Implantable drug pump with reservoir and fill level sensing system

Abstract

An implantable drug pump (1) with a drug container (2) and a fill level sensing system should be cost-efficient and should provide reliable and accurate results under various operating conditions. According to the invention, this is achieved in that the medicament container (2) comprises a cavity (8) enclosed by a housing (4) and a lid (6) and in which an expandable and collapsible bellows (10) encloses a medicament reservoir (20), the bellows (10) comprising a pleated or folded side wall (12) fixed at the lid (6) and a bellows bottom (14) at a variable distance from the lid (6), wherein a permanent magnet (28) is attached directly or indirectly to the bellows (10) such that the distance of the permanent magnet to the cover (6) varies upon expansion or contraction of the bellows (10), the magnetic field sensor (30, 30 ', 30' ') is fixedly attached to the housing (4) or the cover (6) such that the magnetic field sensor can sense the intensity and / or orientation of the magnetic field caused by the magnet (28), and the fill level sensing system comprises an evaluation unit (32) which determines the intensity and / or orientation of the magnetic field from an output signal of the magnetic field sensor (30, 30', 30 ''), a magnet (28) is attached to the corrugated tube (10) and is correlated to the volume or filling level of the drug reservoir (20), and wherein the magnet (28) is attached to a sheet (42) or rod protruding from the pleats of the side wall (12) of the corrugated tube (10).

Description

Implantable drug pump with storage compartment and fill level sensing system Technical Field

[0001] The field of this invention is an implantable drug pump having at least one reservoir for a drug to be filled. The drug is typically delivered via a catheter to a site in a patient's body to provide treatment. A fill level sensor is used to detect the amount of fluid volume in the reservoir. Background Technology

[0002] US 2018 / 0318503 A1 discloses an implantable drug pump in which a stretchable and retractable bellows encapsulates a drug reservoir. Different types of sensors are described for detecting the position of the bottom of the bellows: strain gauge sensors, light-based sensors, and sound-based sensors. The measured position is then correlated with the volume or fill level of the drug reservoir.

[0003] US 2012 / 259283 A1 illustrates a reservoir fill level detector for a medical drug pump. The reservoir fill level detector includes a coil located in a diaphragm of the pump above the propellant chamber. A recess in the propellant chamber, concentric with the coil, receives a magnetic block that moves in and out of the recess. The magnetic block is mounted on a lever arm. The lever arm is hingedly attached to the upper portion of the propellant chamber. Movement of the bottom portion of the reservoir causes the lever arm to move and change the position of the magnetic block in the recess and relative to the coil. A processor or other circuit connected to the coil measures the current through the coil. The position of the magnetic block will cause a predictable change in the current passing through the coil. The processor may be combined with a memory to record or interpret information to give the reservoir fill level based on the measured current. Thus, the magnetic block acts as the coil core, which, depending on its position, increases or decreases the inductance of the coil due to its permeability. This change in inductance is measured and correlated with the fill level. Summary of the Invention

[0004] The purpose of this invention is to provide an alternative to the aforementioned fill level sensing system in implantable drug pumps that is cost-effective, easy to implement, and provides reliable and accurate results under various operating conditions.

[0005] This objective is achieved by the implantable drug pump according to claim 1.

[0006] Therefore, the present invention provides an implantable drug pump having a drug container and a fill level sensing system. The drug container includes a cavity enclosed by a housing and a cap, wherein an extendable and retractable bellows encloses a drug storage portion. The bellows includes pleated or folded sidewalls fixed to the cap and a bellows bottom at a variable distance from the cap. A permanent magnet is attached directly or indirectly to the bellows such that the distance from the permanent magnet to the cap varies as the bellows extends or retracts. A magnetic field sensor is fixedly attached to the housing or cap such that the magnetic field sensor can sense the strength and / or orientation of a magnetic field induced by the magnet. The fill level sensing system includes an evaluation unit that determines the strength and / or orientation of the magnetic field based on the output signal of the magnetic field sensor and correlates it with the volume or fill level of the drug storage portion. The magnet is attached to a sheet or rod protruding from the pleats of the sidewall of the bellows.

