Abstract:
A mixing system ( 1 ) adapted to allow first contents of a first container ( 2 ) and second contents of a second container ( 3 ) to mix to form a material. The mixed material is retrieved to a syringe ( 20 ) without being foamed. The mixing system ( 1 ) comprises a transfer unit ( 5 ) which is adapted to receive the first container ( 2 ) at a first port ( 11 ), the second container ( 3 ) at a second port ( 12 ) and the syringe ( 20 ) at a third port ( 13 ). The transfer unit ( 5 ) further houses a number of fluid pathways ( 14, 15, 16 ) interconnecting the three ports ( 11, 12, 13 ) as well as a number of flow control members ( 17, 18, 19, 22 ) for controlling fluid flow between the containers ( 2, 3 ) and the syringe ( 20 ). At least one of the flow control members ( 17, 18, 19, 22 ) allows a user to switch between two states of fluid flow, one in which fluid flow is enabled between the first port ( 11 ) and the third port ( 13 ) as well as between the third port ( 13 ) and the second port ( 12 ), and one in which fluid flow is enabled between the second port ( 12 ) and the third port ( 13 ). The invention also relates to a transfer unit comprising first and second ports for receiving first and second containers, respectively, a third port for coupling to a syringe, a number of fluid pathways interconnecting the ports, at least one flow control member which allows a user to switch between two states of fluid flow, and a locking means to ensure that the at least one flow control member can only be manipulated when a syringe is coupled to the third port.

Description:
[0001]    The present invention relates to the mixing of substances, e.g. of an active powdered drug and a solvent or diluent, for the preparation of a product that can be administered to the body by e.g. injection or infusion. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known in the art that the storage life of certain injectable substances, such as glucagon, is increased when the substance is stored in a powdered state. Lyophilization is one way of producing a powdered substance from a liquid based material. It involves a rapid freezing of the material at a very low temperature followed by a rapid dehydration by sublimation in a high vacuum. The resulting lyophilized substance is typically stored in a glass vial or cartridge which is closed by a cap, such as a rubber stopper or septum. 
         [0003]    It is necessary to reconstitute the powdered or solid substance prior to administration. This is accomplished by mixing the powdered substance with a suitable diluent or liquid. Reconstitution is traditionally performed using a syringe with a needle to withdraw the diluent from one separate vial and inject it into another separate vial containing the powdered compound, whereupon the latter vial is shaken or swirled to thoroughly mix the two constituents. The syringe with needle is then used to withdraw from this vial the desired amount of reconstituted drug to be injected into the patient. Because two separate containers are used, the person reconstituting the compound must be certain to mix the correct amounts such that a proper concentration of the mixture results. 
         [0004]    When a syringe is used to mix the diluent and the drug, an exact diluent to drug ratio is difficult to obtain. This brings about some uncertainty regarding the exact concentration of administered drug. 
         [0005]    Moreover, because the diluent and the compound are in separate, sterilized containers, and the diluent is manually withdrawn from the diluent container via a syringe with a needle, and the syringe is subsequently moved from the diluent container to the compound container for injection of the diluent into the compound container, both sterility and safety are in risk of being compromised. 
         [0006]    Because of an increased use of powdered compounds or lyophilized drugs it is desirable to provide both professionals and non-professionals with a simple and reliable system that facilitates preparation of an accurate dosage of a mixed product, e.g. a reconstituted compound. 
         [0007]    In addition, it is desirable to provide a system that can reconstitute a lyophilized drug without potential hazards to the user while maintaining sterility throughout the process. 
         [0008]    U.S. Pat. No. 5,466,220 discloses a mixing device comprising a base on which a syringe and two vials are mounted together with a T-shaped connector piece. Retainers hold the two vials in place at a predetermined spacing from their respective connectors prior to operation of the device. The device is kept within a protective sterile packaging until the vials are pushed into their respective connectors allegedly providing a system that is sealed during the entire reconstitution process. 
         [0009]    U.S. Pat. No. 6,364,865 discloses different embodiments of medication delivery systems and transfer systems for forming a solution from constituents from a set of vials respectively containing a lyophilized compound and a diluent. 
         [0010]    Sometimes a desired dose of a drug solution exceeds the amount corresponding to the drug contained in a single set of vials. In this case the total dose must be composed using lyophilized drug from two or more vial sets, the number of vial sets corresponding to the desired dose. This may, e.g., be done by sequentially applying a solvent liquid to each of the vials and retrieving the reconstituted drug to one common reservoir or syringe. When the drug of all of the vials has been reconstituted in this manner, the total dose may be administered to the person from the common reservoir or syringe. Reconstituting lyophilized drug from two or more vials in this manner is, however, relatively time consuming. Furthermore, there is a risk of contamination of the drug due to the number of times a free opening will be exposed to free air or dirt. 
         [0011]    It is therefore desirable to provide a mixing system which facilitates mixing a dose using powdered drug from two or more vials, also known as pooling, and which reduces the risk of contamination of the resulting drug. 
         [0012]    WO 2007/122209 discloses a transfer system comprising a container unit holding two containers and a transfer unit adapted to be coupled to the container unit for enabling a mixing of the contents of the two containers, wherein a pressure generator, such as a syringe, is used to force the contents of the one container to move to the other container via a channel in the transfer unit fluidly connecting the two containers. 
         [0013]    When emptying the container containing the final mixed product the influence of included air should be minimised in order to avoid foaming of the drug. Two factors which may contribute to the generation of foam in a system as described in WO 2007/122209 are the flow rate of the drug solution when transferred from the container to the syringe and air that is potentially aspired from other parts of the system such as the solvent container. 
         [0014]    It is desirable to provide a mixing system which substantially eliminates the issue of foaming. Avoiding foaming is highly important for several kinds of drugs, in particular drugs that must be given intravenously, such as recombinant factor products for the treatment of haemophilia patients. 
       SUMMARY OF THE INVENTION 
       [0015]    Having regard to the above mentioned problems and deficiencies, it is an object of the present invention to provide a mixing device, which is simple and efficient for users to operate and which provides for a sterile preparation of an accurate dosage of administrable drug. 
         [0016]    A further object of the invention is to provide a mixing system for reconstituting a powdered drug, which substantially eliminates foaming of the final reconstituted product. 
         [0017]    An even further object of the invention is to provide a mixing system that is simple and cost efficient to produce. 
         [0018]    In the disclosure of the present invention, aspects and embodiments will be described which will address one or more of the above objects or which will address objects apparent from the below disclosure as well as from the description of exemplary embodiments. 
