Claims for Patent: RE43834

Summary for Patent: RE43834

Title:	Injection syringe
Abstract:	The present invention provides an injection syringe comprises a housing including a holder for containing a cartridge of medicine, a piston rod with a non-circular cross-section having an outer thread, a piston rod drive, a one way coupling having an annular ring of internal ratchet notches, which annular ring can be integral with the housing, and a pawl having at least a pair of resilient arms each having a free end.
Inventor(s):	Steenfeldt-Jensen; Soren (Hornback, DK), Hansen; Steffen (Hillerod, DK)
Assignee:	Novo Nordisk A/S (Bagsvaerd, DK)
Application Number:	10/442,855
Patent Claims:	1. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to the cartridge.[.,.]..Iadd.;.Iaddend. a piston rod having a not circular cross-section and an outer thread.[., and.]..Iadd.;.Iaddend. a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including a first part rotatably mounted within said housing and mating with the not circular cross-section of said piston rod, and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a .[.self-locking.]. thread connection, wherein rotation of said first part in a first direction relative to said second part drives said piston rod in a distal direction; and a one-way coupling comprising: a) an annular ring of equally spaced internal ratchet notches situated on the inside of said housing, which internal notches have a steep front edge and a ramp shaped trailing edge, b) a pawl surrounding said piston rod and having at least a pair of resilient arms, each arm having a free end, said pawl being connected with said first part of said piston rod drive, and c) means situated on said free end of each arm for engaging in the internal ratchet notches of said annular ring, which means abuts said steep front edge of said internal notches, thereby preventing said pawl body from rotating in one direction relatively to said housing, the prevented direction being one by which the piston rod would be transported in a proximal direction.Iadd.; wherein in situation of use, the piston rod does not rotate and advance axially when a dose setting member is rotated in either a clockwise or anticlockwise direction unless an axial force is applied to the pen, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally.Iaddend.. 2. A medication delivery pen according to claim 1, wherein said two or more arms are disposed with the same relative spacing around the circumference of said pawl. 3. A medication delivery pen according to claim 1, wherein said steep front edges of said internal notches on opposite sides of said annular ring are parallel to each other. 4. A medication delivery pen according to claim 1, wherein said arms extend circumferentially from a body portion of said pawl and wherein said means situated on said free end of each arm is the end-surface of the arm lying circumferentially opposite said pawl and abutting said steep front edge of said internal notches. 5. A medication delivery pen according to claim 1, wherein said arms extend circumferentially from said pawl body and wherein said means situated on said free end of each arm includes a protrusion. 6. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to said cartridge.[.,.]..Iadd.;.Iaddend. a piston rod having a not circular cross-section and an outer thread.[., and.]..Iadd.;.Iaddend. a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including .[.a first part having an internal thread mating the thread of said piston rod to form a self-locking thread connection, and a second part integral with said housing and mating with the not circular cross-section of said piston rod,.]. .Iadd.a first part rotatably mounted within said housing and mating with the not circular cross-section of said piston rod so that the piston rod rotates with the first part but the piston rod may move axially independent of the first part, and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a thread connection .Iaddend.wherein rotation of said first part in a first direction relative to said second part drives the piston rod in a distal direction; .[.and.]. a one-way coupling comprising: a) an annular ring of equally spaced internal ratchet notches situated on the inside of said housing, which internal notches have a steep front edge and a ramp shaped trailing edge, b) a pawl surrounding said piston rod and having at least a pair of resilient arms, each arm having a free end, said pawl being connected with said first part of said piston rod drive, and c) means situated on said free end of each arm for engaging in the internal ratchet notches of said annular ring, which means .[.abuts.]. .Iadd.engages in said internal notches by (i) abutting .Iaddend.said steep front edge of the internal notches, thereby preventing said pawl body .Iadd.and said first part of said piston rod drive .Iaddend.from rotating in .[.one direction relatively to said housing.]