[0007] In contrast to the teachings of US 2012 / 259283 A1, which relies on the influence of a core with magnetic permeability on the inductive properties of a coil, this invention proposes utilizing the long-distance effect of a magnetic field generated by a magnet, such that the strength and / or orientation of the magnetic field can be measured by a suitable sensor and then correlated (or associated) with the volume or filling level of the drug reservoir (e.g., half-full, 10% full, etc.). This can be achieved, for example, through calibrated measurements. Unlike the prior art in which a magnetic probe (which has magnetic permeability but does not necessarily generate its own magnetic field) is immersed in the associated coil, the magnet can be kept at a distance from the magnetic field sensor and can even be separated from it by a material barrier, as long as it does not shield the magnetic field too much. This opens up new constructive possibilities for implementation. Furthermore, surprisingly accurate measurement results can be obtained with minimal energy consumption.

[0008] In a preferred embodiment, the magnetic field sensor is a Hall sensor, an AMR sensor, or a GMR sensor, or any other type of sensor capable of detecting the field strength and / or the angle of the magnetic field relative to a reference direction.

[0009] Preferably, the magnet has the following properties: property parameters tolerance SI unit diameter 1.50±0.05mm length 1.50±0.05mm magnetic intensity 120 minimum mT base region parallel -- no burrs on edges -- In a preferred configuration, the magnet is located inside the drug reservoir. Specifically, the magnet may be attached to the bottom of the bellows, allowing it to directly follow the displacement of the bellows bottom. However, according to the invention, the magnet is attached to a sheet or rod protruding from a fold in the sidewall of the bellows, creating a lever or gear effect where the displacement of the magnet is less than the displacement of the bellows bottom. A similar effect can be achieved when the magnet is attached to a lever arm pivotally mounted between the bellows bottom and the cap. Furthermore, the sheet or lever arm helps bring the magnet closer to the associated magnetic field sensor. When the magnet is located inside the drug reservoir, it is preferable to encapsulate it using a biocompatible sheath (e.g., a titanium sheath). Additionally, the cap advantageously includes a recess for receiving the magnet during the bellows' contracted state, allowing for complete contraction with (near) zero volume of the drug reservoir.

[0010] In a preferred configuration, the magnetic field sensor is located outside the cavity, particularly outside the drug container. Specifically, the magnetic field sensor may be attached to the cap. Alternatively, the magnetic field sensor may be attached to the bottom wall of the housing below the bellows. In variations, the magnetic field sensor may be located inside a sensor chamber within the housing.

[0011] Generally, it is preferable that the housing or cover forms a material barrier between the magnet and the magnetic field sensor. This allows for the separation and sealing of the precision magnetic field sensor from the magnet's position and the drug fluid to be delivered. In this case, the magnetic field sensor is preferably located in an area of ​​the housing or cover with reduced wall thickness (compared to the rest of the housing or cover) to avoid strong attenuation of the magnetic field.

[0012] In order to sense the magnetic field of a magnet in the best possible way and with high intensity, the magnetic field sensor is preferably aligned collinearly with the magnet on the axis of symmetry of the magnetic field.

[0013] In the improved overall concept, two magnetic field sensors are present, configured to cover different ranges of motion of the magnet and provide corresponding output signals to the evaluation unit. Advantageously, in this case, one magnetic field sensor is attached to the cover, and the other to the housing. Attached Figure Description

[0014] Various embodiments of the invention will then be discussed with reference to the accompanying drawings.

[0015] Figure 1 shows a cross-sectional view of the drug container of an implantable drug pump, which has a bellows in an extended state and components of an associated fill level sensor, particularly a magnet and a magnetic field sensor.

[0016] Figure 2 shows the drug container of Figure 1, with the bellows in a contracted state.

[0017] Figures 3 through 11 illustrate further embodiments of implantable drug containers with associated fill level sensors.