         [0019]    In a first aspect of the invention a medical mixing system is provided comprising a first container containing first contents, a second container containing second contents, and a transfer unit. The transfer unit comprises a first port adapted to receive the first container, a second port adapted to receive the second container, a third port adapted to receive a syringe, a first fluid pathway that enables fluid flow between the first port and the third port, a second fluid pathway that enables fluid flow between the third port and the second port, a third fluid pathway that enables fluid flow between the second port and the third port, a first flow control member disposed between the first port and the third port, enabling one-way fluid flow from the first port to the third port when a syringe is coupled to the third port, a second flow control member disposed between the third port and the second port, enabling one-way fluid flow from the third port to the second port when a syringe is coupled to the third port, and a third flow control member. The third flow control member provides for user selective switching between a first state in which fluid flow is enabled between the first port and the third port via the first fluid pathway and between the third port and the second port via the second fluid pathway, and a second state in which fluid flow is enabled between the second port and the third port via the third fluid pathway but disabled between the first port and the third port. 
         [0020]    By the above mixing system, the syringe is allowed to receive the first contents from the first container and to transfer the first contents to the second container, respectively receive a volume of material which has been formed by mixing the first contents and the second contents. 
         [0021]    The above arrangement enables a user to perform the transfer of the first contents from the first container to the second container and the transfer of the mixed product from the second container to the syringe in a safe way while maintaining sterility during the whole procedure. Further, the steps of withdrawing the plunger in the syringe, which causes the first contents to move from the first container to the syringe, and subsequently advancing the plunger in the syringe, which causes the first contents to move from the syringe to the second container, are intuitively comprehensible and easy to carry out by the user as they resemble the traditional steps for transferring a medium from one container to another using a syringe with a needle. 
         [0022]    The first contents may be a liquid material, such as a diluent which is suitable as a solvent for a powdered or lyophilized drug, and the second contents may be a dry material, such as a powdered or lyophilized drug. In this case the material formed when the first contents and the second contents are mixed is a reconstituted drug being ready for delivery to a user, e.g. by means of infusion or injection. Alternatively, the first contents as well as the second contents may be liquid materials. 
         [0023]    The first container may be any suitable kind of container, such as a vial, a flexible container, etc. Similarly, the second container may be any suitable kind of container. 
         [0024]    Generally, when a powdered drug has been reconstituted, great care must be taken to assure that the drug solution does not foam during the transfer to the syringe as this may introduce a risk of the user subsequently injecting or infusing volumes of air into the bloodstream or tissue along with the drug solution. 
         [0025]    Thus, in an embodiment of the invention, the transfer unit of the mixing system further comprises a fourth flow control member in the third fluid pathway for substantially eliminating foaming when the drug solution formed by the mixing of the first and second contents is transferred to the syringe. In a specific preferred embodiment, the fourth flow control member acts to reduce/restrict the flow rate of the drug solution when the third flow control member is positioned so that fluid flow from the second port to the third port via the third fluid pathway is enabled. The fourth flow control member would constitute a cross-sectional area reduction of the third fluid pathway. 
         [0026]    According to one embodiment, fluid flow from the first port to the third port is enabled when the fluid pressure in the third port exceeds a predefined negative pressure, caused by withdrawing a plunger of the syringe. According to this embodiment, the first contents may be moved from the first container to the syringe via the first fluid pathway due to a decrease in pressure at the third port. The aspiration of the first contents from the first container may cause a negative pressure build-up in the first container. This negative pressure can be compensated by allowing ambient air to enter into the first container. One way to allow ambient air to enter into the first container is to provide a vent in the transfer unit that enables air flow between the outside and the first port. 
         [0027]    Alternatively, a pre-established positive pressure in the first container could provide the fluid flow from the first port to the third port automatically when the syringe is connected to the third port. 
         [0028]    In one embodiment, the first port comprises two channels. One of these channels may be a liquid channel dedicated to the transfer of the first contents out of the first container while the other channel may be an air channel being fluidly connected to a vent to allow for air flow between the first container and the outside. The vent may be provided with a fifth flow control member enabling one-way fluid flow from the outside to the first container. 
         [0029]    In such a construction air bubbles may enter the liquid channel when the first contents is moved from the first container to the syringe. However, if the air channel opening is arranged above the liquid channel opening during aspiration of the first contents from the first container, essentially no air will be transferred along with the first contents. 
         [0030]    In one embodiment, the first container is provided with a closure, e.g. in the form of a penetrable membrane, in order to ensure sterility of the first contents. The first port is adapted to penetrate this membrane to establish fluid connection between the first container and the first fluid pathway. In case the penetration is performed by two individual piercing members, e.g. two needles, the connecting interface may be unstable, e.g. due to the relatively small dimensions, which may result in breakage of one or both of the individual piercing members. Furthermore, the introduction of two individual piercing members through the membrane increases the risk of leakage of the first contents from the first container. 
         [0031]    Thus, in an embodiment of the invention the first port comprises an asymmetric hollow spike or needle having two internal channels, the openings of which are axially offset to allow for transfer of the first contents from the first container to the third port with essentially no inclusion of air. 
         [0032]    The transfer unit may comprise a filter arranged in the vent to further minimise the risk of contamination of the first contents in case any air bubbles should, unexpectedly, enter the liquid channel. 
         [0033]    Alternatively or additionally, the transfer system may comprise a filter arranged in the third fluid pathway. Such a filter can be used for preventing impurities from being transferred from the second container to the syringe when the drug solution is transferred to the syringe. Such impurities could, e.g., be rubber particles originating from a stopper of a vial and being created during penetration of the stopper, and/or dry contents which has not been properly solved. 
         [0034]    The syringe may in the above described arrangements be connected to the transfer unit in a state where the plunger is fully advanced. This will provide for a perfectly sterile mixing system as no contaminated air is allowed to enter the system during a mixing procedure. 
         [0035]    When the spike penetrates the closure of the first container a positive pressure may be generated in the first container, potentially leading to a small volume of the first contents being forced out through the spike. If the vent is not provided with a flow control member preventing fluid flow from the first container to the outside this volume of the first contents may be forced completely out of the transfer unit whereby it will be lost to the surroundings. This is definitely undesirable as it will lead to an imbalance in the volumetric relationship between the first contents and the second contents, resulting in the final mixed product getting a higher potency than intended. Furthermore, the user will experience a leaking device, which may cause him to question the reliability of the product. 
         [0036]    In another aspect of the invention a medical mixing system is provided comprising a first container containing first contents, a second container containing second contents, and a transfer unit. The transfer unit comprises a housing, a first port adapted to receive the first container, a second port adapted to receive the second container, a third port adapted to receive a variable volume reservoir, e.g. a syringe, a plurality of fluid pathways for interconnecting the first port, the second port, and the third port, e.g. as described above in relation to the first aspect, and a reservoir in fluid communication with the first port. 
