3</figref>) to retain the capillary tube 30 and further to fill and occupy the residual space between the bobbin assembly 26 and the inside perimeter surface of the housing 18. This port 91 can then be closed and sealed as by welding.

0029In operation, filling of the medication chamber 12 with the selected medication is accompanied by appropriate volumetric collapse of the propellant reservoir 24 to accommodate the medication, as shown in <figref idref="f0002">FIG. 4</figref>. This collapse of the propellant reservoir enables substantially the entire internal volume of the housing, extending throughout the width and height thereof, to be filled with the medication, thereby resulting in a substantially maximized medication capacity restive to the pump housing size. The propellant reservoir and the fluid propellant therein exert the desired substantially constant pressure on the medication to deliver the medication at a substantially constant flow rate through the filter 28 and capillary tube 30 and catheter 16 to the patient. Such medication delivery is accompanied, of course, by gradual increase in the volumetric size of the propellant reservoir as the medication is dispensed. When the medication is entirely dispensed from the pump, the propellant reservoir 24 expands to conform to the shape of and to substantially entirely fill the medication chamber 12.

0030A variety of further modifications and improvements to the inlet port for a medication infusion pump of the present invention will be apparent to those persons skilled in the art. As one example, it will be recognized and understood by persons skilled in the art that the pump inlet port according to the invention can be used with a modified to place the medication within the flexible bag and the propellant within the residual internal volume of the pump housing, with appropriate mounting of the flexible bag in flow communication with the inlet port 14 and the capillary tube 30. Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.