[0018] Throughout the description, similar components are identified by the same reference numerals. Detailed Implementation

[0019] Figure 1 shows a cross-sectional view of the drug container 2 of an implantable drug pump 1. The drug pump 1, having the drug container 2, can be implanted into the human or mammalian body to deliver a controlled flow of liquid medication contained in the reservoir of the drug container 2 to a body area of ​​interest, typically via a catheter attached to or integrated with the drug pump 1. This system may also be referred to as an intrathecal drug delivery system. Due to its implantable use, a high level of biocompatibility with all components that come into contact with the body and / or the medication is generally essential.

[0020] The drug container 2 includes a housing 4 with a barrel-shaped recess covered by a cap 6 (particularly a cover plate), such that the housing 4 and the cap 6 enclose a cavity 8. In the example, the cavity 8 has a cubic shape. A bellows 10, having extendable and retractable sidewalls 12 (typically forming a cylindrical encapsulation) comprising multiple zigzag-folded blades and a generally flat bellows bottom 14, is arranged within the cavity 8, such that the cavity 8 is divided into two fluid-separated (sealed against each other) sub-volumes. For this purpose, the sidewalls 12 are attached to and abut against the underside of the cap 6, while the bellows bottom 14 is aligned substantially parallel to the cap 6, at a distance D from the cap 6. This distance D can vary between a minimum and a maximum distance depending on the degree of extension or retraction of the bellows 10. As shown in the example, in the case where the sidewalls 12 of the bellows are recessed into / within the cap 6, the minimum distance can be as low as zero. When the bellows 10 is in its maximum extended state, or when the bottom 14 of the bellows touches the bottom of the barrel-shaped recess in the housing 4, the maximum distance is reached, and a stop is formed on the upper side of the bottom wall 18 of the housing.

[0021] The sub-volume between the bellows 10 and the cap 6 constitutes a drug reservoir 20 with a variable volume, which depends on the extent to which the bellows 10 expands or contracts. Depending on the circumstances, the minimum volume can be as low as zero, while the maximum volume is ultimately limited by the volume of the cavity 8. As mentioned, the drug reservoir 20 is designed to hold and supply a liquid drug or infusion solution, which is typically pressurized and fills the entire sub-volume constituting the drug reservoir 20. The inlet port 22 (particularly an orifice or hole penetrating the cap 6) facilitates the filling of the drug reservoir 20 with drug, and similarly, the outlet port 24 (particularly an orifice or hole penetrating the cap 6) facilitates the extraction of drug from the drug reservoir 20.

[0022] Another sub-volume between the bellows 10 and the housing 4 may form a propellant chamber 26 (see Figure 2), into which pressurized fluid propellant is inserted during assembly (or manufacturing). When the pressure of the propellant is higher than the pressure of the drug in the drug reservoir 20, the bellows 10 is compressed or contracted, and thus the drug is expelled from the outlet port 24.

[0023] Figure 1 shows the bellows 10 in its maximum extended state, where the drug storage section 20 has the largest volume; while Figure 2 shows the bellows 10 in its maximum contracted (or minimum extended) state, where the drug storage section 20 has the smallest volume (here, zero), and the propellant chamber 26 has the largest volume.

[0024] In an alternative embodiment, the cover 6 may be integral with the housing 4, or may be part of the housing 4. This may also be applicable to other embodiments shown in the figures.

[0025] To achieve a high degree of biocompatibility, the bellows 10 is preferably made of titanium or a titanium-based alloy. Furthermore, the shell 4 and / or the cover 6 may be made of titanium or be based on titanium, for example. Grades 23 and 5 are most preferred, but other grades of titanium, such as grades 1-4, are also suitable. These materials exhibit good biocompatibility, excellent fracture toughness, and crack propagation behavior.

[0026] In any case, the displacement or distance D of the bellows bottom 14 relative to the cap 6 is related to the volume of the drug storage section 20 and therefore to the filling level of the implantable drug container 2 (in this case: linearly related). Therefore, in the first embodiment of the invention, the position or displacement or distance of the bellows 10 relative to the fixed cap 6 or housing 4 will be used to detect the volume of the drug storage section 20 and, correspondingly, the amount of drug / fluid inside the drug storage section 20 (generally assuming complete filling).