. .Iadd.a direction opposite to said first direction.Iaddend., the prevented direction being one by which the piston rod would be transported in a proximal direction.Iadd., and (ii) resting along the ramp shaped trailing edge of the internal notches, thereby providing an initial reluctance that has to be overcome by a sufficiently strong rotational torque before said pawl body and said first part of said piston rod drive can rotate in the first direction; and a dose setting mechanism comprising a not self locking thread connection along which an injection button by rotation of a dose setting element relative to the housing is screwed out from the proximal end of the housing and which thread connection by axially returning the injection button in a distal direction back into the housing transforms said axial movement to a rotational torque on the first part of the piston rod drive and said pawl causing said first part to rotate in a the first direction, provided that the rotational torque is strong enough to overcome the initial reluctance provided by the one-way coupling; wherein a set dose may be reduced in size without having to axially pull apart any parts of the pen.Iaddend.. 7. A medication delivery pen according to claim 6, wherein said two or more arms are disposed with the same relative spacing around the circumference of said pawl. 8. A medication delivery pen according to claim 6, wherein said steep front edges of said internal notches on opposite sides of said annular ring are parallel to each other. 9. A medication delivery pen according to claim 6, wherein said arms extend circumferentially from a body portion of said pawl and wherein said means situated on said free end of each arm is the end-surface of the arm lying circumferentially opposite said pawl and abutting said steep front edges of said internal notches. 10. A medication delivery pen according to claim 6, wherein said arms extends circumferentially from said pawl body and wherein said means situated on said free end of each arm includes a protrusion. 11. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to said cartridge.[.,.]..Iadd.;.Iaddend. a piston rod .Iadd.that is rotatable during injection of the medication, said piston rod .Iaddend.having a not circular cross-section and an outer thread.[., and.]..Iadd.;.Iaddend. a piston rod drive for .Iadd.rotating the piston rod during injection, thereby .Iaddend.driving said piston rod in a distal direction inside the cartridge, said piston rod drive including a first part having an internal thread mating the thread of said piston rod to form a .[.self-locking.]. thread connection, a second part mating with the not circular cross-section of said piston rod, wherein said first and second parts are rotatable relative to one another to drive the piston rod in an axial direction; and a one-way coupling comprising: a) an annular ring member of equally spaced internal ratchet notches, and b) a pawl member having at least a pair of resilient arms, each arm having a free end for engaging said ratchet notches so as to allow rotation between said ring and said pawl in a first rotational direction and prevent rotation between said ring and said pawl in a second rotational direction, wherein said members are coupled between said housing and said piston rod drive such that rotation between said members in said first rotational direction causes the piston rod to move in a distal direction, and such that said members prevent movement of said piston rod in said proximal direction.Iadd.; wherein in situation of use, the piston rod does not rotate and advance axially when a dose setting member is rotated in either a clockwise or anticlockwise direction unless an axial force is applied to the pen, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally.Iaddend.. .Iadd.12. An injection device comprising: a housing for holding a cartridge of medication, the housing having a distal end and a proximal end; a threaded piston rod that is rotatable during injection of the medication, said piston rod having a not-circular cross-section; a piston rod drive for rotating said piston rod during injection, thereby driving said piston rod in a distal direction inside the cartridge, said piston rod drive comprising: a first rotatable part that engages the not-circular cross-section of the piston rod so as to allow rotation of the piston rod to accompany rotation of the first part while allowing the piston rod to move proximally and distally with respect to the first part; a second part that engages the threads on the piston rod and is fixed in the housing, thereby causing the piston rod to move distally when the piston rod is rotated in a first direction; and a one way coupling for allowing the first part to rotate in the first direction and thereby drive the piston rod to move distally but prevents the piston rod from rotating in a second direction that would cause the piston rod to move proximally; wherein in situation of use, the piston rod does not rotate and advance axially when a dose setting member is rotated in either a clockwise or anticlockwise direction unless an axial force is applied to the device, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally..Iaddend. .Iadd.13. A dose injecting apparatus for an injection device that comprises a cartridge of medication from which multiple doses of medication are apportioned and a dose scale drum means for indicating the size of a set dose and for indicating that the apportioned set dose has been delivered; the dose injecting apparatus comprising: a rotatable piston rod that rotates only during injection of