United States Patent m
`Sams
`
`[ii] Patent Number:
`[45] Date of Patent:
`
`4,865,591
`Sep. 12,1989
`
`[56]
`
`[54] MEASURED DOSE DISPENSING DEVICE
`[75] Inventor: Bernard Sams, London, England
`[73] Assignee: Hypo guard (UK) Limited,
`Woodbridge, England
`[21] Appl. No.: 205,198
`Jim. 10,1988
`[22] Filed:
`Related U.S. Application Data
`[63] Continuation-in-part of Ser. No. 81,241, Aug. 4, 1987,
`abandoned.
`Foreign Application Priority Data
`[30]
`8713810
`Jun. 12, 1987 [GB] United Kingdom
`A61M 5/315
`[51] Int. a.4
`[52] U.S. a.
`604/186; 604/208;
`604/209; 604/211; 222/287; 222/391
`604/186, 208, 209, 210,
`[58] Field of Search
`604/211; 222/43, 309, 325, 326, 327, 391, 287
`References Cited
`U.S. PATENT DOCUMENTS
`221/47
`1,997,129 4/1935 Taylor et al
`... 128/173
`2,605,763 8/1952 Smoot
`... 128/218
`2,695,023 11/1954 Brown
`206/42
`2,718,299 9/1955 Atwater et al
`222/391 X
`3,141,583 7/1964 Mapel et al
`222/391 X
`3,293,749 12/1966 George et al
`3,348,545 10/1967 Samoffetal
`... 128/218
`3,517,668 6/1970 Brickson
`... 128/218
`... 222/309
`3,894,663 7/1975 Carhart et al
`... 222/391
`3,977,574 8/1976 Thomas
`128/218 C
`4,022,207 5/1977 Citrin
`141/27
`4,099,548 7/1978 Sturm et al
`73/864.18
`4,395,921 8/1983 Oppenlander
`... 222/309
`4,413,760 11/1983 Paton
`4,415,101 11/1983 Shapiro et al
`... 222/288
`433/90
`4,457,712 7/1984 Dragan
`73/864.16
`4,470,317 9/1984 Sabloewski et al
`... 604/208
`4,475,905 10/1984 Himmelstrup
`... 604/211
`4,498,904 2/1985 Turner et al
`... 222/407
`4,526,294 7/1985 Hirschmann et al
`... 604/118
`4,710,172 12/1987 Jacklich et al
`FOREIGN PATENT DOCUMENTS
`222/391
`245198 5/1963 Australia
`0037696 10/1981 European Pat. Off. .
`0143895 6/1985 European Pat. Off. .
`
`222/391
`
`1/1943 Fed. Rep. of Germany .
`730971
`7/1957 France .
`1149735
`9/1958 France .
`1170312
`6/1966 France .
`1445659
`22140 10/1961 German Democratic
`Rep.
`8502546 6/1985 PCT Int'l Appl. .
`293302 9/1953 Switzerland .
`1225495 3/1971 United Kingdom .
`2109690 6/1983 United Kingdom .
`Primary Examiner—Martin P. Schwadron
`Assistant Examiner—Allen J. Flanigan
`Attorney, Agent, or Firm—Willian Brinks Olds Hofer
`Gilson & Lione
`ABSTRACT
`[57]
`The present invention relates to a device for dispensing
`a fluid from a container by means of the axial movement
`of a piston within the container under the influence of a
`plunger moved by the device, which device is adapted
`to receive the container on its forward end and to move
`the plunger axially forward towards or within the con­
`tainer so as to dispense a selected amount of fluid from
`the container upon each actuation of the device, charac­
`terized in that the device comprises:
`i. a disengageable drive mechanism adapted to be recip­
`rocated axially of the device and adapted to positively
`engage the plunger whereby the plunger can be moved
`axially forward by the drive mechanism and to be disen­
`gaged from the plunger to permit relative axial move­
`ment between the drive mechanism and the plunger;
`ii. a disengagement means for selectively engaging or
`disengaging the drive means from the plunger;
`iii. an actuating means, which may be integral with or
`separate from the disengagement means, for actuating
`the disengagement means, which actuation means re­
`quires a positive operation from a user of the device to
`engage and/or disengage the drive mechanism from the
`plunger; and
`iv. means for selecting the extent of travel of the drive
`mechanism so as to control the extent of axial move­
`ment of the plunger upon actuation of the device.