[0027] For this purpose, a small permanent magnet 28 is mounted / fixed to the bottom 14 of the bellows and moves with it. The magnetic field emitted by the magnet 28 is detected by a magnetic field sensor 30 in a fixed or static position. Changes in the volume inside the bellows 10 will change the distance between the magnet 28 and the magnetic field sensor 30. As a result, the strength and / or angle of the magnetic field reaching the magnetic field sensor 30 also change with the position of the bottom 10 of the bellows and can be correlated with a defined volume of electronics (e.g., through pre-calibration). This evaluation is performed in an electronic evaluation unit 32, which is integrated into the magnetic field sensor 30 or arranged as an external component connected to the magnetic field sensor 30 by wire or wireless means. In Figure 1, the evaluation unit 32 is shown purely schematically, while in other figures, the evaluation unit 32 has been omitted for simplicity.

[0028] In the example of Figure 1, the magnet 28 is fixed to the top side of the bottom 14 of the bellows, which faces the underside of the cover 6 and protrudes slightly upward toward the cover 6. To facilitate the maximum contraction of the bellows 10 toward the zero volume of the drug storage section 20, the underside of the cover 6 advantageously includes a recess 36 to accommodate the magnet 28 during the contracted state of the bellows 10. The recess 36 can be achieved by thinning the wall thickness of the cover 6 in this region.

[0029] In this embodiment, the magnet 28 is positioned within the volume of fluid, i.e., within the drug storage section 20, and may need to be encapsulated in a sleeve 38, preferably made of titanium or a titanium-based alloy, to meet biocompatibility requirements. The encapsulating sleeve 38 containing the magnet 28 can be welded to the bottom 14 of the bellows.

[0030] In this embodiment, the magnetic field sensor 30 is fixed to the top side of the cover 6, i.e., outside the cavity 8 / outside the drug container 2, particularly outside the drug storage section 20. Preferably, the magnetic field sensor 30 is mounted coaxially with the magnetic field generated by the magnet 28. In particular, the magnetic field of the magnet 28 may have an axis of symmetry perpendicular to the plane of the bottom of the bellows 14, and the magnetic field sensor 30 may be located on said axis of symmetry, i.e., vertically aligned above the magnet 28 relative to the bottom plane of the bellows (in the "zenith" direction when viewed from the magnet 28).

[0031] In this embodiment, the cover 6 forms a material barrier between the magnet 28 and the magnetic field sensor 30. Preferably, the magnetic field sensor 30 is positioned in a region of the cover 6 with reduced thickness, such that the material barrier attenuates the magnetic field of the magnet 28 reaching the magnetic field sensor 30 as little as possible, while maintaining the mechanical integrity of the cover 6 on the other hand. This region with reduced wall thickness may be located on the other (outer) side of the (inner) recess 36 for accommodating the magnet 28 during the contraction of the bellows 10, as discussed above.

[0032] For example, the magnetic field sensor 30 may be a Hall sensor, an AMR sensor based on the anisotropic magnetoresistive (AMR) effect, a GMR sensor based on the giant magnetoresistive (GMR) effect, or any other type of sensor capable of detecting the field strength of the magnetic field and / or the angle of the magnetic field relative to a reference direction.

[0033] One advantage of this invention is the small and compact design of the sensing system, which can be integrated into existing products without increasing their size. Furthermore, the associated measurement methods are unaffected by environmental conditions such as changes in temperature or fluid pressure. This makes it a highly reliable measurement system. Depending on the selected magnetic field sensor 30, energy consumption can be very low. These advantages also apply to other embodiments discussed below.

[0034] In the embodiment of Figure 3, the magnetic field sensor 30 is mounted on the lower side of the housing section below the bellows 10, outside the cavity 8. In this embodiment, the bottom wall 18 of the housing 4 below the magnet 28 forms a material barrier between the magnet 28 and the magnetic field sensor 30. Preferably, the magnetic field sensor 30 is positioned in a region of the bottom wall 18 with reduced thickness, such that the attenuation of the magnetic field from the magnet 28 reaching the magnetic field sensor 30 by the material barrier is minimized, while maintaining the mechanical integrity of the housing 4. As in the embodiment of Figure 1, the magnetic field sensor 30 is preferably located on a vertical line intersecting the magnet 28 in a plane passing through the bottom 14 of the bellows.