medication, wherein the rotatable piston rod comprises a distal portion having an external thread disposed thereon and wherein the piston rod has a proximal portion opposite the distal portion; a first part comprised of a rotatable tubular member that engages and causes the rotatable piston rod to rotate during injection of medication; a second non-rotatable part fixed to a housing, the second part having an internal thread engaging the thread on the distal portion of the rotatable piston rod so that when the rotatable piston rod rotates it screws through the internal thread of the non-rotating second part; and wherein during injection of medication: (i) the piston rod rotates only in one direction, that direction being one that induces the piston rod to move axially in a distal, medication expelling direction and not in a direction that would induce the piston rod to move in a proximal direction, and (ii) the piston rod advances distally to expel medication as a result of the screwed engagement of the thread on the distal portion of the piston rod with the internal thread of the non-rotatable part; wherein in situation of use, the piston rod does not rotate and advance axially when a dose setting member is rotated in either a clockwise or anticlockwise direction unless an axial force is applied to the device, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally..Iaddend. .Iadd.14. The dose injecting apparatus of claim 13, wherein the proximal portion of the piston rod contains a helical thread that is different than the thread on the distal portion and wherein the tubular member has in its interior a corresponding helical thread that engages the helical thread on the proximal portion of the piston rod, and wherein the threaded engagement between the tubular member and the thread on the proximal portion of the piston rod cause the rotation of the piston rod during injection of medication..Iaddend. .Iadd.15. The dose injecting apparatus of claim 13, wherein the tubular member has an interior that engages a non-circular portion of the piston rod so that when the tubular member rotates during injection of medication, it rotates the piston rod..Iaddend. .Iadd.16. The dose injecting apparatus of claim 15, wherein the tubular member has a thread on its outer surface..Iaddend. .Iadd.17. An injection mechanism for expelling a dose of medication from a cartridge contained in a syringe that has a housing, the injecting mechanism comprising: a piston rod that is rotatable during injection of the medication, said piston rod for exerting a force on the cartridge during said injection; a piston rod driver for rotating said piston rod during injection, thereby driving the piston rod in a distal direction inside the cartridge; and a dose dial drum for setting a dose of medication, the dose dial drum axially displaceable relative to the syringe housing in a proximal axial direction by rotating it in a first direction and being axially displaceable in a distal axial direction by rotating it in a second direction opposite the first direction, the dose dial drum being coupleable to the piston rod driver; and wherein the dose dial drum and the piston rod driver are releasably coupleable to each other so that when the dose dial drum and the piston rod driver are coupled together during dose injection, they rotate together but when they are decoupled during dose setting the dose dial drum can rotate independently of and relative to the piston rod drive and wherein during injection of the dose, the piston rod is rotated and screwed through the housing via a threaded engagement between the piston rod and a threaded element fixed relative to the housing; wherein in situation of use, the piston rod does not rotate and advance axially when a dose dial drum is rotated in a dose-reducing direction unless an axial force is applied to the mechanism, wherein when the axial force is applied to press an injection button home, the axial force is transformed to result in rotation of the piston rod in a direction which in turn causes the piston rod to advance distally..Iaddend. .Iadd.18. The injection mechanism of claim 17, wherein the dose dial drum rotates toward zero during injection as a result of an axial force being applied to an injection button..Iaddend. .Iadd.19. An injection mechanism for driving a dose of medication from a cartridge in a syringe by transferring an axial force from a user to the cartridge, wherein the injection mechanism comprises: a one piece rotatable piston rod having a first portion having a first thread having a first pitch and a second portion having a second thread having a second pitch that is different than the first pitch, wherein the first and second portions rotate together; a first threaded element fixed with respect to an injection device housing, wherein the first threaded element engages the first thread of the piston rod; and a tube that engages the second thread on the piston rod to form a not self-locking connection so that when the tube is moved axially toward the cartridge without rotating, the tube causes the piston rod to rotate and wherein the piston rod is displaced axially with respect to the housing as the first thread screws within the first threaded element during injection of the medication..Iaddend. .Iadd.20. The