Abstract:
A device for the automatic injection of doses of a drug compound is described. The device has a sliding sheath which, when depressed with its front end against the injection site, interacts with cam means to activate triggering of a plunger, thus controlling delivery of a drug dose. Plunger guide means are provided for controlling the triggering sequence and means for arming the device in the dose delivery condition. Automatic needle re-sheathing and resetting of a lock-out condition after each dose is delivered are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is the US national stage of International Patent Application PCT/EP2012/067438 filed on Sep. 6, 2012 which, in turn, claims priority to Italian Patent Application FI2011A000194 filed on Sep. 8, 2011. 
     FIELD OF THE INVENTION 
     The present invention relates generally to devices for the injection of medicaments and more precisely relates to a device for the automatic injection of medicaments especially a medicament for allergic emergencies, such as epinephrine or adrenaline, according to a requested time sequence. In particular, the invention refers to a device for the automatic injection of two doses of a medicament at two successive times. 
     BACKGROUND OF THE INVENTION 
     Many devices of the above mentioned type allowing a patient to self-administer one or more (generally two) doses of a medicament are known. U.S. Pat. No. 6,575,939 discloses an autoinjector device comprising a syringe housed in a casing formed by an inner part and an outer part capable of sliding in relation to each other. By pressing the end of the inner part (the needle outlet end) against the patient&#39;s skin at the injection site, the outer part slides forward along the inner part, thus unlocking a push-button. By depressing the button, the syringe and the relevant plunger are triggered to first thrust in the needle and then deliver the medicament. The needle retraction in the casing is obtained by stopping pressing the outer part end against the skin. This auto-injector allows a single dose of medicament to be administered. 
     An autoinjector device for automatic administering a single dose of a medicament is also known from U.S. Pat. No. 4,031,893. The autoinjector is equipped with an unlocking device with a deformable member for the driving device. The syringe plunger is axially connected to a rod comprising four flexible axial arms having a toothed end engaged on the edge of an opening formed on a cap placed at the end of the syringe housing. Cap sliding causes the arm ends to deform and their teeth to release from the opening edge. In this way the driving device is triggered. The autoinjector according to this document also comprises a safety device to prevent accidental deformation of the arm ends and triggering of the driving device, consisting of an insert centrally extending from the cap and capable of coming between the rod arms to prevent them from bending. 
     EP700307 discloses a two-dose autoinjector allowing the automatic delivering of a first dose of a medicament and the manual administration of a second dose. The autoinjector device according to this patent foresees the use of a syringe housed slidably in a tubular housing in two parts that can be separated to allow positioning of the syringe containing two doses of the medicament to be delivered and removal after use. The sliding of the syringe in the housing to penetrate the needle and inject the medicament is operated by an actuator movable between an armed position and an extended position. A releasable locking device is provided to limit the syringe plunger sliding to an extent corresponding to the volume of the first dose. The syringe is mounted in the tubular housing in a movable way to enable the locking device to be removed after the first dose is delivered and the plunger drive means to be armed again, if the second dose is to be automatically administered, or the syringe to be removed, if the second dose is to be manually administered. Furthermore the drive means is provided with a safety lock formed by a member engaging with a deformable pin of the drive means to keep it in a deformed condition, thereby preventing it to trigger. An autoinjector of this type is commercially available under the trade mark Twinject® and allows the first dose to be administered automatically, but the second dose must be manually administered. 
     The autoinjector according to EP651662 is designed to carry out a sequence of injections from a single syringe that is capable of performing a limited sliding movement in a tubular housing. The syringe has a plunger to deliver doses of a medicine through the needle and spring drive means engage with a plunger rod and, once they are armed, retain the rod in a first position, while, when they are triggered, cause the rod to move forward and this causes first the syringe sliding and needle projection and then a controlled sliding of the plunger to deliver a medicine dose. Manual arming means are provided and means to trigger again the spring drive means. 