[0035] The embodiment in Figure 4 is somewhat similar to a combination of the embodiments in Figures 1 and 3, with two magnetic field sensors 30' and 30'' present. The first magnetic field sensor 30' is located on the top side of the cover 6, as described in detail with reference to Figure 1, and the second magnetic field sensor 30'' is located below the bottom wall 18 of the housing 4, as described with reference to Figure 3. In fact, the second magnetic field sensor 30'' is coaxially aligned with the magnet 28 and the first magnetic field sensor 30'.

[0036] The advantage of this extended fill level sensing system is the higher resolution and / or availability of sensor data, especially when the drug reservoir 20 is near its maximum extended state (maximum displacement of magnet 28 from cover 6) or maximum contracted state (maximum displacement of magnet 28 from bottom wall 18 of housing 4). Therefore, when magnet 28 is about to or may exceed the range of the first magnetic field sensor 30', it has already entered the range of the second magnetic field sensor 30'', and vice versa. Thus, the entire range is jointly covered by the two magnetic field sensors 30' and 30''. Accordingly, this sensor configuration is suitable for using bellows 10 with a larger volume, where a larger displacement of the bellows bottom 14 needs to be covered. Within the range or portion of the possible displacement covered by both sensors 30' and 30'', the outputs of the two sensors can be compared to each other for cross-checking and verification / validation. This is done by a common evaluation unit 32 (see Figure 1), to which the two sensors 30' and 30'' are connected.

[0037] In the embodiment of Figure 5, the magnet 28 is attached to a central fold or pleat on the sidewall 12 of the bellows using a titanium sheet 42. The titanium sheet 42 is welded or otherwise fixed to the titanium fold at the outer radius of the bellows 10 and supports the magnet 28. Instead of titanium, another compatible material can be used for the sheet 42. With the magnet 28 thus effectively attached to and coupled to the displacement of the central fold, the displacement of the magnet 28 is reduced in ratio of the number of folds above the central fold to the number of folds below the central fold (compared to the displacement of the bellows bottom 14). For example, in the appropriate location, the maximum displacement of the magnet 28 mounted on the sheet may be only half the maximum displacement of the bellows bottom 14. This prevents the magnet 28 from moving out of the range of the magnetic field sensor 30 aligned with the movement of the magnet 28. This embodiment allows the use of a deeper bellows 14 with a larger volume, but it reduces the resolution of displacement detection of the sensor system, and therefore reduces the resolution of its volume detection.

[0038] In the embodiment of Figure 5, the magnet 28 is located outside the drug storage section 20, but inside the cavity 8, i.e., in the second sub-volume that can form the propellant chamber 26. The magnetic field sensor 30 is located on the top side of the cover 6, which acts as a material barrier between the magnet 28 and the magnetic field sensor 30. In a variation, the magnetic field sensor 30 may be mounted to the underside of the housing wall 4. In another variation, the positions of the magnet 28 and the magnetic field sensor 30 may be reversed. So far, all these combinations can be suitably combined with each other. In yet another variation, the sheet 42 supporting the magnet 28 may be located inside the drug storage section 20, pointing inwards. That is, the magnet 28 is inside the drug storage section 20, and the magnetic field sensor 30 is mounted on the cover 6 or below the bottom wall 18 of the housing 4.

[0039] In the embodiment shown in Figure 6, the magnet 28 is positioned near the edge (i.e., sidewall 12) of the bellows 10, on the bottom 14 of the bellows, i.e., within the drug storage section 20. The magnetic field sensor 30 is positioned within a sensor chamber 44 inside the housing wall, near the sidewall 12 of the bellows, and is perpendicularly aligned to the direction of movement of the bellows 10. The sensor chamber 44 can be sealed against the propellant chamber 26 by a thin partition wall 46. In this embodiment, the magnetic field sensor 30 detects the angle and magnitude of the magnetic field induced by the magnet 28, not just the magnitude.