         [0037]    In a particular embodiment the first port comprises a dual channel spike, and the reservoir is in fluid communication with one of the channels in the spike. 
         [0038]    The reservoir may further be in fluid communication with ambient air, e.g. via an opening in the transfer unit housing, and it may comprise a serpentine channel segment of which the end portion is in direct fluid communication with the ambient air. Thereby a tortuous path is provided reducing the risk of the escaped volume of the first contents leaking out of the reservoir during user preparation of the mixing system. 
         [0039]    By including a reservoir in the transfer unit leakage of the first contents is effectively prevented because any escaped material will accumulate in the reservoir, and once the user commences the mixing procedure by sucking the first contents out of the first container the small volume of first contents which may have escaped through the spike at penetration of the container closure will simply be drawn from the reservoir back into the first container and further into the first fluid pathway along with the bulk of the first contents. Thereby it is ensured that the entire volume of the first contents is aspired into the syringe and used for mixing with the second contents, i.e. that the final administrable drug has the prescribed potency. 
         [0040]    When the first contents have been transferred to the second container to mix with the second contents the user may operate the third flow control member to allow transfer of the mixed product from the second container to the syringe. This may be done by forcing the third flow control member to move from a first position to a second position in the transfer unit, e.g. by rotating the third flow control member in the transfer unit housing. The third flow control member may be in the form of a plug comprising an axisymmetric, e.g. a circular cylindrical or conical, plug body adapted to fit tightly in the transfer unit housing and an enlarged grip portion enabling the user to rotate the third flow control member from outside the transfer unit housing. 
         [0041]    The plug body may be provided with channel segments arranged in such a manner that when the third flow control member is in the first position a first channel segment constitutes a portion of the first fluid pathway and a second channel segment constitutes a portion of the second fluid pathway, and when the third flow control member is in the second position a third channel segment constitutes a portion of the third fluid pathway. Importantly, when the third flow control member is in the second position there is no fluid connection between the first port and the third port, whereby it is ensured that no air is introduced via the first fluid pathway in the transfer of the mixed product from the second container to the syringe. The mixed product is therefore not in risk of being contaminated by ambient air, just as the risk of foaming is minimised. 
         [0042]    In a particular embodiment the first channel segment and the second channel segment share a channel segment portion. 
         [0043]    The channel segments may be arranged on the surface of the plug body, e.g. as grooves in the plug material, and may be circumferentially separated in such a manner that when the third flow control member is in the first position the first channel segment completes the first fluid pathway and the second channel segment completes the second fluid pathway while the third fluid pathway is disconnected, and when the third flow control member is in the second position the third channel segment completes the third fluid pathway while the first fluid pathway and the second fluid pathway are disconnected, respectively. 
         [0044]    The particular arrangement of the channel segments on the surface of the plug body determines the angular movement of the third flow control member required to switch between the first state and the second state. In a specific embodiment the channel segments are arranged such that a substantially 90 degrees rotation of the third flow control member is required to switch between the first state and the second state. 
         [0045]    If the channel segments are arranged on the surface of the plug body it is important to provide a fluid tight fit between the plug and the transfer unit housing. Otherwise, a part of the liquid being transferred may in fact leak out of the housing along the plug body. On the other hand, since the third flow control member is user operable the fit should not be so tight as to cause a high friction interface that makes the third flow control member difficult to rotate. 
         [0046]    In a further aspect of the invention a flow control member for a fluid transfer unit, e.g. as described in the above, is provided comprising an axi-symmetric body of a first material, a grip portion for user operation, and two or more channel segments arranged on the surface of the axi-symmetric body, wherein the channel segments are defined by at least one ridge. 
         [0047]    The at least one ridge may be of a second material different from the first material in which case the flow control member may be manufactured using a two-component moulding process. The first material may e.g. be a thermoplastic polymer, such as HDPE, and the second material may e.g. be a thermoplastic elastomer, such as TPV, or a thermoset elastomer. 
         [0048]    By providing such a dual component body the sealing capability of the flow control member is improved considerably, while a low friction is established between the contacting surfaces of the transfer unit and the flow control member. This allows the user to rotate the flow control member applying only a slight torque. 
         [0049]    The third port may comprise a connector for coupling with the syringe. The syringe may e.g. be of the Luer lock type comprising an internally threaded retaining collar, and the connector may e.g. comprise an external screw thread onto which the syringe can be attached. Alternatively, other types of connections between the syringe and the third port may be employed, such as e.g. a press-fit or a bayonet coupling. In relation to the attachment of the syringe to the third port it is important that the syringe cannot be forced, e.g. screwed, too far onto the connector since this may cause the tapered outlet portion of the syringe to break rendering both the syringe and the transfer unit useless. 
         [0050]    In a further aspect of the invention a transfer unit for a medical mixing system is provided comprising a housing, a first port adapted to receive a first container, a second port adapted to receive a second container, a third port adapted to receive a variable volume reservoir, e.g. a syringe, a plurality of fluid pathways for interconnecting the first port, the second port, and the third port, e.g. as described above, and a contact face adapted to abut with the variable volume reservoir when the variable volume reservoir is coupled with the third port. 
         [0051]    The contact face may be arranged at the third port and may be adapted to abut with a contact face of the syringe, e.g. a retaining collar of a Luer lock syringe, so as to provide a distinct stop for further translatory movement of the syringe relative to the transfer unit in the direction of attachment. 
         [0052]    Such a distinct stop will provide a safety against the syringe being mishandled during attachment to the transfer unit, e.g. against the syringe being screwed too far onto a connector of the third port, because the user will be able to differentiate between proper and improper attachment. The user will simply sense the abutment between the contact face of the transfer unit and that of the syringe and will intuitively know that no further movement is needed. 
         [0053]    According to one embodiment, fluid flow from the third port to the second port is enabled when the syringe plunger is advanced to expel the first contents out of the syringe and into the second fluid pathway. This will move the first contents to the second container and create an excess pressure in the second container due to the compression of the air molecules present therein. The system will remain in this pressurised condition until the third flow control member is manipulated to enable fluid flow from the second port to the third port via the third fluid pathway. Such a manipulation will result in the drug solution being forced out of the second container and into the third fluid pathway by the expanding air. 
         [0054]    If a syringe is not coupled to the third port at the time where the third flow control member is manipulated to enable fluid flow from the second port to the third port via the third fluid pathway, some or all of the drug solution may just flow out of the system through the third port and be wasted to the surroundings. 