     The plunger rod has a toothed profile on which a catch of the drive means engages and the syringe is housed in a bushing capable of moving in a limited way in the tubular housing and provided with a further catch that is also engaged with the toothed profile of the rod. When the device is armed by the manual arming means, both the drive means and the bushing in which the syringe is placed are displaced toward the rear end of the tubular housing, the two catches engaging with the toothed profile of the rod. An axial groove connection between the bushing and the drive means allows a further sliding between the catch integral to the drive means and the toothed profile of an extent equal to the pitch of the profile. When the device is triggered, first the drive means cause the syringe bushing to slide up to a front stop and then the rod start sliding relative to the bushing catch for an extent corresponding to the profile pitch, whereby the displacement of a volume of medicine is enabled together with its deliver through the needle. 
     There is a strong need for an injector device for the automatic injection of a medicament in two successive doses which is user-friendly and is easier to manufacture as compared to the conventional devices. The object of the present invention is therefore to meet these requirements by providing a medicament autoinjector device capable of enabling the patient to self-administering two successive doses of a medicament in the easiest possible way, thus sparing the patient of performing potentially dangerous, complex dismounting/re-arming operations. 
     SUMMARY OF THE INVENTION 
     The general object of the present invention is to provide a device for the automatic injection of multiple discrete nominal volumes of a drug compound, especially two doses of the drug compound from the same syringe. 
     A particular object of the present invention is to provide a device of the above mentioned type in which the automatic injection of discrete nominal volumes of drug compound is achieved by combination of rotational and translational movements of device components. 
     Another object of the present invention is to provide a device of the above mentioned type in which the automatic injection of a prescribed dose is triggered by use of a patient activated linear sliding of a component in combination with the angular displacement of plunger means being guided by cam means in an encapsulated chassis. 
     It is a further object of the present invention to provide a device of the above mentioned type with an automatic sheathing lock-out feature for needle protection and prevention of inadvertent triggering of the device before a dose is selected by the user. 
     Still another object of the present invention is to provide a device of the above mentioned type capable of automatic re-sheathing the needle and resetting the lock-out condition after a dose is injected. 
     Another object of the invention is to provide a device of the above mentioned type in which the triggering function and the driving function are integrated on same support to lower tolerances, increase reliability and reduce the number of components of the device, this also resulting in a simple device structure and production cost reduction. 
     Still another object of the invention is to provide an autoinjector device of the above mentioned type in which the production and assembling thereof are easy to carry out. 
     The above objects are achieved with the device for the automatic injection of doses of a medicament according to the present invention, whose main features are set forth in the attached claim  1 . Further important features are set forth in the dependent claims. 
     According to an important aspect of the device for the automatic injection of doses of a drug compound according to the present invention, the axial movement of a sliding sheath, caused by the user by depressing its front end against the injection site, causes the angular displacement of cam trigger means, which, in cooperation with stepped guide means, controls the movement of plunger means of a syringe group and thus the delivery of prefixed doses of a drug compound. The movement of the plunger means is produced by axially operating first elastic means, while the axial movement of the sliding sheath is hindered by second elastic means that reinstate the initial needle covering condition of the sheath when the pressure action ceases. To make the device ready for the delivery of a dose, device arming means are provided which, when operated, unlock the sheath axial sliding. The lock-out condition, as well as the needle retraction in the sliding sheath, are automatically reinstated when the pressure ceases under the action of the second elastic means. 
     According to another important aspect of the invention, the cam trigger means are formed on the same support, axially pivotable, as cam drive means with which the sliding sheath interacts to control the triggering of the plunger means of the syringe group. 
