DOSING UNIT REFILLING SCHEDULING

Abstract

A method for managing refilling a first reservoir of an ambulatory infusion system from a first container that stores a first drug and for managing refilling a second reservoir of the ambulatory infusion system out of a second container that stores a second drug is disclosed. The method includes repeatedly and automatically carrying out a filling volume assessment routine, which involves determining the expected infusion of the first drug and the second drug between the present time t.sub.p and the end of an estimation time interval t.sub.f and determining if the first reservoir shall be refilled and/or if the second reservoir shall be refilled at t.sub.p based on the expected infusion of the first drug and the second drug determined in step (a). Ambulatory infusion device control units and ambulatory infusion devices that are configured for carrying out such method are also disclosed.

Claims

1. A method for managing refilling at least one reservoir of an ambulatory infusion system from a first container that stores a first drug and for managing refilling the at least one reservoir of the ambulatory infusion system from a second container that stores a second drug, the method including repeatedly and automatically carrying out a filling volume assessment routine, comprising: (a) determining expected infusion of the first drug and the second drug between the present time t.sub.p and the end of an estimation time interval t.sub.f; (b) based on the expected infusion of the first drug and the second drug determined in step (a), determining at t.sub.p if the at least one reservoir shall be refilled with the first drug and/or if the at least one reservoir shall be refilled with the second drug.

2. The method according to claim 1, wherein the filling volume assessment routine includes determining a first estimated filling volume of the at least one reservoir with the first drug at t.sub.f and determining if the at least one reservoir shall be refilled with the first drug based on the first estimated filling volume.

3. The method according to claim 2, wherein the filling volume assessment routine includes determining that the at least one reservoir shall be refilled with the first drug if the first estimated refilling volume is below a first filling volume threshold.

4. The method according to claim 2, wherein the filling volume assessment routine includes determining the first estimated filling volume by subtracting a first infusion estimator from a first filling volume of the first drug in the at least one reservoir at t.sub.p, wherein the first infusion estimator is an estimator for the amount of the first drug that is expected to be infused between t.sub.p and t.sub.f.

5. The method according to claim 4, wherein the method includes computing a set of first standard infusion estimators, with each first standard infusion estimator being an estimator for an amount of first drug that is expected to be infused in an estimation time interval beginning at an associated pre-determined time of day, and storing the set of first standard infusion estimators in a memory, wherein the filling volume assessment routine includes retrieving from the memory the first standard infusion estimator that is associated with the time of day corresponding to t.sub.p.

6. The method according to claim 2, wherein determining if the at least one reservoir shall be refilled with the first drug is based, at least in part, on a pre-determined first basal infusion schedule for the first drug.

7. The method according to claim 2, wherein determining if the at least one reservoir shall be refilled with the first drug is based, at least in part, on an expected amount of on-demand bolus infusion for the first drug between t.sub.p and t.sub.f.

8. The method according to claim 2, wherein the method includes computing a set of second standard infusion estimators, with each second standard infusion estimator being an estimator for an amount of second drug that is expected to be infused in an estimation time interval beginning at an associated pre-determined time of day, and storing the set of second standard infusion estimators in a memory, wherein the filling volume assessment routine includes retrieving from the memory the second standard infusion estimator that is associated with the time of day corresponding to t.sub.p.

9. The method according to claim 1, wherein the at least one reservoir comprises separate first and second reservoirs.

10. The method according to claim 1, wherein the at least one reservoir comprises a single common reservoir configured to alternately receive the first drug and the second drug.

11. The method according to claim 10, wherein the filling volume assessment routine includes determining that the common reservoir shall be refilled with the second drug if an infusion of the second drug is expected to occur between t.sub.p and t.sub.f and prior to a next following on-demand bolus infusion of the first drug.

12. A refilling scheduling unit configured to carry out the method according to claim 1.

13. A non-transient computer readable medium having stored thereon computer program code configured to direct a processor to execute a method according to claim 1 and/or to act as a refilling scheduling unit and/or as an ambulatory infusion device controller.