[0040] In the embodiment of Figure 7, magnet 28 is attached to lever arm 48, which has contact points at the top of drug storage section 20 and the bottom of bellows 10. That is, one end of lever arm 48, for example, is pivotally mounted on the bottom 14 of bellows, and the other end is pivotally mounted on the underside of cap 6, such that in the maximum extended state of bellows 10, lever arm 48 tilts or skews relative to the bottom 14 of bellows, and tilts less towards the maximum contracted state of bellows 10. In this example, magnet 28 is attached near the upper end of lever arm 48, relatively near the magnetic field sensor 30 mounted on the top side of cap 6 above magnet 28. The thickness of cap 6 can be reduced in the effective area of ​​magnet 28, and cap 6 forms a material barrier between magnet 28 and magnetic field sensor 30—where magnet 28 is located within drug storage section 20, i.e., inside drug container 2, and magnetic field sensor 30 is located outside drug container 2. Similar to the embodiment in Figure 5, the magnet 28 mounted on the lever has a smaller displacement than the bottom 14 of the bellows (in this case, linearly). This increases the possible volume range of the drug storage section 20 by limiting the maximum distance between the magnetic field sensor 30 and the magnet 28.

[0041] In a variation of this embodiment, the magnet 28 may be attached near the lower end of the lever arm 48, i.e., near the bottom 14 of the bellows, while the magnetic field sensor 30 is mounted on the lower side of the bottom wall 18 of the housing 4.

[0042] Figure 8 shows a variation of the embodiment in Figure 5. In this embodiment, the magnet 28 is positioned on the other side of the tab, i.e., below the corrugated sheet 42 fixed to the bellows 10. In other words, the magnet 28 is oriented downwards towards the bottom wall 18 of the housing 4. The advantage here is that this orientation allows for different designs of the housing 4 and the cover (e.g., cover 6) while maintaining the same function of the sensor. As in Figure 5, the magnet 28 is preferably located outside the drug storage section 20, but inside the cavity 8, i.e., in the second sub-volume that may constitute the propellant chamber 26. The magnetic field sensor 30 may be located, for example, on the top side of the cover 6 or the housing 4, which acts as a material barrier between the magnet 28 and the magnetic field sensor 30.

[0043] Figure 9 shows a variation of the embodiment in Figure 8 (and subsequently the embodiment in Figure 5). In this embodiment, the magnet tabs (i.e., the sheet 42 holding the magnet 28) are placed on different folds of the bellows 10. This allows for adjustment of the measurement range for different magnet / sensor combinations.

[0044] Figure 10 illustrates an additional variation based on the principles of Figures 5, 8, and 9. In this embodiment, multiple magnets 28 are positioned on the bellows 10, allowing for more detailed and potentially redundant measurements of the displacement of the bellows bottom 14 and thus the volume contained within the drug reservoir 20. More precisely, multiple magnetic tabs (each tab comprising a sheet 42 fixed to a fold of the bellows 10 and a magnet 28) and associated sensors 30 are circumferentially distributed or arranged around the bellows 10. The magnetic tabs may all be fixed to the same fold of the bellows 10, or alternatively to different folds, depending on the desired measurement pattern. The orientation of the magnets 28 may also vary for each of the multiple magnet / sensor units.

[0045] In the event of skewing, tilting, or generally uneven displacement of the bellows 10, the plane in which the bottom 14 of the bellows is located can be generally determined using at least three magnet / sensor units. The corresponding evaluation unit 32 (see also Figure 1) is advantageously programmed or designed to take into account this information regarding the skewing orientation when determining the volume of the drug storage section 20.

[0046] Figure 11 shows an exploded view (top and side view) of an additional variation that can be combined with any of the embodiments of Figures 5, 8, 9, and / or 10. In this embodiment, the magnet 28 is attached to two sheet metal pieces 50, each sheet metal piece 50 having a semi-circular shape with radial arms or protrusions 52 for the magnet 28. The sheet metal pieces are joined to each other (e.g., by welding or gluing) and fitted into one of the pleats of the bellows 10, where they are held in place by tension. This allows for variation in the height position of the magnet 28 for each device.

[0047] Throughout the foregoing description, the term "medicine" is generally understood in a broad sense and can include all kinds of liquid therapeutics, liquid medicines, or infusion solutions.