     According to a further aspect of the invention the means allowing the device to be kept in a rest state are formed on the support of the cam trigger means and the cam drive means and are unlocked as a result of a rotation of a dose selection knob pivotally mounted on the device body and temporarily connected to the support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features, as well as the advantages of the auto-injector device according to the invention will be apparent from the following description of an exemplifying, non-limiting embodiment thereof with reference to the attached drawings, in which: 
         FIG. 1  is a perspective assembly view of the autoinjector device according to the present invention; 
         FIG. 2  is a perspective partially exploded view of the device of  FIG. 1 ; 
         FIG. 3  is a fully exploded view of the device of  FIG. 1 ; 
         FIG. 4  is a longitudinal section of the device of  FIG. 1 ; 
         FIG. 5  is a longitudinal section of the device of  FIG. 1  taken along lines V-V of  FIG. 4 ; 
         FIG. 6  is a detail view of the connection between the dose selection knob and the plunger rod in the device of  FIG. 1 ; 
         FIG. 7  is an exploded view of the detail of  FIG. 6 ; 
         FIG. 8  is an axial perspective view of the dose selection knob; 
         FIG. 9  is a top perspective partial view of the plunger rod; 
         FIG. 10  is a perspective view of the outer body of the device of  FIG. 1 ; 
         FIG. 11  is a longitudinal section of the outer body of  FIG. 10 ; 
         FIG. 12  is a top perspective partial view of the outer body of  FIG. 10 ; 
         FIG. 13  is an assembly view of the syringe group of the device of the invention; 
         FIG. 14  is a perspective view of the operative connection between the cam sleeve and the sliding sheath in the device of the invention; 
         FIG. 15  is an axial side view of the sliding sheath; 
         FIG. 16  shows a sectional view of the sliding sheath taken along lines XVI-XVI of  FIG. 15 ; 
         FIG. 17  is a front perspective view of the sliding sheath of  FIGS. 15 and 16 ; 
         FIG. 18  is an axial side view of the cam sleeve in the device of the invention; 
         FIG. 19  is a rear perspective view of the cam sleeve of  FIG. 18 ; 
         FIG. 20  is a front perspective view of the cam sleeve of  FIG. 18 ; 
         FIG. 21  shows the device armed for the delivery of the first dose and ready for triggering; 
         FIGS. 22   a ,  22   b  and  22   c  are detail views of the device of the invention in position 0 (stored position) and in the position 1 (first dose armed); 
         FIGS. 23   a  and  23   b  show the device of the invention at the beginning and at the end of the first dose delivery step; 
         FIG. 24  shows the device at the resheathing and resetting step; 
         FIGS. 25   a  and  25   b  show the details of the second dose s election step; 
         FIGS. 26   a ,  26   b  and  26   c  show the steps of delivery of the second dose; 
         FIG. 27  is a perspective assembly view of a second embodiment of the autoinjector device according to the present invention; 
         FIG. 28  is a perspective partially exploded view of the device of  FIG. 27 ; 
         FIG. 29  is a fully exploded view of the device of  FIG. 27 ; 
         FIG. 30  is a longitudinal section of the device of  FIG. 27 ; 
         FIG. 31  is a longitudinal section of the device of  FIG. 27  taken along lines XXXI-XXXI of  FIG. 30 ; 
         FIG. 32  is a detail view of the connection between the dose selection knob and the plunger rod in the device of  FIG. 27 ; 
         FIG. 33  is an exploded view of the detail of  FIG. 32 ; 
         FIG. 33   a  is a detail sectional view of the connection between plunger rod and ratchet; 
         FIG. 34  is a top perspective partial view of the plunger rod; 
         FIG. 35  is an axial perspective view of the dose selection knob-ratchet assembly; 
         FIG. 36  is an exploded perspective view of the chassis-outer sleeve assembly forming the outer body of the device of  FIG. 27 ; 
         FIG. 37  is a longitudinal section of the chassis-outer sleeve assembly of  FIG. 36  as assembled; 
         FIG. 38  is a top perspective partial view of the chassis of  FIG. 36 ; 
         FIG. 39  is an assembly view of the syringe group of the device of  FIG. 27 ; 
         FIGS. 40   a, b  and  c  are, respectively, side view, perspective view and longitudinal section view taken along lines  40   c - 40   c  of  FIG. 40   a  of the sliding sheath in the device of the device of  FIG. 27 ; 