injection mechanism of claim 19, further comprising a dose scale drum that is threadedly engaged with a second thread element that is fixed to the housing so that when an axial force is applied, the force induces rotational movement of the dose scale drum and wherein the tube may move axially without rotating while the dose scale drum is rotated..Iaddend. .Iadd.21. The injection mechanism of claim 20, wherein the tube is prevented from rotating relative to the housing during injection of medication and wherein the dose scale rotates to a zero position during injection..Iaddend. .Iadd.22. The injection mechanism of claim 21, wherein the dose scale drum is journalled on the tube..Iaddend. .Iadd.23. The injection mechanism of claim 21, wherein tube is locked against rotations during an injection..Iaddend. .Iadd.24. The injection mechanism of claim 20, further comprising a first button for setting a dose and a second button for receiving the force that is transferred to the cartridge from a user..Iaddend. .Iadd.25. The injection mechanism of claim 22, wherein the piston rod has at least two different cross-sectional shapes..Iaddend. .Iadd.26. The injection mechanism of claim 20, further comprising an injection button for being pressed during injection and for receiving the force necessary to drive the medication from the cartridge..Iaddend. .Iadd.27. The injection mechanism of claim 24, wherein a user can reduce a wrongly set too large dose without injecting medication by merely rotating the first button in a direction opposite that which is used to set a dose..Iaddend. .Iadd.28. The injection mechanism of claim 26, further comprising numbers disposed on the dose scale drum that are indicative of the size of a set dose and further comprising a window through which the numbers are viewed..Iaddend. .Iadd.29. The injection mechanism of claim 27, wherein the dose scale drum is threadedly engaged with the second thread element via a non self-locking connection that allows the dose scale drum to rotate toward zero during injection and while the second button is pressed and while the tube is moved axially..Iaddend. .Iadd.30. An injection mechanism for driving a dose of medication from a cartridge in a syringe, the injection mechanism comprising: a rotatable one piece piston rod having first and second threaded sections that are distinct and have different pitches but wherein the first and second sections rotate and translate in unison; a drive tube having a threaded interior portion for engaging the second thread on the piston rod; wherein the piston rod is threadedly connected to a first threaded element that is rotationally and axially fixed with respect to a syringe; wherein the tube engages the second piston rod thread and forms a non self-locking connection between the tube and the piston rod's second thread; and wherein during injection the tube moves axially without rotating and thereby induces the piston rod to rotate which in turn causes the piston rod to advance axially by screwing through the first threaded element..Iaddend. .Iadd.31. The mechanism of claim 30, wherein the mechanism further comprises a dose scale drum that rotates to a zero position during injection and wherein prior to injection the size of a set dose may be reduced without injecting medication by merely rotating the dose scale drum in a direction opposite that which is used to set a dose and wherein the dose scale drum's rotation to zero during injection is induced by an axial pressing force exerted by a user on an injection button during injection..Iaddend. .Iadd.32. The mechanism of claim 31, wherein the dose scale drum rotates about the tube during injection of medication without being rotationally coupled to the tube during injection of medication..Iaddend. .Iadd.33. The mechanism of claim 32, wherein the dose scale drum is threadedly engage with a second threaded element that is also rotationally and axially fixed..Iaddend. .Iadd.34. An injection mechanism for injecting multiple doses of medication from a syringe, the mechanism comprising a rotating piston rod that, when it rotates, transmits a force to a cartridge containing medication, the force being large enough to expel medication from the cartridge, the piston rod comprising at least two different threaded sections having different threaded configurations and different pitches but wherein both sections are fixed together so that they rotate in unison..Iaddend. .Iadd.35. The mechanism of claim 34, further comprising a scale drum having a numerical scale and a helical thread, wherein the numerical scale is visible to indicate a dose size that a user has set and wherein the mechanism expels a dose equal to that which is indicated on the scale during an injection..Iaddend. .Iadd.36. The mechanism of claim 35, wherein the scale is visible in a window and wherein after a dose is set by rotating a dose setting member, the dose size may be reduced by mere rotation of the dose setting member in a direction opposite the dose setting direction without injecting medication..Iaddend. .Iadd.37. The mechanism of claim 36, wherein the scale drum rotates toward a zero dose size during an injection as a result of its helical thread and wherein the piston rod rotates and moves in a distal direction