         [0055]    Thus, in a further aspect of the invention a transfer unit for a medical mixing system is provided comprising a first port adapted to receive a first container containing first contents, a second port adapted to receive a second container containing second contents, a third port adapted to receive a variable volume reservoir, a plurality of fluid pathways for interconnecting the first port, the second port, and the third port, e.g. as described above in relation to the first aspect, and a user operable flow control member enabling user selective fluid flow from the second port to the third port, wherein the transfer unit further comprises a locking means adapted to engage with the user operable flow control member to prevent movement of the user operable flow control member, and wherein the locking means is configured to disengage with the user operable flow control member in response to a variable volume reservoir being coupled to the third port. The transfer unit may further comprise any features and elements mentioned in connection with the above aspects. 
         [0056]    The locking means is provided to ensure that the user operable flow control member can only be manipulated to enable fluid flow from the second port to the third port when a variable volume reservoir, such as a syringe, is coupled to the third port. 
         [0057]    According to one embodiment the locking means comprises a mechanical engagement between a catch member and the user operable flow control member, e.g. between a protrusion and a recess. The catch member may be biased so that the user operable flow control member is maintained in its position by the mechanical interaction between the catch member and the user operable flow control member as long as a syringe is not coupled to the third port. When a syringe is coupled to the third port a mechanical interface between the syringe and the locking means will provide for a release mechanism that moves the catch member out of engagement with the user operable flow control member, thus allowing for manipulation of the user operable flow control member. 
         [0058]    The bias on the catch member may be provided by a structure of which the catch member itself is a part. Alternatively, or additionally, the bias may be provided by one or more separate resilient elements. 
         [0059]    The locking means may further be configured to re-engage with the user operable flow control member in response to the variable volume reservoir being decoupled from the third port. 
         [0060]    The mechanical engagement between the catch member and the user operable flow control member may be realised by an interaction between a protrusion and a recess. The recess may be provided in the user operable flow control member or, alternatively, in the locking means. Hence, the catch member may comprise a protrusion or a recess. 
         [0061]    In a particular embodiment the locking means has an elastically deformable geometry and is arranged in the transfer unit in such a manner that it biases the catch member towards the user operable flow control member. This ensures that the catch member reengages with the user operable flow control member to lock the user operable flow control member in position when the syringe is removed from the third port. 
         [0062]    The catch member may be an integral part of the locking means or it may be a separate element suitable for physical connection with the locking means. 
         [0063]    The provision of a locking means as described above in connection with a fluid tight system, also as described above, enables the user to prepare one or more containers containing a drug solution or mixed material for subsequent transfer to a syringe without having to worry about the concentration or the sterility of the drug solution. Pooling of the contents of several containers is thereby safe and easy. 
         [0064]    In a further aspect, the invention relates to a container unit for a medical mixing system according to the first aspects, the container unit comprising a first container containing first contents and a second container containing second contents to be mixed with said first contents. 
         [0065]    In an embodiment of the invention the containers are pre-arranged in the container unit by the manufacturer, and it can thereby be ensured that the first contents and the second contents match, e.g. in terms of amount and kind. Accordingly, when the first contents and the second contents are mixed, the risk of errors occurring during mixing of the contents is thereby minimised. The containers are preferably irremovably arranged in a mutually fixed position in the container unit. 
         [0066]    The first and second container may alternatively be provided as separate containers, i.e. not fixed in the same housing. 
         [0067]    The container unit and the transfer unit are adapted to be coupled together to form a mixing system or a mixing kit. The units may advantageously be delivered together in one package. In order to mix the first contents and the second contents, the user must couple the units together, and possibly operate one or more features of the transfer unit, e.g. one or more flow control members and/or a plunger of a syringe, in order to cause the first contents to move to the second container or the drug solution to move to the syringe. Thereby the container unit may be maintained under sealed conditions during storage. This increases the expected lifetime of the contents of the containers, and counteracts contamination of the contents. Finally it is a large advantage for the manufacturer to produce the container unit separately as the number of parts requiring absolute sterile production facilities is minimised, i.e. minimal production complexity. Thus, the invention provides a mixing system that is simple and cost efficient to produce. 
         [0068]    Furthermore, by providing the container unit and the transfer unit as a kit it can be ensured that the transfer unit is actually suitable for mixing the contents of the first and second containers. 
         [0069]    The container unit and the transfer unit may be shaped in such a manner that they can only be coupled together when being positioned at a predetermined mutual orientation. According to this embodiment, it can be ensured that the first container is coupled to the first port and the second container is coupled to the second port when the container unit and the transfer unit are coupled together. Thereby it is also ensured that the first container, the second container and the syringe are interconnected in a correct manner by the flow channels, and that the fluid flows in the transfer unit during mixing of the first and second contents are as expected. Accordingly, a correct mixing of the first contents and the second contents can be ensured. A way of ensuring a predetermined mutual orientation is to shape the container unit and the transfer unit in an asymmetric manner, e.g. so that each has a straight edge and a curved edge opposing the straight edge. 
         [0070]    In a further aspect of the invention a method for mixing substances is provided, comprising a) coupling a container unit, comprising a first container and a second container, and a fluid transfer unit comprising first coupling means for establishing fluid connection to the first container, second coupling means for establishing fluid connection to the second container, third coupling means for establishing fluid connection to a variable volume reservoir, a plurality of fluid pathways interconnecting the first coupling means, the second coupling means and the third coupling means, and a flow control member, b) attaching a variable volume reservoir to the third coupling means, c) increasing the volume of the variable volume reservoir, and d) decreasing the volume of the variable volume reservoir. 
         [0071]    The fluid transfer unit may further comprise a user operable flow control member, and the method may further comprise e) turning the user operable flow control member from a first position to a second position, and f) increasing the volume of the variable volume reservoir. 
         [0072]    The latter steps of the method will ready the mixed product for direct administration from the variable volume reservoir, e.g. via an infusion set, once the variable volume reservoir has been detached from the third coupling means. 
         [0073]    The variable volume reservoir may comprise a syringe, e.g. a Luer lock syringe, or indeed any kind of container capable of increasing and decreasing its internal volume, such as a flexible bag. 