         FIGS. 41   a, b  and  c  are, respectively, side view, perspective view and reversed perspective view of the cam sleeve in the device of  FIG. 27 ; 
         FIG. 42  is a perspective view of the operative connection between the cam sleeve and the sliding sheath in the device of  FIG. 27 ; 
         FIGS. 43   a  and  43   b  are detail views of the device of  FIG. 27  in position 0 (stored position) and in the position 1 (first dose armed); 
         FIG. 43   c  is a transverse sectional view of the device in the first dose armed position of  FIG. 43   b;    
         FIGS. 44   a  and  44   b  show the device immediately before and at the triggering point; 
         FIG. 45  shows the device after delivering the first dose during the resheating step; 
         FIGS. 46   a  and  46   b  show the device in the stored position after delivering the first dose and, respectively, in the second dose armed position and ready for delivering the second dose; 
         FIGS. 47   a, b  and  c  are broken-up partial side perspective views showing the device of  FIG. 27  at the second dose armed position of  FIG. 46   b , during the movement toward the triggering point and, respectively at the second dose triggering step; 
         FIGS. 48   a, b  and  c  are detail side views of the bayonet connection of the device according to the second embodiment of the invention before, during and, respectively, at the decoupling step. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 to 5 , the autoinjector device according to the present invention comprises an outer body  1  of tubular shape, in particular a cylindrical body, extending along an axis X and containing the majority of the device components. The outer body is formed by two coaxially aligned body portions  1   a ,  1   b  having different diameter separated by a step  1   c , against which the end of a removable end cap  2  abuts, said cap  2  concealing the front end  3  of the device. In the proximity of the other end, the rear end, of the device angularly spaced reference marks are formed or labelled, for example the numerals 0, 1, 2, indicating a rest o stored state (0), and two operating states (1, 2) of the device, as will be explained later on. In the present description the terms “front”, “rear” and equivalents relate to the part of the device intended for the needle outlet and, respectively, the axially opposed part. It is also stated that in the present description reference is always made to a device for the automatic injection of two doses of a drug, but it is understood that the invention also comprises devices capable of delivering more than two doses of a drug at successive times, through changes and alteration to the device which will be obvious for a person skilled in the art. 
     A dose selection knob  4 , on which a reference indicator  5  is formed, is provided at the rear end of the device. The dose selection knob  4  is axially pivotable relative to the outer body  1  to allow the indicator  5  to align to the reference marks  4  formed thereon. 
     A syringe group, generally indicated at  6 , is housed in the outer body  1 . As shown in  FIG. 13  the syringe group comprises a drug preloaded syringe  7 , with needle  7   a , needle shield  7   b , barrel  7   c  and inner plunger stopper  7   d . In the barrel  7   c  there engages the end of a plunger rod  8 , formed by a tubular element in two parts  8   a  and  8   b  of different diameter. The part  8   a  has a cross section that is in a clearance condition with respect to the inner section of the barrel  7   c  so that it can slide therein, and an end shaped in a way to engage with plunger stopper  7   d  as a result of an axial movement to push it forward on drug delivery. The part  8   b  of the plunger rod  8  has a larger diameter and is formed with internal radial ribs  9  for aligning a power spring  10  extending axially in the plunger rod  8 . The power spring  10  is in a compressed state and abuts against the closed end of the part  8   a  of the plunger rod  8  with one end and against the bottom wall  4   a  of the dose selection knob  4  with its other end. The power spring  10  also winds up around a support rod  11  extending from the same bottom wall  4   a  of the dose selection knob  4  up to the closed end of the part  8   a  of the plunger rod  8 . The arrangement of the power spring  10  between the radial ribs  9  and the part  8   a  of the plunger rod and the support rod  11  helps to minimize buckling of the power spring  10 . 