`The invention also provides a device of the invention in
`association with a container of the fluid to be dispensed.
`
`19 Claims, 4 Drawing Sheets
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`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

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`Mylan v. Sanofi
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`U.S. Patent
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`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`U.S. Patent
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`Sep. 12,1989
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`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`U.S. Patent
`
`Sep. 12,1989
`
`Sheet 4 of 4
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`4,865,591
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`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`20
`
`25
`
`30
`
`1
`MEASURED DOSE DISPENSING DEVICE
`
`4,865,591
`2
`of a ratchet as the pawl is retracted and the drive is thus
`not fully disconnected from the ratchet so as to be ready
`for driving the ratchet forward in the next delivery
`, stroke of the device. Firstly, this does not permit a user
`CROSS-REFERENCE TO RELATED
`APPLICATION
`5 to correct any error in setting the extent of retraction
`where this is used to set the amount of fluid to be dis­
`This application is a continuation-in-part of copend­
`pensed. As a result, if too large a retraction has been
`ing U.S. patent application Ser. No. 07/081,241, filed
`permitted, the whole of the incorrect dose must be
`Aug. 4, 1987 now abandoned. The entire text of this
`discharged before the device can be correctly set. Se-
`application Ser. No. 07/081,241 is hereby incorporated
`10 condly, by automatically retracting the pawl in readi­
`by reference.
`ness for the next dose, the device is put into a "cocked"
`The present invention relates to a measured dose
`condition, which means that a user can operate the
`dispensing device.
`device accidentally. Thirdly, we have found that where
`BACKGROUND TO THE INVENTION
`the user is weak he may not depress the push button or
`15 trigger completely or smoothly. This may allow the
`Patients suffering from diabetes often have to inject
`pawl to retract partially or completely before it has
`themselves with frequent doses of insulin and this can be
`reached the full extent of its forward travel. It will
`done using a conventional syringe. However, the pa­
`therefore appear to the user that the full dose has not
`tients often also suffer from side effects of their illness
`been administered and he will then continue to depress
`and are not capable of accurately controlling the opera­
`the push button or trigger for its full travel. As a result,
`tion of such a syringe. It is therefore desirable that they
`the user may administer an overdose, which could be
`should be provided with means for automatically ad­
`fatal.
`ministering an accurately controlled dosage. However,
`GB Specification No. 21096904 A describes a dis­
`the dosage required by different patients can vary over
`quite wide ranges, from for example 2 units of insulin
`pensing mechanism in which the plunger has an external
`per dose to 30 or more units, and it is necessary to en­
`screw thread and fits within an internally screw
`sure that any device is capable of selecting a range of
`threaded fixed sleeve. The plunger is rotated by a drive
`dosages simply and accurately.
`cap so as to move the plunger axially. The cap incorpo­
`Many forms of dispensing device use a pawl and
`rates a pawl and ratchet mechanism so that the cap can
`ratchet mechanism to connect a push button or trigger
`be rotated in one direction without rotating the plunger,
`operated by the user to a plunger driving a piston in the
`but rotates the plunger in the opposite direction. The
`barrel of the syringe or a cartridge carried by the de­
`volume of fluid to be dispensed in set by rotating the cap
`vice. This achieves a positive drive on the forward
`in the first direction the desired amount from a zero
`stroke, but allows the button or trigger to be retracted,
`point. The dose is dispensed by rotating the cap in the
`for example under the bias of a return spring, with the
`opposite direction back to the zero. Whilst this device is
`pawl riding over the teeth of the ratchet, in readiness
`not automatically returned to the "cocked" position
`for the next actuation of the device. The drive between
`after each use, it is cumbersome to use, especially when
`the pawl and the ratchet is thus never fully disengaged.