         [0074]    In the present specification reference to a certain aspect or a certain embodiment (e.g. “an aspect”, “a first aspect”, “one embodiment”, “an exemplary embodiment”, or the like) signifies that a particular feature, structure, or characteristic described in connection with the respective aspect or embodiment is included in at least that one aspect or embodiment of the invention, but not necessarily in all aspects or embodiments of the invention. It is emphasized, however, that any combination of features, structures and/or characteristics described in relation to the various aspects and embodiments of the invention is encompassed by the invention unless otherwise indicated herein or clearly contradicted by context. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0075]    In the following the invention will be further described with references to the drawings, wherein 
           [0076]      FIG. 1  shows a schematic view of a mixing system according to an embodiment of the invention, 
           [0077]      FIG. 2  shows a schematic view of a mixing system according to another embodiment of the invention, 
           [0078]      FIG. 3  shows a cross-sectional view of a hollow spike according to an embodiment of the invention, 
           [0079]      FIG. 4  shows a perspective view of a transfer unit of a mixing system according to an embodiment of the invention, 
           [0080]      FIGS. 5   a  and  5   b  show perspective views of a user operable flow control member according to an embodiment of the invention, 
           [0081]      FIG. 6   a  shows a cross-sectional view of the basic set-up of a locking means according to an embodiment of the invention, 
           [0082]      FIGS. 6   b - 6   d  show cross-sectional views of the operating principle of a locking means according to an embodiment of the invention, 
           [0083]      FIG. 7  shows a perspective view of a mixing system according to an embodiment of the invention in a disassembled state, 
           [0084]      FIG. 8  shows a perspective view of the mixing system of  FIG. 7  in an assembled state, 
           [0085]      FIG. 9  shows a perspective view of a transfer unit according to another embodiment of the invention, 
           [0086]      FIG. 10  shows a perspective view of a cover plate for the transfer unit of  FIG. 9 , 
           [0087]      FIGS. 11   a  and  11   b  show perspective views of a user operable flow control member according to another embodiment of the invention, and 
           [0088]      FIG. 12  shows a cross-sectional view of a stop defining arrangement according to an embodiment of the invention. 
       
    
    
       [0089]    In the figures like structures are mainly identified by like reference numerals. 
       DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0090]    When in the following relative expressions, such as “inwards” and “outwards”, are used, these refer to the appended figures and not necessarily to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only. 
         [0091]    The following text provides a description of exemplary embodiments of the invention. 
         [0092]    The present invention is directed to systems for reconstituting a dry drug by mixing the dry drug with a solvent or liquid. The reconstitution system includes a transfer unit which is able to connect to a couple of containers, respectively a variable volume reservoir, such as a syringe, and which enables subsequent transfer of the contents of the one container to the other. The transfer unit further enables transfer of the final drug solution to the syringe. 
         [0093]      FIG. 1  shows a schematic representation of a mixing system  1  in which a first container  2 , containing a predetermined amount of a diluent  8 , a second container  3 , containing a predetermined amount of powdered drug  9 , and a syringe  20  are connected to a transfer unit  5 . 
         [0094]    In the depicted embodiment, the two containers  2  and  3  are formed as standard vials each having a piercable septum closing the vial and having a retaining cap for fixedly retaining the septum. 
         [0095]    Transfer unit  5  comprises a housing  10  (see  FIGS. 4 and 7 ) which houses the necessary fluid pathways, control members and ports. The housing  10  may be designed to receive the two containers  2  and  3 , so that they are partly or fully accommodated inside the housing  10 . Alternatively, the housing  10  may be designed to only encircle the cap parts of the vials. 
         [0096]    Transfer unit  5  is provided with a first port  11  adapted to receive the first container  2  and a second port  12  adapted to receive the second container  3 . The ports  11  and  12  may be adapted to receive each of the two containers  2  and  3  in a first condition and a second condition. In the first condition, the two containers  2  and  3  are only retained in the housing and no fluid communication to the interior of the two containers  2  and  3  is established. In this first condition, the transfer system  5 , including the two containers  2  and  3 , can be stored long term. In the second condition fluid communication is established between the fluid pathways of transfer unit  5  and containers  2  and  3 . 
         [0097]    The coupling ports  11  and  12  may in principle comprise any means of providing fluid communication with the inside of the containers  2  and  3 , such as hollow needles, hollow spikes etc. Preferably, if needles or spikes penetrating the septum are used, the needles or spikes are formed so that substantially no residual liquid can be trapped inside the containers  2  and  3 . 
         [0098]    Housing  10  further comprises coupling means in the form of a third port  13  for releasable coupling of a syringe  20  having a sealing plunger  21  slideably mounted inside. Preferably, the open (distal) end of syringe  20  comprises means for releasably attaching a conduit by a releasable connector, such as a Luer connector of an infusion set. 
         [0099]    Accordingly, housing  10  comprises corresponding connection means for releasably connecting the syringe  20  to the third port  13 . 
         [0100]      FIG. 1  further shows a first fluid pathway  14  that enables fluid flow between the first port  11  and the third port  13 . Further, the third port  13  and the second port  12  are fluidly connected via a second fluid pathway  15 . Also, second port  12  and third port  13  are in fluid communication via a third fluid pathway  16 . 
         [0101]    At one point along the first fluid pathway  14 , a first flow control member  17 , preferably in the form of a check valve or non-return valve, is provided resulting in a one-way fluid flow from the first port  11  to the third port  13 . 
         [0102]    At one point along the second fluid pathway  15 , a second flow control member  18 , preferably in the form of a check valve or non-return valve, is provided resulting in a one-way fluid flow from the third port  13  to the second port  12  via the second fluid pathway  15 . 
         [0103]    A third flow control member  19 , e.g. in the form of a dial plug, is further provided enabling a user to selectively switch between a first state in which fluid flow is enabled between the first port  11  and the third port  13  via the first fluid pathway  14  and between the third port  13  and the second port  12  via the second fluid pathway  15 , and a second state in which fluid flow is enabled between the second port  12  and the third port  13  via the third fluid pathway  16 . 
         [0104]    At one point along the third fluid pathway  16 , a fourth flow control member  22 , e.g. in the form of a throttle valve, is provided as a restriction to reduce the flow rate of fluid moving from the second port  12  to the syringe  20 . The function of the fourth flow control member  22  will be described in more detail below in the section regarding the operation of the mixing system. 
         [0105]    To allow for entry of ambient air into the first container  2  in connection with the transfer of the diluent  8  out of the first container  2  a vent  25  is provided in the transfer unit  5  fluidly connecting the first port  11  with the outside. The first port  11  thus comprises both a fluid pathway dedicated to transfer the diluent  8  out of the first container  2  and a fluid pathway dedicated to allow entry of air into the first container  2 . 
         [0106]    At one point along the vent  25 , a fifth flow control member  23 , preferably in the form of a check valve or non-return valve, is provided resulting in a one-way fluid flow from the outside to the first port  11 . The vent  25  is further provided with a filter  24  so that no contaminated air is allowed to enter the first container  2 . 