during injection, wherein the rotation of the piston rod is induced by axially moving a tube element that is threadedly engaged with one thread on the piston rod and wherein the distal movement of the piston rod results from the other threaded element on the piston rod engaging a rotationally and axially fixed element..Iaddend. .Iadd.38. An injection mechanism for a syringe comprising a cartridge of medication at one end, an injection button and dose setting button at the opposite end, wherein the injection mechanism comprises a piston rod having a first threaded portion with a first pitch and a second threaded portion with a second pitch, wherein the first and second portions are fixed together so that they rotate in unison, wherein the first threaded portion engages a complimentary first threaded element that is fixed with respect to the syringe and wherein the second threaded portion threadedly engages a tube having a portion having a thread complimentary to the second threaded portion of the piston rod, wherein when the tube moves axially, it induces the piston rod to rotate which in turn causes the piston rod to screw through the first threaded element and move axially..Iaddend. .Iadd.39. The injection mechanism of claim 38, wherein the mechanism comprises a dose scale drum having dose size indicator numbers that are visible through a window in the housing and wherein the drum rotates to a zero position during injection and wherein the tube dose not rotate during injection..Iaddend. .Iadd.40. The injection mechanism of claim 39, wherein the first section of the piston rod threadedly engages the first threaded element, and wherein the first threaded element is fixed to the housing, thereby threadedly connecting the piston rod to the housing..Iaddend. .Iadd.41. The injection mechanism of claim 40, wherein the threaded engagement between the second section of the piston rod and the tube is formed by a helical thread component on the second section of the piston rod engaging a complementary helical element inside the tube and wherein in a dose size is set by rotating a dose setting member in a first direction and wherein, if the dose size needs to be reduced after setting, merely rotating the dose setting member in an opposite direction will reduce the dose size without injecting medication from the syringe..Iaddend. .Iadd.42. An injection device comprising: a housing having a window, a cartridge of medication, a piston rod drive comprising: a piston rod, a first threaded section on the piston rod having a first thread, a second and different threaded section on the piston rod having a different thread, wherein the pitch of the second section is different from the pitch of the first section, a tube, and a dose drum, wherein the first section of the piston rod is threadedly engaged with a first threaded element that is fixed to the housing, wherein the dose drum is threadedly engaged with a second threaded element that is fixed to the housing, wherein the tube is threadedly engaged with the second threaded section of the piston rod, wherein during dose setting the tube rotates relative to the piston rod and moves axially relative to the piston rod, wherein during injection the tube moves axially without rotating to induce rotation of the piston rod which causes the piston rod to screw through the first threaded element toward the cartridge, wherein a dose is set by rotating a dose setting member in a first direction and wherein the size of the set dose may be reduced without injecting medication by merely rotating the dose setting member in a second, opposite direction, wherein the dose drum rotates toward a zero position while a user exerts an axial dose injecting force on the device which drives the tube to move axially, wherein the force is transferred to the cartridge from the user during injection to drive the medication from the cartridge, and wherein the dose drum reaches the zero position upon completion of the injection..Iaddend. .Iadd.43. The device of claim 42, further comprising a dose setting mechanism that comprises one-way coupling that prevents the piston rod from rotating in a direction that would cause it to screw away from the cartridge during injection..Iaddend. .Iadd.44. The device of claim 42, further comprising a dose setting mechanism that prevents the piston rod from being rotating in a direction that would cause it to screw away from the cartridge when the tube is rotated relative to the piston rod to set a dose..Iaddend. .Iadd.45. The device of claim 43, wherein the one-way coupling comprises a ratchet..Iaddend. .Iadd.46. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to said cartridge; a piston rod having a not circular cross-section and an outer thread; a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including a first part rotatably mounted within said housing and mating with the not circular cross-section of said piston rod so that the piston rod rotates with the first part but the piston rod may move axially independent of the first part, and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a thread connection wherein rotation of said first part in a first direction relative to said second part drives the piston rod in a distal direction; a one-way coupling between the first part of the piston rod drive and the housing, the coupling preventing said first part of said piston rod drive from rotating in a direction opposite to said first direction, and providing an initial reluctance that has to be overcome by a sufficiently strong rotational torque on said first part before said first part can rotate in the first direction; and a dose setting mechanism comprising a not self locking thread connection along which an injection button by rotation of a dose setting element relative to the housing is screwed out from the proximal end of the housing and which thread connection by axially returning the injection button in a distal direction back into the housing transforms said axial movement to a rotational torque on the first part of the piston rod drive causing said first part to rotate in the first direction, provided that the rotational torque is strong enough to overcome the initial reluctance provided by the one-way coupling; wherein a set dose may be reduced in size without having to axially pull apart any parts of the pen..Iaddend. .Iadd.47. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to said cartridge; a piston rod having a not circular cross-section and an outer thread; a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including: a first part for imparting rotation to the piston rod but permitting the piston rod to move axially independent of the first part; and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a thread connection; wherein rotation of said piston rod, imparted by the first part, in a first direction relative to said second part, drives the piston rod axially in a distal direction; a one-way coupling comprising: a) an annular ring of equally spaced internal ratchet notches situated on the inside of said housing, which internal notches have a steep front edge and a ramp shaped trailing edge, b) a pawl surrounding and rotationally linked to said piston rod and having at least a pair of resilient arms, each arm having a free end, and c) means situated on said free end of each arm for engaging in the internal ratchet notches of said annular ring, which means engages in said internal notches by (i) abutting said steep front edge of the internal notches, thereby preventing said pawl body and said piston rod from rotating in a direction opposite to said first direction, the prevented direction being one by which the piston rod would be transported in a proximal direction, and (ii) resting along the ramp shaped trailing edge of the internal notches, thereby providing an initial reluctance that has to be overcome by a sufficiently strong rotational torque before said pawl body and said piston rod can rotate in the first direction; and a dose setting mechanism comprising a not self locking thread connection along which an injection button by rotation of a dose setting element relative to the housing is screwed out from the proximal end of the housing and which thread connection by axially returning the injection button in a distal direction back into the housing transforms said axial movement to a rotational torque on the piston rod and said pawl to rotate in a the first direction, provided that the rotational torque is strong enough to overcome the initial reluctance provided by the one-way coupling; wherein a set dose may be reduced in size without having to axially pull apart any parts of the pen..Iaddend. .Iadd.48. A medication delivery pen comprising: a housing having proximal and distal ends and including a holder for containing a cartridge containing a medication to be delivered through a conduit connected to said cartridge; a piston rod having a not circular cross-section and an outer thread; a piston rod drive for driving said piston rod in a distal direction inside the cartridge, said piston rod drive including: a first part for imparting rotation to the piston rod but permitting the piston rod to move axially independent of the first part; and a second part integral with said housing and having an internal thread mating the thread of said piston rod to form a thread connection; wherein rotation of said piston rod, imparted by the first part, in a first direction relative to said second part, drives the piston rod axially in a distal direction; a one-way coupling between the piston rod and the housing, the coupling preventing said the piston rod from rotating in a direction opposite to said first direction, and providing an initial reluctance that has to be overcome by a sufficiently strong rotational torque on the piston rod before the piston rod can rotate in the first direction; and a dose setting mechanism comprising a not self locking thread connection along which an injection button by rotation of a dose setting element relative to the housing is screwed out from the proximal end of the housing and which thread connection by axially returning the injection button in a distal direction back into the housing transforms said axial movement to a rotational torque on the piston rod causing the piston rod to rotate in the first direction, provided that the rotational torque is strong enough to overcome the initial reluctance provided by the one-way coupling; wherein a set dose may be reduced in size without having to axially pull apart any parts of the pen..Iaddend.