`the user is injecting fluid single handedly into his poste­
`Typical of such devices are those described for example
`rior. Furthermore, since the drive between the cap and
`in U.S. Pat. Nos. 1997129, 2605763, 2718299, 3517668,
`40 the plunger is not fully disengaged, the device can be
`3894663, 3977574, 4022207, 4099549, 4415101, 4457712
`pumped by repeated rotation and contra-rotation of the
`and 4470317; French Patent Specifications Nos.
`cap. It has been proposed in PCT Published Application
`1445659, 1170312 and 1149735; and German Patent
`No. WO 85/02546 to operate a syringe using an electric
`Specification No. 730971.
`stepper motor to advance the plunger in the syringe a
`Where any provision is made for selecting the volume
`45 predetermined amount. This may reduce the risk that an
`of fluid to be dispensed, this is usually by way of stops
`incorrect or excessive dose is dispensed, but such a
`limiting the depression of the push button or trigger
`device is expensive and cumbersome and is not suited
`operating the device.
`for carriage upon the person or for general use.
`European Patent No. 0037696 describes a device in
`It has further been proposed, for example in Swiss
`which positive drive between the plunger and the push
`50 Patent No. 293302 and U.S. Pat. No. 2695023, to use an
`button is achieved by having ratchet teeth along the
`automatically engaging latch to limit the travel of the
`length of the plunger into which engage the co-operat­
`plunger of a syringe to the distance between adjacent
`ing teeth of a spring loaded pawl member carried on an
`notches on the plunger into which the latch engages.
`axially operated push member extending through the
`This permits the user to dispense only single doses.
`.
`rear end of the device. A stop engaging in a slot in the
`,
`push member limits the extent of travel of the push 55 Where multiple doses are required, the user must re­
`member and the volume of fluid to be dispensed is se-
`peatedly actuate the latch and must count and remem-
`lected by withdrawing the push member the required
`^er the number of times he has actuated the latch. This
`distance from the forward extreme of its travel with the
`^ awkward and often a user cannot remember correctly
`pawl riding over the teeth of the ratchet. The dose is
`the number of times he has operated the latch, leading
`administered by depressing the push member which 60 to inaccurate doses,
`A further problem with the above devices is that a
`carries the plunger with it. Once the plunger has
`user cannot determine accurately how much insulin or
`reached the forward extreme of its travel and the con-
`other medicament is left in the body of the syringe or
`tainer has been emptied, the pawl automatically disen­
`cartridge and hence whether he can achieve the next
`gages from the plunger to allow the plunger to be fully
`retracted to permit a new container to be fitted to the 65 dosage completely from that syringe or cartridge or
`whether he must use a fresh one to achieve the complete
`device.
`In the above forms of device, an essential feature of
`dose. Mere visual inspection through the transparent
`the design is that the pawl is free to ride over the teeth
`wall of the container is usually too inaccurate to be able
`
`35
`
`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`4,865,591
`4
`3
`The medicament is preferably contained in a car­
`to distinguish between, say, 8 and 14 units of insulin
`tridge, notably one with a comparatively short wide
`remaining in the container and some more accurate
`body, typically from 0.3 to 3 cms external diameter and
`guide is required.
`from 3 to 7.5 cms long. The cartridge has one end
`As a result, a need still exists for a simple measured
`dose dispensing device which can deliver accurately 5 closed by a transverse membrane or wall, the other
`being closed by the axially moveable piston. If desired,
`controlled but variable doses of fluid and which can be
`the one end can carry a hypodermic needle or the like
`used single handedly by weak or infirm users without
`already in position, or this can be provided as a separate
`the risk of "pumping" the device to administer an over­
`component which is secured in place when the car­
`dose.
`lo tridge is mounted on the device of the invention. For
`SUMMARY OF THE INVENTION
`convenience, the invention will be described hereinafter
`in terms of the use of a cartridge of insulin.