[0048] Position or orientation indicators (such as "top", "bottom", etc.) are used to conveniently specify or describe certain components or elements by referring to the position and orientation shown in the figure, but do not exclude the possibility of different orientations during use.

[0049] Reference Nomenclature List 1 Drug Pump 2 Drug Container 4 Housing 6 Cover 8 Cavity 10 Bellows 12 Side Wall 14 Bellows Bottom 18 Bottom Wall 20 Drug Storage Section 22 Inlet Port 24 Outlet Port 26 Propellant Chamber 28 Magnet 30, 30', 30'' Magnetic Field Sensor 32 Evaluation Unit 36 ​​Recess 38 Sleeve 42 Sheet 44 Sensor Chamber 46 Separator Wall 48 Lever Arm 50 Sheet Metal Part 52 Protrusion D Distance.

Claims

1. An implantable drug pump (1) having a drug container (2) and a fill level sensing system, the drug container (2) comprising a cavity (8) enclosed by a housing (4) and a cap (6), and within the cavity, a stretchable and retractable bellows (10) encloses a drug storage portion (20), the bellows (10) comprising pleated or folded sidewalls (12) fixed to the cap (6) and a bellows bottom (14) at a variable distance from the cap (6), wherein: • a permanent magnet (28) is directly or indirectly attached to the bellows (10) such that the distance of the permanent magnet from the cap (6) varies with the stretching or retraction of the bellows (10); • a magnetic field sensor (30, 30', 30'') is fixedly attached to the housing (4) or the cover (6) such that the magnetic field sensor is able to sense the strength and / or orientation of the magnetic field induced by the magnet (28), and the fill level sensing system includes an evaluation unit (32) that determines the strength and / or orientation of the magnetic field based on the output signal of the magnetic field sensor (30, 30', 30'') and correlates it with the volume or fill level of the drug storage section (20), and wherein, The magnet (28) is attached to a sheet (42) or rod protruding from the folds of the sidewall (12) of the bellows (10).

2. The implantable drug pump (1) according to claim 1, wherein, The magnetic field sensor (30, 30', 30'') is a Hall sensor, an AMR sensor, or a GMR sensor.

3. The implantable drug pump (1) according to any one of the preceding claims, wherein, The magnet (28) is located inside the drug storage section (20).

4. The implantable drug pump (1) according to any one of the preceding claims, wherein, The magnet (28) is attached to the bottom (14) of the bellows.

5. The implantable drug pump (1) according to any one of the preceding claims, wherein, The cover (6) includes a recess (36) for accommodating the magnet (28) in the retracted state of the bellows (10).

6. The implantable drug pump (1) according to any one of the preceding claims, wherein, The magnetic field sensor (30, 30', 30'') is located outside the cavity (8).

7. The implantable drug pump (1) according to any one of the preceding claims, wherein, The magnetic field sensor (30, 30', 30'') is attached to the cover (6).

8. The implantable drug pump (1) according to any one of claims 1 to 7, wherein, The magnetic field sensor (30, 30', 30'') is located inside the sensor chamber (44) within the housing (4).

9. The implantable drug pump (1) according to any one of claims 1 to 7, wherein, The magnetic field sensor (30, 30', 30'') is attached to the bottom wall (18) of the housing (4) below the bellows (10).

10. The implantable drug pump (1) according to any one of the preceding claims, wherein, The housing (4) or the cover (6) forms a material barrier between the magnet (28) and the magnetic field sensor (30, 30', 30'').

11. The implantable drug pump (1) according to any one of the preceding claims, wherein, The magnetic field sensor (30, 30', 30'') is located in the area of ​​the housing (4) or the cover (6) with reduced wall thickness.

12. The implantable drug pump (1) according to any one of the preceding claims, wherein, Two magnetic field sensors (30', 30'') are configured to cover different ranges of motion of the magnet (28) and provide corresponding output signals to the evaluation unit (32).

13. An implantable drug pump (1) according to any one of the preceding claims, the implantable drug pump (1) having a plurality of magnets (28) distributed in the circumferential direction around the sidewall (12) of the bellows (10) and associated magnetic field sensors (30, 30', 30'').

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