         [0107]      FIG. 2  shows a schematic representation of a mixing system  100  according to an alternative embodiment. In this embodiment a first container  102 , containing a predetermined amount of a diluent, a second container  103 , containing a predetermined amount of powdered drug, and a syringe  120  are connected to a transfer unit  105  in the same manner as described above. A first fluid pathway  114  enables fluid flow between a first port  111  and a third port  113  and a second fluid pathway  115  enables fluid flow between the third port  113  and a second port  112 . 
         [0108]    A non-return valve  117  is provided in the first fluid pathway  114  resulting in a one-way fluid flow from the first port  111  to the third port  113 . Further, a non-return valve  123  is provided in a vent  125  resulting in a one-way fluid flow from the outside to the first container  102 . 
         [0109]    A third flow control member  119 , e.g. in the form of a dial plug, is provided enabling a user to selectively switch between a first state in which fluid flow is enabled between the first port  111  and the third port  113  via the first fluid pathway  114  and a second state in which fluid flow is enabled between the second port  112  and the third port  113  via the second fluid pathway  115 . 
         [0110]      FIG. 3  shows a first hollow spike  30  serving to establish fluid connection between the first container  2  and the first fluid pathway  14 . The first hollow spike  30  comprises two internal channels, a liquid channel  31  dedicated to transfer the diluent  8  out of the first container  2 , and an air channel, dedicated to allow vented air to enter the first container  2 . The opening of the air channel  32  is axially offset from the opening of the liquid channel  31  to reduce the likelihood of air bubbles entering the liquid channel  31  during transfer of the diluent  8  out of the first container  2 . A second hollow spike  57  (see  FIG. 7 ) is used in a like way to establish fluid connection between the second container  2  and the second fluid pathway  15  (also between the second container  2  and the third fluid pathway  16 ). The second hollow spike  57  is preferably a single channel spike, but it could alternatively be a double channel spike (e.g. one channel for each of the pathways  15 ,  16  of  FIG. 1 ). 
         [0111]      FIG. 4  shows a perspective view of the transfer unit  5  of  FIG. 1 , including its various fluid pathways. The first and second hollow spikes  30 ,  57  are not visible in this view as they protrude from the backside of the transfer unit  5 . However, the liquid channel  31  is fluidly connected with a diluent evacuation node  71 , and the air channel  32  is fluidly connected with an air inlet node  72 . Likewise, the single channel in the second hollow spike  57  is fluidly connected with a mixing node  73 . Thereby, fluid flow is enabled between the first port  11  and a first flow channel  34 , respectively between the first port  11  and the vent  25 , and between the second port  12  and respective second and third flow channels  35 ,  36 . The third flow channel  36  is further fluidly connected with a delivery node  74  through which the administrable drug flows when evacuated from the second container  3  after mixing of the diluent  8  and the powdered drug  9 . The flow channels  34 ,  35 ,  36  are provided as in-moulded channels in the top face  7  of the housing  10 , as shown. 
         [0112]      FIGS. 5   a  and  5   b  show perspective views of the third flow control member or dial plug  19 . Dial plug  19  comprises an elongated plug body  40  and a dial  41  intended for manipulation of the dial plug  19  by a user of the mixing system  1 .  FIG. 5   a  shows a first channel segment  42  in the plug body  40  which channel segment  42  constitutes a part of the first fluid pathway  14  fluidly connecting the first port  11  and the third port  13  as well as of the second fluid pathway  15  fluidly connecting the third port  13  and the second port  12 , when the dial plug  19  is in a first position. The first channel segment  42  is “T”-shaped and consists of a main portion  44 , a first branch  45  and a second branch  46 .  FIG. 5   b  shows an “L”-shaped second channel segment  43  in the plug body  40  which channel segment  43  constitutes a part of the third fluid pathway  16  fluidly connecting the second port  12  and the third port  13 , when the dial plug  19  is in a second position. Both the first channel segment  42  and the second channel segment  43  are provided as grooves in the dial plug  19 . 
         [0113]      FIG. 6   a  shows a close-up cross sectional view of the third port  13  highlighting the basic principle of a lock  50  for the third flow control member  19 .  FIG. 6   a  shows the syringe  20  (only the distal most portion is shown) just before coupling to a connecting piece  56  at the third port  13 . In this position, the syringe  20  touches an abutting surface  54  of the lock  50  in a lock/syringe interface  53 . The third flow control member  19  is prevented from rotational movement by a catch member  51  which is biased by a spring means  52  to protrude into a groove  55  in the plug body  40  of the third flow control member  19 . 
         [0114]      FIG. 6   b  shows a cross sectional view A-A (see  FIG. 4 ) corresponding to the view of  FIG. 6   a . The lock  50  has a flexible structure and comprises a couple of “S”-shaped arms  58  extending laterally from a central piece  65 . The arms  58  terminate in peripheral parts of the housing  10  and are supported (not shown) at their respective ends  59  in such a manner that the ends  59  are prevented from moving relative to the housing  10 . A collar  63  of the syringe  20  only just abuts the central piece  65 . 
         [0115]      FIGS. 6   c  and  6   d  show different stages of engagement between an inner thread  62  in the collar  63  and an outer thread  61  on the connecting piece  56 . As the lock/syringe interface  53  is moved gradually inwards away from the opening of the third port  13  as a consequence of the syringe  20  being screwed onto the connecting piece  56 , the biasing force of the arms  58  is overcome and the arms  58  are deflected, whereby the catch member  51  is carried completely out of engagement with the groove  55  ( FIG. 6   d ). When the syringe  20  is tightly fastened to the third port  13 , the third flow control member  19  is free to be rotated and thereby to switch between the first state in which fluid flow is enabled between the first port  11  and the third port  13  via the first fluid pathway  14  and between the third port  13  and the second port  12  via the second fluid pathway  15 , and the second state in which fluid flow is enabled between the second port  12  and the third port  13  via the third fluid pathway  16 . 
         [0116]    Similarly, with reference to  FIG. 2 , when the syringe  20  is tightly fastened to the third port  13 , the third flow control member  19  is free to be rotated and thereby to switch between enabling fluid flow between the first port  11  and the third port  13  and between the second port  12  and the third port  13 . 
         [0117]    Because of the resilient structure of the lock  50  and the retained ends  59  if the syringe  20  is detached from the third port  13  while the third flow control member  19  is in a position corresponding to the first state the arms  58  will return to their initial positions and thereby force the catch member  51  back into engagement with the groove  55 . This ensures that the third flow control member  19  can not be rotated to switch from the first state to the second state unless a syringe is coupled to the third port  13 . 