`Accordingly, the present invention provides a hand
`The cartridge may be mounted at the forward end of
`portable device for dispensing a fluid from a container
`the device by any suitable means, for example as a push,
`by means of the axial movement of a piston within the
`container under the influence of a plunger moved by the 15 screw, bayonet or other fit within an axial socket at the
`forward end of the device. The socket can contain other
`device, which device is adapted to receive the container
`components of the device which are to co-operate with
`at its forward end and to move the plunger axially for­
`the cartridge, for example a mechanism for preventing
`ward toward or within the container so as to dispense a
`the plunger from moving rearwardly as described later.
`selected amount of fluid from the container upon each
`actuation of the device, characterised in that the device 20 It is particularly preferred to provide an internal cir-
`cumferential annular shoulder or series of projections
`comprises:
`which act as a stop against which the rim of the car­
`i. a disengageable drive mechanism adapted to be
`tridge seats when fully home in the socket, thus cor­
`reciprocated substantially co-axially of the device and
`rectly positioning the cartridge axially in the device.
`adapted to positively engage the plunger whereby the
`The cartridge is preferably mounted within a detach­
`plunger can be moved axially forward by the drive 25
`able housing which is a screw or other fit into the de­
`mechanism and adapted to be disengaged from the
`vice, for example into the axial socket. The use of such
`plunger to permit relative axial movement between the
`a housing aids correct mounting of replacement car­
`drive mechanism and the plunger;
`tridges in the device. By making the housing from a
`ii. a disengagement means for selectively engaging
`and/or disengaging the drive mechanism from the 30 clear plastic material, a user can readily observe the
`movement of the piston within the cartridge and can
`plunger;
`assess the amount of fluid in the cartridge. The housing
`iii. an actuation means, which may be integral with or
`also provides a measure of protection to the cartridge,
`separate from the disengaging means, for actuating the
`both physical and against pathogenic organisms and
`disengagement means, which actuation means requires
`a positive operation from a user of the device to engage 35 other possible contamination,
`Where such a housing is used, the needle end of the
`and/or disengage the drive mechanism from the
`cartridge can project through a terminal aperture in the
`plunger; and
`housing or that end of the housing can be closed and can
`iv. means for selecting the extent of travel of the drive .
`carry a needle or other outlet integrally therewith
`mechanism so as to control the extent of axial move-
`40 which projects axially inwardly into the housing to
`ment of the plunger upon actuation of the device.
`penetrate the membrane at the end of the cartridge.
`The device of the invention reduces many of the
`The cartridge houses the piston which is to be moved
`problems associated with designs proposed hitherto by
`by the plunger. This piston can be of conventional de­
`using a drive mechanism which can be disengaged from
`sign and will usually form part of the cartridge as com­
`the plunger at any point during its travel, notably for
`the dose selection step. This allows errors in the dose 45 mercially available. The plunger acts on the piston and
`the piston can carry a socket or other recess to receive
`selection to be corrected before the drive is re-engaged.
`and locate the head of the plunger. In some cases, the
`The drive mechanism is locked onto the plunger for the
`plunger can be affixed to the piston and will form part
`forward stroke of the mechanism, so that the plunger or
`of the cartridge as supplied, in which case the plunger
`drive mechanism cannot be partially retracted during
`the forward stroke, which reduces the risk of adminis- 50 will extend into the device when the cartridge is
`mounted on the device. However, it is preferred that
`tering an overdose. The engagement and/or disengage­
`the plunger form part of the device rather than of the
`ment of the drive mechanism requires a positive opera­
`cartridge and, for convenience, the invention will here­
`tion to be carried out by the user, so that the device can
`inafter be described with respect to this configuration.
`be left in the de-activated state until the next dose is
`required and cannot be operated until the positive drive 55
`The device typically comprises a substantially cylin­
`drical hollow housing containing the various mecha­
`engagement operation has been carried out. However,
`nisms of the device as described below assembled sub-
`once the dosage has been selected and the drive has
`been re-engaged, the device can readily be used single
`stantially co-axially around the plunger.
`The plunger is preferably a simple elongated rod
`handedly, notably when a dose is being injected into the
`60 which extends axially along the longitudinal axis of the
`user's posterior.