     In the device stored state the dose selection knob  4  is connected to part  8   b  of the plunger rod  8  by a bayonet connection, shown in particular in  FIGS. 5 to 9 , comprising a pair of substantially L-shaped slots  12  formed circumferentially on part  8   b  at diametrically opposed positions and a pair of retention clips  13  internally projecting from the dose selection knob  4  at diametrically opposed positions. The substantially L-shaped slots  12  comprise a retention slot branch  12   a , extending circumferentially, and a release slot branch  12   b , extending axially up to the edge of the part  8   b  of the plunger rod  8 . When the indicator  5  on the knob  4  is aligned to the reference mark  0 , the two retention clips  13  are engaged in the respective retention slot branches  12   a  of the slots  12 , thus preventing the plunger rod  8  to slide axially. As a result of an angular displacement of the plunger rod relative to the knob  4 , the retention clips  13  slide in the retention slot branches  12   a  until they come into alignment to respective release slot branches  12   b  extending rearward up to the free end of part  8   b  of the plunger rod  8 , thereby allowing the plunger rod  8  to travel forward under the action of the power spring  10 , as will be explained later on about the device operation. 
     Two radial pegs  15  outwardly project from the part  8   b  of the plunger rod at diametrically opposed parts. The two radial pegs  15 , which slide in trigger cam means, provide a means to guide the movement of the plunger rod  8  which controls the drug dose delivery, as will be explained later on. 
     As shown in  FIGS. 4 ,  5  and  6 , the dose selection knob  4  is formed with a perimetrical groove  16  in which an undercut  17  at the rear end of the outer body  1  slidably engages, whereby the dose selection knob  4  is pivotable relative to the outer body  1  so that the selection of the dose to be delivered is allowed. 
     The dose selection knob  4  may rotate in only one direction and to this end the connection between the knob  4  and the outer body  1  comprises means for preventing the rotation in the direction opposite to that of dose selection. These means comprise a pair of ratchet legs  18  (see  FIGS. 6 and 7 ) perimetrically extending from the edge of the knob  4 , suited to slidably abut, when the knob  4  is rotated, on an indexing ramp surface  19  defining two ramp steps  19   a, b  (only one shown in  FIGS. 10 and 11 ). When the legs  18  slide on the ramp surface  19 , first they flex and then, once the ramp has overcome, they trigger at the ramp step  19   a, b  present at the end of the ramp, abutting against it and preventing the reverse rotation. A stop rib  20  is also provided on the ramp surface, against which the ratchet legs  18  abut to prevent any further knob rotation after the knob reaches the position corresponding to the second dose delivery. 
     As shown in  FIGS. 6-8 , a pair of diametrically opposed feet  21  axially extend from the free edge of the dose selection knob  4  over the part  8 b of the plunger rod  8  and engage in respective seats  22  of a support  23  of tubular shape, referred to as cam sleeve  23  ( FIGS. 18 to 20 ) in the present description, formed at the rear end thereof. The seats  22  have a leading edge  22   a  against which the feet  21  abut to bring the cam sleeve  23  into rotation integrally with the dose selection knob  4 . A positioning flange  24  outwardly extends around the same end of the cam sleeve  23  designed to rest on a corresponding rim  25  within the outer body  1  near its rear end, thereby preventing mutual axial sliding. 
     As shown in  FIGS. 18 to 20 , the cam sleeve  23  is formed with two sections with different functions: a first section  23   a  toward the front end, called front section, and a second section  23   b  toward the rear end, called rear section. The front section  23   a  is operatively connected to a slidable sheath  30  (see  FIG. 14 ), whose axial sliding causes the cam sleeve  23  to displace angularly, as will be explained later on, while the rear section  23   b  is operatively connected to the plunger rod  8  through its radial pegs  15  and, as already said, to the dose selection knob  4  (see especially  FIG. 20 ). 
     The cam sleeve  23  is pivotable in the outer body  1  and is kept into axial alignment by the positioning flange  24 . 
     The rear section  23   b  of the cam sleeve  23  is provided with trigger cam means to control the movements of the plunger rod  8 . The trigger cam means comprise two windows  26  diametrically opposed and symmetrical to the axial rotation as regard their shape, opened toward the rear edge of the cam sleeve through a respective axially extending channel  27  defining a first dose trigger cam track  27   a . Each window is delimited by two parallel circumferential sides  26   a ,  26   b , by an axial side  26   c  linking two ends of the sides  26   a ,  26   b , and by an inclined side  26   d , opposed to the axial side  26   c , linking the other end of the side  26   b  opposite to the channel  27  to one side of the channel  27 . The channel  27  opens in the window  26  at the inclined side  26   d  and the axial side  26   c  forms the second dose trigger cam track. The first dose trigger cam track  26   c  is angularly spaced from the second dose trigger cam track  27   a.    