         [0118]    A Luer lock connection between the syringe  20  and the connecting piece  56  at the third port  13  is just one example of a fitting between the syringe  20  and the third port  13 . Other non-limiting examples include, e.g., a snap fit coupling or a bayonet coupling. 
         [0119]      FIG. 7  is a perspective view of a disassembled mixing system  1  according to an embodiment of the invention. The mixing system  1  comprises a container unit  26  and a transfer unit  5  as described in detail above, the container unit  26  and the transfer unit  5  being adapted to be coupled together to form the drug mixing system  1 . 
         [0120]    The container unit  26  comprises a housing  39 , a first container  2  containing first contents in the form of a diluent, and a second container  3  containing second contents in the form of a dry drug. The containers  2 ,  3  are fixed in the housing  39 , and it is thereby ensured that the first contents and the second contents match, e.g. in terms of amount and kind. Each of the containers  2 ,  3  is provided with a removable cap  27 . 
         [0121]    The container unit  26  is provided with a wall part  28  which is arranged asymmetrically on the housing  39 . The transfer unit  5  is provided with a corresponding groove  29  adapted to accommodate the wall part  28 . Thereby it is ensured that it is only possible to couple the container unit  26  and the transfer unit  5  in such a manner that the first port  11  is coupled to the first container  2  and the second port  12  to the second container  3 , and not vice versa. Accordingly, it is ensured that the fluid flows in the assembled mixing system  1  are correct. 
         [0122]    The transfer unit  5  comprises a first port  11  adapted to receive the first container  2 , a second port  12  adapted to receive the second container  3 , and a third port  13  adapted to receive a syringe (not shown). The transfer unit  5  is further provided with a number of flow channels (not visible) connecting the ports  11 ,  12 ,  13  in such a manner that, when the transfer unit  5  and the container unit  26  are coupled together, the diluent is allowed to move from the first container  2  to a syringe coupled to the third port  13 , from the syringe on to the second container  3  in order to allow the diluent and the dry drug to mix, and in such a manner that the mixed material is subsequently allowed to move to the syringe. The spikes  30 ,  57  of the ports  11 ,  12  are also shown. 
         [0123]      FIG. 8  is a perspective view of the mixing system  1  of  FIG. 7  in an assembled state. 
       Operation of the Mixing System 
       [0124]    The mixing system of  FIG. 1  comprising the various structures and features of the components shown in  FIGS. 3-8  may be operated in the following manner. When it is desired to mix the diluent  8  and the powdered drug  9 , the caps  27  are removed and the transfer unit  5  is connected to the container unit  26  in such a manner that the first container  2  is received in the first port  11  and the second container  3  is received in the second port  12 . 
         [0125]    In practice, the first hollow spike  30  will thereby penetrate the membrane  6  of the first container  2  to establish fluid connection between the first container  2  and the first fluid pathway  14 . Similarly, the second hollow spike  57  will penetrate the membrane (not shown) of the second container  3  to establish fluid connection between the second container  3  and the second fluid pathway  15 . 
         [0126]    The syringe  20  with a fully, or substantially fully, advanced plunger  21  is then coupled to the third port  13 . The transfer unit is provided by the manufacturer in a ready-to-use condition, i.e. where the dial plug  19  is in a position corresponding to the first state in which fluid flow is enabled between the first port  11  and the third port  13  via the first fluid pathway  14  and between the third port  13  and the second port  12  via the second fluid pathway  15 . 
         [0127]    The mixing system  1  is held vertically so that the two containers  2  and  3  are positioned above the syringe  20 , and the plunger  21  is pulled back. This will cause the check valve  17  to open while the check valve  18  remains closed. Accordingly, the diluent  8  is sucked out of the first container  2  and transferred to the syringe  20  via the liquid channel  31 , the diluent evacuation node  71 , the first flow channel  34 , the first branch  45 , and the main portion  44 . The check valve  18  ensures that air or material is not sucked from the second container  3  into the syringe  20  during this operation. Further, ambient air is sucked into the first container  2  via the vent  25 , the air inlet node  72 , and the air channel  32 . When the mixing system is held in this position, the opening of the air channel  32  in the first hollow spike  30  is arranged above the opening of the liquid channel  31 . This ensures that no, or a minimum of, air bubbles are transferred along with the diluent  8  from the first container  2  to the syringe  20 . 
         [0128]    When a sufficient amount of the diluent  8 , e.g. all of the diluent  8 , has been transferred to the syringe, the plunger  21  is pushed forward. This will close the check valve  17  and open the check valve  18  to allow transfer of the diluent  8  from the syringe  20  to the second container  3  via the main portion  44 , the second branch  46 , the second flow channel  35 , the mixing node  73 , and the second hollow spike  57 . The transfer of the diluent  8  into the second container  3  causes an increase in pressure in the second container  3 . The check valve  18  and the dial plug  19 , being in a position corresponding to the first state, prevent any of the diluent  8  and the powdered drug  9  from leaving the second container  3 . 
         [0129]    When the diluent  8  and the powdered drug  9  have mixed properly to form a drug solution, the dial  41  is turned, e.g. approximately 90 degrees. This will result in the dial plug  19  switching from the first state to the second state in which fluid flow is enabled between the second port  12  and the third port  13  via the third fluid pathway  16 . The increased pressure in the second container  3  will drive some or all of the drug solution out of the second container  3  and into the syringe  20  via the second hollow spike  57 , the mixing node  73 , the third flow channel  36 , the delivery node  74 , and the second channel segment  43 . If not all of the drug solution is forced out of the second container  3  and into the syringe  20  by means of the increased pressure in the second container  3 , the plunger  21  may be manually retracted in addition to ensure that the second container  3  is being emptied. Importantly, when the dial plug  19  is in the second state fluid flow is disabled between the first port  11  and the third port  13 . This ensures that no unwanted residual contents of the first container  2  or potentially contaminating ambient air can accidentally be sucked into the syringe  20  to mix with the drug solution when the user prepares for delivery by transferring the administrable drug from the second container  3  to the syringe  20 . 
         [0130]    The above described transfer of drug solution from the second container  3  to the syringe  20  due to the increased pressure in the second container  3  may be executed so fast that the drug solution begins to foam. The throttle valve  22  in the third fluid pathway  16  eliminates this risk by reducing the flow rate of the drug solution to a level where foaming will not take place. Avoiding foaming is highly important for several kinds of drugs, in particular drugs that must be administered intravenously. 