`device and can have a substantially circular, polygonal,
`The container upon which the device of the invention
`is to be used can be a conventional syringe body, but is
`squared or other cross-section as desired. Thus, the
`preferably a generally cylindrical cartridge containing
`plunger may have two or more opposed flatted faces
`the fluid to be dispensed. As indicated above, the inven­
`and/or can have two, or more axial grooves in its sur-
`tion is of especial use in the self-administration of a 65 face to assist angular location of the plunger with re­
`medicament, notably insulin, by a user. For conve­
`spect to the other components.
`nience, the invention will be described hereinafter in
`The plunger can have a plain surface onto which the
`terms of this use.
`drive mechanism acts by a frictional grasp, as when a
`
`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`,
`
`.
`
`•
`
`J •
`
`4,865,591
`6
`5
`However, a particularly preferred form of drive
`Torrington type mechanism is used. However, it is
`mechanism comprises the radially moveable jaws de­
`preferred that the plunger carry an axial series of trans­
`scribed above carried by a split collet assembly jour-
`verse ribs, grooves or teeth which engage with corre­
`nalled on the plunger and having springs or other bias
`sponding teeth carried by the drive mechanism. The
`teeth can extend for substantially the full length of the 5 means for urging the jaws radially outwards. The collet
`or the rear faces of the jaws themselves are acted on by
`plunger, but this need not be the case and the terminal
`an axially reciprocateable push sleeve joumalled upon
`portions of the plunger can have a plain surface. Prefer­
`the plunger. The push sleeve extends rearwardly to
`ably, the teeth are of a saw tooth form with the scarp or
`provide a push button mounting projecting from the
`undercut face of the tooth facing rearwardly. It is pre­
`ferred that the axial distance between adjacent teeth 10 rear
`the device so that depression of the button
`causes the push sleeve and hence the jaws to move
`corresponds to the distance the piston is to move in the
`axially to drive the plunger forward. If desired, the push
`cartridge to dispense a unit dose, for example 1 or 2 ILFs,
`button or-push sleeve can be recessed within the termi­
`of insulin.
`nal portion of the housing so that a user must insert
`The drive mechanism for present use is one which
`can be completely disengaged from the plunger to per- 15 some implement, for example a removable nose cap
`mit relative axial movement between them and so that
`protecting the needle of the cartridge, to be able to
`operate the forward drive.
`there can be no drive between the drive mechanism and
`The drive mechanism is engaged or disengaged by
`the plunger until the drive is positively re-engaged.
`some means which requires a positive operation by the
`However, when the drive mechanism is engaged, it
`20 user of the device so that the drive cannot be acciden-
`locks onto the plunger so that there is substantially no
`tally actuated or over-ridden. Thus, where the plunger
`relative movement between them. A suitable drive
`mechanism may thus incorporate a mechanism which
`hai ^or m°re flatted surfaces, these can be inset
`engages and disengages by radial movement, for exam-
`«dif y from the non-flatted surfaces so that the teeth
`on the jaws, or the balls in a Tomngton type drive
`i « <
`•
`ru ii
`pie:a Tomngton type drive in whichta series of baU or 25
`J as described above) would 8not e™age the
`roller bearings are earned m a tapered cup around he ^ ^ ^ drive can therefore be dis8elf
`d
`plunger. A plug member can be moved axially into.the
`operatively associated
`b rotatin
`the jaws or a
`taper to drive the balls further into the taper and thus
`le the pFush sleeve described above,
`therewith;6for e
`radially mwardly to clamp onto the plunger.
`to align the jaws with the flatted faces, or vice versa, by
`However, a particularly preferred drive mechanism 30 a t
`tial m0Vement. In this position the drive mech-
`compnses two or more jaws arranged substantially
`anism is disengaged and can move relative to the
`symmetrically around the plunger and which can be
`plunger> for example when it is desired to set the dosage
`moved radially mwardly to clamp onto the plunger.
`to be dispensed. The positive operation required by the
`The radially inward faces of the jaws preferably carry
`user js to rotate the push sleeve or the protruding push
`teeth which co-operate with those earned by the 35 bitfton connected thereto with respect to the drive
`plunger to provide a positive locked drive between the
`mechanism and this action has to be reversed before the
`drive mechanism and the plunger when the drive is
`drive can be re-engaged.