     Drive cam means  28  are embossed on the outer surface of the front section  23   a  of the cam sleeve  23 . The drive cam means  28  is formed by a cam profile repeated four times in an angularly equispaced fashion on said surface. The cam profile comprises a first drive cam track  28   a , extending from the end of the sleeve cam  23 , called upward track for sake of simplicity, and inclined with respect to the axis X, and a second drive cam track  28   b , called downward track for sake of simplicity, extending from the same end of the cam sleeve  23  and incident with the first drive cam track  28   a . On the upward track  28   a  and, successively, on the downward track  28   b  a pair of drive pins  32  is designed to slide. The drive pins  32  project inwardly from two diametrically opposed, axial drive legs  31  of the sliding sheath  30  ( FIGS. 15-17 ). When a pressure action is exerted on the free end  3  of the sliding sheath  30 , the cam sleeve  23  is rotated in the opposite direction to the inclination direction of the upward track  28   a , and, respectively, when the pressure action ceases. 
     In the downward track  28   b  of the drive cam means  28  relevant cantilever legs  29  are formed to be inwardly deflected to allow passage of the drive pins  32 . In the stored state of the device the drive pins  32  abut on an axial lock-out edge  29   a  ( FIGS. 4 and 14 ) at the free end of the cantilever legs  29 , thereby preventing the sliding sheath  30  from moving toward the rear end of the device. A stop edge  28   c , placed sideways of the axial lock-out edge  29   a , serves as abutment for drive pins  32  to prevent the dose selection knob  4  from rotating beyond the positions of first dose and second dose delivery, as will be explained later on. 
     The end of the sliding sheath  30  at the side opposite to the drive legs  31  constitutes the front end  3  of the device, i.e. the end intended to be brought into contact with the patient skin at the injection site. The needle  7   a  of the syringe  7  will project from said front end  3  through a central aperture  33  thereon. A central spring boss  34  for slidably housing the syringe  7  extends from the inner face of the front end  3  of the sliding sheath  30 . A return spring  35  is wound around the central spring boss  34  and abuts against the inner face of the front end  3  with one end and against a surface of the outer body  1  with its other end. 
     The drive legs  31  are slidingly engaged with axial guides  36  formed in the outer body  1 , whereby the sliding sheath  30  may only move axially in the outer body  1 . Two wide axial openings  37 , arranged at 90° relative to drive legs  31 , are formed on sliding sheath  30 . The axial openings  37  are axially aligned to corresponding transparent inspection windows  38  formed on the outer body  1 , through which the barrel  7   c  of the syringe  7  is visible, whereby the user can control the drug delivery condition. The abutment surface for the return spring  35  on the outer body  1  is constituted by the bottom wall  38   a  of said inspection windows  38 . The axial openings  37  allow the sliding sheath  30  to travel axially by the required distance whilst not clashing with the windows in the outer body  1 . 
     A pair of assembly clips  39  extends from the bottom of, and within the axial openings  37  of the sliding sheath  30  to snap engage with corresponding end stops  40  formed at the front end of the outer body  1 , so as to allow the assembly of the sliding sheath  30  within the outer body  1  and prevent release thereof. 
     The front edge of the outer body  1  abuts on respective lead edges  41   a  of a pair of flexible tines  41  formed on the sliding sheath  30  at diametrically opposed sides. The lead edge  41   a  of these tines is inclined so as to provide resistance to the movement of the sliding sheath  30  and make this movement possible only as a result of a moderate thrust that deflects the tines  41  inwardly until the edge of the outer body  1  overcomes the most projecting end of the tines  41 . The motion subsequently created by the release of the tines  41  helps to quickly insert the needle  7   a  of the syringe  7  into the injection site. 