         [0131]    The fact that the system can be left in the first state for a period of time is of high importance to the user if he needs to mix further doses from similar mixing systems (so-called “pooling” as mentioned earlier) before infusing the drug. In case, a person needs to reconstitute more drug than what is provided in a single powdered drug container, a number of mixing systems can be prepared to the step where the diluent has been transferred to the second container and mixed with the powdered drug. The individual containers containing the final drug solutions can then be emptied successively by successively coupling a syringe to each of the third ports and turning the respective dials to allow the mixed contents to be forced out of the pressurised containers. All the prepared doses can then e.g. be accumulated in the same syringe and infused or injected in one go, which is highly preferable for the users, in particular patients requiring intravenous infusion. 
         [0132]    As can be understood from the above operational steps, the invention provides a mixing system which is extremely simple and efficient for users to operate. 
         [0133]      FIG. 9  shows, in an alternative embodiment, a transfer unit  205  for use in the mixing system  1 . The basic functionality of the transfer unit  205  is similar to the functionality of the previously described transfer unit  5 . However, this embodiment of the transfer unit  205  offers an additional feature which will be apparent from the following description. 
         [0134]    The transfer unit  205  has a housing  210  with a top face  207  comprising a number of inmoulded channels. A first hollow spike (not visible) protruding from the backside of the transfer unit  205  is adapted to establish fluid connection with a diluent container (not shown) when the diluent container is received in a first port (not visible). This spike has a liquid channel (not visible) and an air channel (not visible) similar to the first hollow spike  30  described above. The liquid channel is fluidly connected with a diluent evacuation node  271  which is further fluidly connected with a first flow channel  234 . The air channel is fluidly connected with a vent  225  which is arranged to also provide a reservoir  275  capable of containing a volume of liquid. The reservoir  275  is formed as a serpentine channel extending from an air inlet node  272  to a serpentine end  276 . A second hollow spike (not visible) protruding from the backside of the transfer unit  205  is adapted to establish fluid connection with a powder container (not shown) when the powder container is received in a second port (not visible). This spike has a single channel (not visible) which is fluidly connected with a mixing node  273  which is in turn fluidly connected with, respectively, a second flow channel  235  and a third flow channel  236 . The third flow channel  236  comprises a constriction  222  for controlling the flow rate of the mixed product during transport from the second container to a syringe (not shown), when the syringe is attached to the transfer unit  205 . A connecting piece  256  at a third port  213  provides an interface for coupling with such a syringe.  FIG. 9  also discloses a bore  280  adapted to house the user operable flow control member (not shown). 
         [0135]      FIG. 10  shows a perspective view of a sealing cover  277  adapted for permanent attachment, e.g. by gluing or welding, to the top face  207  to seal the various channels in the transfer unit  205 . The sealing cover comprises a plate  278  having a configuration which enables a complete coverage of the channels in question. A small hole  279  is arranged in the plate  278  in such a manner that when the plate  278  is attached to the top face  207  the hole  279  is positioned just above the serpentine end  276 . 
         [0136]    In use, when the transfer unit  205  is coupled to the container unit  26  an excess pressure may build up inside the first container  2  during penetration of the membrane  6  by the first hollow spike. If this happens a small volume of diluent  8  will be forced through the air channel and into the vent  225 . However, as the vent  225  is formed to comprise the reservoir  275  the diluent  8  will merely accumulate in the reservoir  275 . When a negative pressure is generated in the first container  2 , as a consequence of the plunger  21  in the syringe  20  which is coupled to the third port  213  being retracted, air will be sucked into the vent  225  through the hole  279  above the serpentine end  276  and will enter the first container  2  along with the accumulated volume of diluent  8 . From here this volume of diluent  8  will simply be evacuated along with the rest of the diluent  8  into the first flow channel  234  and further on to the syringe  20 . The arrangement of the reservoir  275  as a serpentine channel, whereby a tortuous path is provided from the air inlet node  272  to the serpentine end  276 , and the position of the hole  279  above the serpentine end  276  minimise the risk that the escaped diluent  8  will leak out of the transfer unit  205  through the hole  279 . 
         [0137]      FIGS. 11   a  and  11   b  show perspective views of an alternative embodiment of a third flow control member, for use in a transfer unit of the mixing system  1 , having the same function as the above described. Dial plug  219  comprises a conical plug body  240  and a dial  241  intended for manipulation of the dial plug  219  by a user of the mixing system  1 .  FIG. 11   a  shows a first channel segment  242  in the plug body  240  which channel segment  242  constitutes a part of the first fluid pathway  14  fluidly connecting the first port  11  and the third port  13  as well as of the second fluid pathway  15  fluidly connecting the third port  13  and the second port  12 , when the dial plug  219  is in a first position. The first channel segment  242  consists of a main portion  244  and a first branch  245 . During transport of material from the first port  11  to the third port  13  the material flows through the first branch  245  and the main portion  244 , whereas during transport of the material from the third port  13  to the second port  12  the material only flows through the main portion  244  (in the opposite direction of the flow to the third port  13 ).  FIG. 11   b  shows a second channel segment  243  in the plug body  240  which channel segment  243  constitutes a part of the third fluid pathway  16  fluidly connecting the second port  12  and the third port  13 , when the dial plug  219  is in a second position. The channel segments  242 ,  243  are provided between lips  247  of material which has been bound to the plug body  240 , e.g. by two-component moulding, and which provides for a fluid tight fit of the plug body  240  in the transfer unit housing. The lips  247  are of a softer, more flexible material than the plug body  240  which further results in a low friction interface between the plug body  240  and the transfer unit housing, making the third flow control member  219  easy to operate even for a user with limited dexterity. 
         [0138]      FIG. 12  shows a cross sectional side view of the transfer unit  205  and illustrates a stop arrangement according to an aspect of the invention. In the figure a syringe  220  (only the distal most portion is shown) has been attached to the connecting piece  256  by mating an inner screw thread  262  of a syringe collar  263  with an outer screw thread  261  of the connecting piece  256 . The syringe  220  has thereby been screwed onto the connecting piece  256  to a point where the collar  263  abuts a contact face  286  of an outer cover  285  adapted to protect the top face  207  of the transfer unit  205 . The contact face  286  thus provides a stop for further mounting movement of the syringe  220  relative to the housing  210 . Hereby, it is ensured that the user does not risk accidentally breaking the conical open end portion of the syringe  220  by excessively forcing the syringe  220  onto the connecting piece  256 , e.g. due to an uncertainty of whether proper attachment has been attained. 
         [0139]    In the above description of the exemplary embodiments, the different structures providing the desired relations between the different components just as the means providing the described functionality for the different components of a transfer system have been described to a degree to which the concept of the present invention will be apparent to the skilled reader. The detailed construction and specification for the different structures are considered the object of a normal design procedure performed by the skilled person along the lines set out in the present specification. 
         [0140]    The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.