14. An ambulatory infusion device controller, comprising: a first valve controller configured to control actuation of a first valve actuator to switch a first valve between a filling state and an alternative dosing state; a second valve controller configured to control actuation of a second valve actuator to switch a second valve between a filling state and an alternative dosing state; a first reservoir actuator controller configured to control operation of a first reservoir actuator to operate in a filling mode and to increase a fluidic volume of a first reservoir in the filling mode, and to alternatively operate in a dosing mode and to decrease the fluidic volume of the first reservoir in the dosing mode; a second reservoir actuator controller configured to control operation of a second reservoir actuator to operate in a filling mode and to increase a fluidic volume of a second reservoir in the filling mode, and to alternatively operate in a dosing mode and to decrease the fluidic volume of the second reservoir in the dosing mode; a refilling scheduling unit configured to operate in parallel with the first reservoir actuator controller and the second actuator controller in the dosing mode; wherein the ambulatory infusion device controller is further configured to control execution of a first reservoir refilling procedure comprising: (i) controlling the first valve actuator to switch the first valve into the filling state; (ii) controlling the first reservoir actuator to increase the fluidic volume of the first reservoir; and (iii) controlling the first valve actuator to switch the first valve into the dosing state, and wherein the ambulatory infusion device control unit is further configured to control execution of a second reservoir refilling procedure, comprising: (i) controlling the second valve actuator to switch the second valve into the filling state; (ii) controlling the second reservoir actuator to increase the fluidic volume of the second reservoir; and (iii) controlling the second valve actuator to switch the second valve into the dosing state.

15. An ambulatory infusion device controller configured to control operation of an ambulatory infusion device, the ambulatory infusion device controller comprising: a valve controller configured to control actuation of a valve actuator to switch a valve unit between a first filling state, an alternative second filling state and an alternative dosing state; a reservoir actuator controller configured to control operation of a reservoir actuator to operate in a filling mode and to increase a fluidic volume of a common reservoir in the filling mode, and to alternatively operate in a dosing mode and to decrease the fluidic volume of the common reservoir in the dosing mode; a refilling scheduling unit configured to operate in parallel with the reservoir actuator in the dosing mode; wherein the ambulatory infusion device controller is further configured, if it is determined that the first reservoir shall be refilled, to control execution of a first reservoir refilling procedure, the first reservoir refilling procedure comprising: (i)(a) controlling the valve actuator to switch the valve into the first filling state; (ii)(a) controlling the reservoir actuator to increase the fluidic volume of the common reservoir; (iii)(a) controlling the valve actuator to switch the valve into the dosing state, and; wherein the ambulatory infusion device controller is further configured, if it is determined that the second reservoir shall be refilled, to control execution of a second reservoir refilling procedure comprising: (i)(b) controlling the valve actuator to switch the valve into the second filling state; (ii)(b) controlling the reservoir actuator to increase the fluidic volume of the common reservoir; (iii)(b) controlling the valve actuator to switch the valve into the dosing state.

16. The ambulatory infusion device controller according to claim 15, wherein the first reservoir refilling routine includes, prior to step (i)(a), a first emptying sequence (i)(a) controlling the valve actuator to switch the valve into the second filling state; (ii)(a) controlling the reservoir actuator to decease the fluidic of the common reservoir to a minimum volume; and/or wherein the second reservoir refilling routine includes, prior to step (ib), a second emptying sequence comprising: (i)(b) controlling the valve actuator to switch the valve into the first filling state; (ii)(b) controlling the reservoir actuator to decease the fluidic of the common reservoir to a minimum volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0103] The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0104] FIG. 1 shows major components of an ambulatory infusion system in a simplified functional view;

[0105] FIG. 2 shows an operational flow in accordance with the present disclosure;

[0106] FIG. 3 shows a further operational flow of a refilling scheduling method in accordance with the present disclosure.

DESCRIPTION

[0107] The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

[0108] In the following, reference is first made to FIG. 1. FIG. 1 shows a dosing unit 100, an ambulatory infusion device 200, and a first drug reservoir 300 (also referred to as first container) and a second drug reservoir 300 (also referred to as second container). In an example that is also assumed in the following, the first container 300 stores insulin and the second container 300 stores glucagon, both in the form of a liquid formulation. It is to be noted that only those structural and functional units are shown that are of particular relevance in the context of the present disclosure.