`engaged. The teeth on the jaws preferably have a simi­
`However, a preferred form of disengagement mecha­
`lar shape to those on the plunger so that there is a posi­
`nism is a cam or other radially acting mechanism which
`tive fit between them.
`40 moves the drive mechanism radially in and out of en­
`The jaws or other mechanism for making the positive
`gagement with the plunger. Thus, the opposed jaws
`drive connection between the drive mechanism and the
`described above can be moved in and out by a cam
`plunger are preferably carried on a split collet type of
`carried internally on a rotating sleeve portion of the
`structure so that they are joumalled upon the plunger
`housing within which the operating mechanism of the
`and can move axially thereon when disengaged. The 45 device is housed. In this case, the rotatable sleeve sec-
`jaws are normally urged apart by a compression spring
`tion provides both the disengagement means (the inter-
`or other bias means acting radially outwardly so that
`nai cams) and the actuation means (the section of the
`they adopt the disengaged position. In a preferred con-
`housing itself carrying the cams) in a single member,
`struction, the jaws extend transversely to either side of
`The cams acts against the spring or other bias holding
`the plunger and a transverse coil compression spring is 50 the jaws clear of the plunger and brings the jaws into
`held between the jaw extensions at each side of the
`engagement with the plunger. The cams also retain the
`plunger. The springs can be held within a retaining
`jaws in the engaged position, thus locking the drive
`extensible saddle piece formed integrally with each jaw
`connection between the drive mechanism and the
`extension for ease of assembly of the jaw mechanism.
`plunger, until the cams are released by rotating the
`Alternatively, the jaws can be carried via leaf spring 55 sleeve section carrying them. Alternatively, the jaws
`mountings from the collet or from another part of the
`can be tied to the cams so that they are moved radially
`drive mechanism.
`in both directions by the cams without the need for a
`Means are provided whereby a user can move the
`spring bias. A further form of drive disengagement and
`drive mechanism axially to set the dose required and to
`actuation mechanism is an axial or tangentially mounted
`drive the plunger forward. Preferably, the forward 60 lever which is mounted by means of a pivot within the
`drive is by means of a button or the like operatively
`wall of the housing. Raising one end of the lever causes
`. associated with the plunger and extending axially from
`the other end to bear radially against the jaws or other
`the rear end of the device, but others forms of forward
`radially moveable component of the drive mechanism
`drive means can be used. For example, the drive mecha­
`either directly or via an intermediate component so as
`nism or a part operatively associated therewith can 65 to urge them radially inward and into engagement with
`carry a radial arm which extends through an axial slot in
`the plunger.
`Where a rotatable cammed housing section is used, it
`the housing of the device, or a screw type mechanism
`can be used.
`is preferred that the exterior of this section carry mark-
`
`Mylan Exhibit - 1020
`Mylan v. Sanofi
`
`

`

`4,865,591
`8
`7
`axial travel corresponding to the axial distance between
`ings or have an oval cross-section so that a user can tell
`adjacent teeth on the plunger.
`the orientation of the section simply by touch.
`The screw sleeve has means by which it can be ro-
`The device incorporates a dosage selection mecha­
`tated by the user, for example by means of a pin or arm
`nism for selecting the extent of axial travel of the disen-
`gaged drive mechanism so as to control the movement 5 projecting through the wall of the device; or preferably
`by a collar located adjacent the end of the housing. This
`of the plunger and hence the volume of fluid discharged
`is connected to the sleeve through a spline coupling or
`from the cartridge. The drive is then re-engaged and the
`the like to allow relative axial movement between the
`drive mechanism returned to the datum point carrying
`collar and the sleeve.