[0109] The dosing unit 100 includes a metering pump unit 110, including a dosing cylinder with a bore and a piston (elements not separately referenced) as described above in the general description. In a proximal front wall of the dosing cylinder, a bore is arranged as fluidic port that couples to the pump port 127a. The dosing unit further includes a valve unit 120 that may alternatively be in a first filling state, 120b, a second filling state 120b, or a dosing state 120a. During operation, the valve unit 120 is repeatedly switched between those states as explained further below in more detail. The first container 300 is fluidically coupled to the valve unit 120 via a first filling port 127b and the second container 300 is fluidically coupled to the valve unit 120 via a second filling port 127b that is different from the first filling port 127b. The patient 900 is fluidically coupled to the valve unit via a dosing port 127c and infusion site interface 890, which may optionally be integral with a fluidic line, e.g., a catheter. The dosing unit 100 further includes a valve driver coupler 125 for switching the valve unit 120 between the first filling state 120b, the second filling state 120b, and the dosing state 120a. Similarly, the dosing unit 100 includes a pump driver coupler 115 for moving the piston of the pump unit 110 linearly inside the dosing cylinder. In an exemplary embodiment, the maximum filling volume of the dosing cylinder is 7 IU (International Units) of a liquid insulin formulation with concentration U100, respectively 70 microliter.

[0110] With respect to the valve unit 120, it is further noted that FIG. 1 only shows the states 120a, 120b, 120b where either of the filling ports 127b, 127b or the dosing port 127c is coupled to the pump port 127a. In a further optional intermediate state, however, all ports 127a, 127b, 127b, 127c may be closed, resulting in fluidic isolation.

[0111] The ambulatory infusion device includes a pump drive 217 that is coupled to a pump drive coupler 215 as well as a valve drive 227 that is coupled to a valve drive coupler 225. The pump drive 217 and the valve drive 227 are powered and controlled by an electronic ambulatory infusion device control unit 250 that is typically based on one or more microcontrollers and/or microprocessors.

[0112] The dosing cylinder and the piston form in combination a common reservoir, while the drug reservoir 300 forms a first container and the second drug reservoir 300 forms a second container as explained above. The first container 300 and the second container 300 may be realized by a cylindrical cartridge with sealing displaceable cartridge piston, or may be a fully or partly flexible container, such as a pouch. The first container 300 and the second container 300 may further be of identical or different design. Further, either of them may be provided readily filled by a manufacturer, or may be user-filled. The ambulatory infusion device control unit 250 further includes a reservoir actuator control unit (not separately referenced) that controls operation of the pump drive 217 as reservoir actuator. Further, the ambulatory infusion device control unit 250 includes a valve actuator control unit (not separately referenced) that controls operation of the valve drive 227 as valve actuator. The ambulatory infusion device control unit 250 further includes a refilling scheduling unit 251 in accordance with the present disclosure, operation of which is further explained in more detail below.

[0113] It is noted that the containers 300, 300 and the dosing unit 100 are shown as distinct from the ambulatory infusion device 200. They may be and typically are, however, in an operational configuration mechanically coupled to the ambulatory infusion device 200 to form a common, compact unit, and/or may be inserted into corresponding compartments of the ambulatory infusion device housing. Further, the dosing unit 100 and either or both of the containers 300, 300 may be realized as common unit in some embodiments.

[0114] Favorably, the ambulatory infusion device is designed as patch device that is designed to be, in a situation of use, directly attached to the body of the patient 900, e.g., the abdomen as generally known in the art. This has the advantage that the fluidic volume of the infusion site interface 890 is small and preferably negligible. A negligible fluidic volume of the infusion site interface is favorable in view of the required switching between the infusion of insulin and glucagon, or, more generally, the first and second drug. If the fluidic volume is not negligible, it may be considered as explained further below.

[0115] In the following, reference is additionally made to FIG. 2, illustrating an exemplary method in accordance with the present disclosure. The method starts in step S1 where a new ambulatory infusion device is provided to a user, e.g., a Person with Diabetes (PwD). The ambulatory infusion device is designed to be used in combination with a first and second container and a common reservoir (referred to as reservoir) as explained before. It is noted that the methods that are illustrated in FIGS. 2, 3 are based on a setup with an ambulatory infusion device 200 and a dosing unit 100 and its components as illustrated in FIG. 1 and explained before.

[0116] In subsequent parameter setting step S2, the ambulatory infusion device is prepared and initialized for use by the user. This in particular includes the programming of the basal administration schedule for insulin as first drug, or a number of basal administration schedules, e.g., for working days and for weekends, as explained before. In many state-of-the-art systems, the ambulatory infusion device comprises or is adapted to operatively couple to a bolus recommendation system. A bolus recommendation system is designed to compute and propose to the user bolus volumes of drug boli, in particular insulin boli, that are appropriate for covering an amount of food intake, in particular carbohydrate intake, and/or for lowering undesirably raised blood glucose values. The computation depends on the amount and potentially type of food and/or the blood glucose value, using a number of patient-specific bolus computation parameters that are also set respectively programmed in step S2. If the ambulatory infusion device that has been provided in step S1 is a replacement device for a previously used device, step S2 may comprise or consist of retrieving the one or more basal administration schedules and bolus computation parameters from the previously used device respectively from a data file storing such parameters.

[0117] In subsequent maintenance step S3, a dosing unit with a reservoir as well as a first container and a secondary container are inserted into the ambulatory infusion device and coupled with an infusion cannula directly or via infusion tubing. Further, additional steps that are required in the context of exchanging the dosing unit and/or the reservoir are carried out, such as priming. Here it is assumed that the both containers and the dosing unit with the reservoir are generally exchanged along with each other, e.g., every few days up to every few weeks, in dependence of the user's individual requirements. The dosing unit and the containers may also be formed as common integral unit. Alternatively, however, they may be structurally separate and also exchanged separate from each other. Further, glucagon as second drug may be infused in substantially lower volumes as compared to the first drug insulin. Therefore, it may be foreseeable to replace the first and second container independent from each other.

[0118] In subsequent step S4, standard infusion estimators are computed for use during regular operation. The standard infusion estimators include a set of set of first standard infusion estimators for insulin and a set of second standard infusion estimators for glucagon. The set of first standard infusion estimators includes a set of standard basal infusion estimators and a set of standard bolus infusion estimators. Since glucagon as second drug is only infused in the form of boli, the set of second standard infusion estimators only considers bolus infusion. By way of example, the estimation time interval is pre-determined as two hours, and a standard bolus estimator and a standard basal estimator for insulin as well as a standard bolus estimator for glucagon are computed for specific times of day with an interval of 10 minutes, that is, for 0:00 (midnight), 0:10, 0:20, 0:30, 0:40, 0:50, 1:00 (1 am), and so forth. The set of standard basal infusion estimators for insulin is computed based on the basal infusion schedule. Alternatively to a computation based on the basal infusion schedule as programmed, the basal infusion estimators may be computed based on actual past basal insulin infusion as stored in a history memory. This approach has the advantage that typical temporary modifications that occurred in the past are also taken into account. The set of standard bolus infusion estimators for insulin is computed based on a history of actual past bolus infusions that is stored in a history memory of the ambulatory infusion device itself and/or an external device, such as a remote controller or diabetes management device. For the computation, the data are retrieved from the history memory (Step S4). For each time of day as start time for which the computation is carried out, the corresponding bolus infusion estimator is computed as, e.g., 80.sup.th percentile, as explained above. The computation is, e.g., carried out based on a number of, e.g., three or seven past days. The standard bolus infusion estimators for glucagon are computed according to the same principles as the standard bolus infusion estimators for insulin.

[0119] Subsequent to steps S4, S4, regular drug infusion is carried out. As background process, a filling volume assessment procedure is repeatedly and automatically carried out (Steps S5, S5), as explained further below in more detail.

[0120] If, during regular operation, either of the containers becomes empty, the operational flow proceeds with step S6 where infusion is stopped and a corresponding message is provided. From step S6, the operational flow returns to the maintenance routine S3. Favorably, one or more warnings are provided well before the container is actually empty, allowing the user to go to the maintenance step S3 and exchange the dosing unit and the containers at a convenient point in time.

[0121] In the following, reference is additionally made to FIG. 3, showing the operational flow of steps associated with the scheduling of the refilling, as well as a further related step during regular operation of the ambulatory infusion device.

[0122] In step S10, regular operation of the ambulatory infusion device is started for infusion of insulin as first drug, i.e., the ambulatory infusion device is operated to autonomously infuse insulin according to the basal administration schedule and additional insulin boli on demand.

[0123] In subsequent step S11, the present point in time is set as time for carrying out a filling volume assessment. In subsequent step S12, the estimated filling volume of the common reservoir is determined, with the common reservoir serving as first reservoir.

[0124] In embodiments where sets of standard bolus infusion estimators for insulin and glucagon and standard basal infusion estimators for the insulin infusion have been computed in advance, step S12 comprises retrieving the standard basal infusion estimator and the standard bolus estimators that are associated with the present point in time and determining the estimated filling volume of the reservoir by subtracting the standard basal estimator and the standard bolus estimator for insulin from the current filling volume of the reservoir. In alternative embodiments where no standard infusion estimators have been computed in advance, the estimated filling volume of the reservoir may be computed in step S12 as explained in the general description, using the present point in time as the start point and the present point in time plus the estimation time interval as the end time.