`the plunger with it. In this way the plunger moves an
`amount which is set by the extent to which the drive 10 The forward movement of the plunger may be
`achieved by returning the dosage selection mechanism,
`mprhankin is retracted from a datum point. Since the
`for example the screw sleeve, to the datum point when
`drive is disengaged during the retraction of the drive
`^e drive is re-engaged. However, this may not be easy
`mechanism, it is possible to correct any over- or under-
`or convenient, notably where this requires the user to
`shoot in the movement of the drive mechanism before
`of the device to achieve this, and it is pre­
`the drive is re-engaged. Also, once the drive has been 15 rotate
`ferred to employ an axial push action, e.g. by means of
`re-engaged, due to the fact that the plunger does not
`the push sleeve as described above. We therefore prefer
`readily move rearwardly, as described below, the user
`that the dosage selection mechanism be demountably
`cannot retract the drive mechanism or the plunger with­
`connected to the drive mechanism so that, when the
`out positively disengaging the drive again. Hence trem­
`20 drive is re-engaged, the connection between the dosage
`ulous or jerky operation of the device will not affect the
`selection and the drive mechanisms is released. This can
`dose to be dispensed.
`be conveniently achieved by providing a latch mecha­
`The datum point for the dosage setting mechanism is
`nism at or adjacent the forward end of the dosage selec­
`preferably a stop determining the extent of forward
`tion mechanism, e.g. the screw sleeve, which latch
`travel of the drive mechanism or a part operationally
`25 mechanism engages the drive mechanism when the
`associated therewith. Thus, the abuttment of the push
`latter is in the disengaged position but which releases
`button driving the push sleeve against the end of the
`the drive mechanism when the latter is in the engaged
`housing can provide that datum point. However, it is
`position. The drive mechanism can then be driven for­
`preferred that the datum point be provided by a stop
`ward independently of the dosage selection mechanism.
`located within the device against which the front face
`30 Suitable latch mechanisms can readily be devised hav-
`of the drive mechanism buts at the forward extreme of
`ing regard to the specific design of the device they are
`.
`,
`.
`.
`.
`, „
`.
`its travel. Conveniently, this stop is also the stop against ^ ^
`'
`which the rim of the cartridge seats when it is fitted to
`The device also comprises means whereby the dosage
`corresponding to a selected extent of retraction of the
`the device, so that the stop serves as the datum point
`both for positioning the cartridge to one side and for the 35 drive mechanism can be observed aurally or visually by
`a user! for example by means of a clicker mechanism.
`dosage selection mechanism on the other.
`Preferably, the push sleeve or the screw sleeve carries
`The dosage selection means can operate axially, as
`markings correlating the dosage with the extent of axial
`when the push sleeve engaging the jaws described
`movement. Where a screw sleeve is used, the markings
`carries one or more external radial projections which
`but against co-operating projections carried by the 40 are carried along a spiral path and are progressively
`brought into register with a window or port in the wall
`housing within which the sleeve reciprocates. Rotation
`0f the housing so that the user can see what dose is to be
`of the housing selects which stops will engage and
`dispensed,
`hence the length of travel of the drive mechanism. Al-
`tematively, the dosage selection mechanism can take
`In order that a user can determine whether or not
`the form of a side arm earned by the push sleeve and 45 sufficient fluid remains within the container to achieve
`a stated amount to be dispensed, it is preferred to pro-
`protruding through a stepped track or aperture in the
`vide a second stop means carried by the plunger, for
`wall of the housing which allows the sleeve to be re-
`example at the rearward end thereof, which is engaged
`tracted for the full length of one axial section of the
`by the drive mechanism or push member as it is re-
`track. The sleeve or a part operadvely associated there-
`with then has to be rotated to allow the arm to move 50 tracted. The second stop will prevent the drive mecha-
`nism or push member from being withdrawn to its full
`transversely into the next section where a larger dose is
`extent if the residual potential travel of the plunger is
`required.
`less than the desired dose. A user will detect resistance
`However, we have found that a screw mechanism
`to operation of the dosage selection mechanism or will
`provides a particularly effective and accurate means for
`retracting the drive mechanism. Thus, for example, the 55 notice when the spline drive between collar 10 and the
`screw sleeve is over-ridden when this occurs. The user
`dosage selection means utilises a screw sleeve jour-
`can then tell from the dose indicated as described above
`nailed upon the push sleeve. The screw sleeve carries an
`whether there is sufficient medic