[0125] In subsequent step S13, it is determined whether any temporary modifications of the insulin infusion are active. Data regarding such temporary modification may be retrieved (step S5) from a continuous glucose measurement device or continuous glucose measurement unit, and/or from a memory of the ambulatory infusion device which stores information regarding temporary modifications. If such modification is active, step S13 further includes modifying or updating the estimated filling volume of the reservoir accordingly.

[0126] In subsequent step S13, it is determined whether the infusion of a glucagon bolus is expected to occur in the estimation time interval between the present point in time and the future point in time and the operational flow branches in dependence of the result. If no infusion of a glucagon bolus is expected, the operational flow proceeds with step S14 as explained further below.

[0127] If the infusion of a glucagon bolus is expected, the operational flow proceeds with step S101. In step S101, it is determined whether the infusion of the glucagon bolus is expected to occur before the next following infusion of an insulin bolus, or, alternatively, if the infusion of a glucagon bolus is expected before the next following insulin infusion, and the operational flow branches in dependence of the result. In a further general implementation of step S13 it is determined whether the next following infusion is expected to be an insulin or a glucagon infusion.

[0128] If it is determined in step S101 that the next following insulin infusion or insulin bolus infusion is expected to occur before the actual point in time of the glucagon infusion, the operational flow again proceeds with step S14. Otherwise, the operational flow proceeds with step S102. In step S102, a second emptying sequence is first carried out. In the second emptying sequence, the valve actuator is controlled to switch the valve unit into the first filling state, thereby fluidically coupling the dosing cylinder as common reservoir with the first container, followed by controlling the reservoir actuator to decease the fluidic volume of the dosing cylinder as common reservoir to a minimum volume. Thereby, the dosing cylinder is emptied of insulin. In embodiments where the fluidic volume of the infusion site interface 890 is not negligible, the second emptying sequence may include, prior to switching the valve unit form the dosing state into the first filling state, increasing the fluidic volume of the reservoir by withdrawing the piston in the dosing cylinder by the fluidic volume of the infusion site interface, thereby sucking the insulin that is present in the infusion site interface into the dosing cylinder respectively reservoir.

[0129] In subsequent step S103, the valve unit is controlled to switch the valve unit into the second filling state, thereby fluidically coupling the dosing cylinder as common reservoir with the second container that comprises glucagon. Further in step S103, the reservoir actuator is controlled to increase the fluidic volume of the dosing cylinder as reservoir, thereby filling the dosing cylinder with glucagon. The filling volume of glucagon favorably corresponds to the amount that is expected to be infused based on the bolus infusion estimator for glucagon.

[0130] In subsequent step S104, a specific user command for the glucagon infusion is awaited. Further in step S104, upon the glucagon infusion being commanded by the user, the valve actuator is controlled to switch the valve unit into the dosing state, followed by controlling the reservoir actuator to decrease the filling volume of the dosing cylinder as reservoir, thereby infusing the glucagon. Since the dosing cylinder has been filled with glucagon beforehand, the glucagon infusion can start immediately upon being commanded, which is particularly favorable. It is noted that the step of switching the valve unit into the dosing state could alternatively be done in step S103 after filling the dosing cylinder with glucagon. At the end of the glucagon infusion, the dosing cylinder is empty, i.e., the fluidic volume of the reservoir is minimum respectively zero or at least negligible. Subsequently, the operational flow returns to step S11 as explained before.

[0131] In embodiments where the ambulatory infusion device is operatively coupled with a continuous glucose sensor to operate as closed loop system, awaiting a specific user command for the glucagon infusion may not be required.

[0132] In a practical implementation, the sequence of steps S102, S013 and S104 that is directly related to the glucagon infusion as second drug may include a number of further steps and branches that are not reflected in FIG. 3 for the sake of clarity and conciseness. In particular, a situation may occur where a glucagon infusion that is expected based on the infusion history is in fact not carried out. In such situation, the operational flow may provide for forcing the glucagon back into the second container. Further, a situation may occur where the user decides to infuse glucagon, but with a different bolus volume than expected. If the actual bolus volume is smaller than expected, the dosing cylinder is not empty at the end of the glucagon infusion. In this case, step S104 may include switching the valve unit into the second filling state and forcing the remaining glucagon back into the second container. If the actually commanded bolus volume is larger than expected, the current filling volume may be infused in a first step, followed by filling the dosing cylinder with the remaining volume subsequently in a second step, or the filling volume of the dosing cylinder may first be increased to the desired volume and the glucagon infusion may be carried out in a single step.

[0133] In embodiments where the fluidic volume of the infusion site interface 890 is not negligible, step S104 may include, following the glucagon infusion, increasing the fluidic volume of the dosing cylinder as reservoir by withdrawing the piston in the dosing cylinder by the fluidic volume of the infusion site interface, thereby sucking the glucagon that is present in the infusion site interface into the dosing cylinder respectively reservoir, followed by switching the valve unit into the second filling state and forcing the glucagon into the second container.

[0134] In step S14, the operational flow branches in dependence of the estimated filling volume with insulin as the first drug.

[0135] If the estimated filling volume at the future estimation point in time is positive, the operational flow proceeds with step S15. Here it is accordingly assumed that the reservoir will not become empty within the estimation time interval. In this case, optional steps S15, S16, S17 are carried out.

[0136] In step S15, the time that has lapsed since the last refilling of the reservoir is assessed by way of comparison with a pre-determined back-dosing time interval of, e.g., 12 hours, and the operational flow branches in dependence of the result. If a refilling has been carried out within the back-dosing time interval, the operational flow proceeds with step S16 where no action is required. Otherwise, a back-dosing sequence is carried out in step S17.

[0137] In the back-dosing sequence, the valve actuator is controlled to switch from the dosing state into the filling state. Subsequently, the reservoir actuator is, while in the dosing mode, controlled to decrease the fluidic volume of the reservoir by a small back-dosing volume. Subsequently, the valve actuator is controlled to switch back from the filling state into the dosing state. By decreasing the fluidic volume of the reservoir, an amount of drug that corresponds to the back-dosing volume is forced from the reservoir into the container. For the container being a glass or plastic cartridge with a cartridge piston that is sealing and movable arranged in a glass cartridge body, this is associated with a forced movement of the cartridge piston inside the cartridge body against its regular movement direction for emptying the cartridge, the forced piston movement being associated with a pushing force that is exerted onto the cartridge by the drug. In this way, a breakaway force between cartridge piston and cartridge body that typically builds up if the piston is not moved for some time, is overcome. Such breakaway force may be considerable and well above a pulling force that may be fluidically exerted on the piston by drawing liquid out of the cartridge. It is noted that the method steps associated with the back-dosing may also be independently implemented as piston sticking prevention method.

[0138] After either of step S16 or step S17, the operational flow proceeds with step S22 as explained further below.

[0139] In alternative embodiments where the breakaway force is particularly low, or in embodiments where another type of container, such as a pouch, is used, steps S15, S16, and S17 may not be required.

[0140] If the estimated filling volume at the end time is negative, the operational flow proceeds, following step S14, with step S18. In step S18, it is determined whether a next following bolus infusion is expected to occur only after a time interval as defined by a bolus timeout threshold from the present point in time. The bolus timeout threshold may be 20 min in a specific example, but longer or shorter values may be used as well. In the affirmative case, the operational flow proceeds with step S19 where it is determined that no action is presently required. Otherwise, the operational flow proceeds with step S20 where it is determined whether the expected amount of the next following bolus exceeds a bolus volume threshold. Favorably, the bolus volume threshold is dynamically set to the present filling volume of the reservoir. In the negative case, the operational flow also proceeds with step S19. Otherwise, the operational flow proceeds with step S21 where a refilling of the reservoir with insulin is initiated.

[0141] After carrying out either of step S19 or step S21, the operational flow proceeds with step S22. In step S22, the operational flow pauses until the present point in time corresponds to the time for the next subsequent execution of the filling volume assessment routine. In subsequent step S23, it is determined whether the container is empty. In the affirmative case, the operational flow proceeds with step S6, where the algorithm terminates and a replacement routine for the container and optionally the dosing unit with the reservoir is initiated. In the negative case, the operational flow returns to step S11 for the next execution of the filling volume assessment routine.

[0142] It is noted that, like steps S15, S16 S17, the steps S18, S19 S20 are optional. Via steps S18, S19, an otherwise initiated refilling is avoided in situations where it may in fact be unnecessary due to typical variability in drug infusion, as explained in the general description. Via additional step S20, a refilling is avoided at the present point in time in situations where the next expected on-demand bolus may still be infused without prior refilling.

[0143] While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.