     A tubular housing  42  for the syringe  7  is formed in the outer body  1  and a flange  42   a  is formed at one end thereof, on which a corresponding flange  7   e  of the barrel  7   c  rests. The two flanges are locked to each other by retention clips  43  inwardly projecting from the outer body  1  (see  FIGS. 5 ,  11  and  13 ). 
     As shown in  FIG. 11 , guide means  44  are embossed on the inner surface of the outer body  1  to control the axial movement of the plunger rod  8  and limit in this way the volume of delivered drug. These guide means are in the form of a stepped track with a first location face  44   a , a second location face  44   b  and a stop ledge  44   c , lying on planes perpendicular to the axis X. The edge of the first location face  44   a  is connected to the second location face  44   b  by a first axial side  44   d , and the edge of the second location face  44   b  is connected to the stop ledge  44   c  by a second axial side  44   e . A pair of diametrically opposed stepped tracks, symmetrical to the axial rotation as regards their shape, are formed in the outer body  1 . The radial pegs  15  of the plunger rod  8  are designed to slide along the first and the second location faces  44   a  and  44   b  as a result of the rotation of the cam sleeve  23  and fall off from the first location face  44   a  to the second location face  44   b  and from the latter to the stop ledge  44   c  on delivering the first and the second dose of drug, while moving along the first axial side  44   d  and, respectively, the second axial side  44   e , as will be explained later on. 
     A needle shield remover  45  ( FIGS. 2 to 5 ) is removably secured to the outer body  1  by snap engageable retention fingers  45   a  and is provided with an inner tubular grip  45   b  fit for engaging with the needle shield  7   b , in such a way that, by pulling the needle shield remover  45  before the first dose is administered, the user can remove the needle shield  7   b  and free the needle  7   a  for the injection. 
     The following is a description of the way the auto-injector device according to the invention is used. 
     In the initial state, the stored state, the power spring  10  is compressed between the closed end of the part  8   a  of the plunger rod  8  and the bottom wall  4   a  of the dose selection knob  4 . The bayonet connection between the knob  4  and the plunger rod  8  secures the power spring  10  in compression until the first dose is selected. Any buckling of the power spring  10  is prevented thanks to its being arranged between the radial ribs  9  and the part  8   a  of the plunger rod  8  at one side and the support rod  11  at the other one. The needle shield  7   b  is secured to the syringe  7  and the needle shield remover  45  secured to the needle shield  7   b . The cap  2  is secured to the outer body  1  and the sliding sheath  30  is prevented from moving axially because the drive pins  32  of the of the drive legs  31  abut against the respective lock-out edges  29   a  of the cam sleeve  23 . 
     The dose selection knob  4  is connected to the outer body  1  through its external perimetrical groove  16 , with which slidingly engages the undercut  17  on the rear end of the outer body  1 . Once assembled, the dose selection knob  4  cannot move axially, but can only rotate in one direction. The rotation direction is indicated by the reference marks on the outer body: in other words, indicator  5  starts from the position  1  , rotates to the position  1  when the first dose is selected, and then rotates to the position  2  when the second dose is selected. 
     In the stored state the device is “locked-out”, i.e. the sliding sheath  30  cannot move in the outer body  1 , because the drive legs  31  of the sliding sheath  30  abut against the axial lock-out edges  29   a  of the cam sleeve  23 . This condition is shown in particular in  FIG. 14 . On selecting the first dose (position  1 ), the device is unlocked as shown in  FIG. 21 . As a matter of fact, by rotating the dose selection knob  4  the cam sleeve  23  is pushed in the same direction by the feet  21  of the knob  4  that abut on the leading edge  22   a  of the seats  22  of the cam sleeve  23 . The dose selection knob  4  cannot rotate past the position  1  until the first dose is delivered, because the drive pins  32  of the legs  31  abut on the circumferential stop edge  28   d  of the cam track  28  on the cam sleeve  23 . The slidable sheath  30  is prevented from rotating because the legs  31  can only move axially forward and backward in the axial guides  36  on the outer body  1 . 
     First the user must slide back and remove the end cap  2  in order to expose the needle shield remover  45 . The end cap  2  will have to be replaced once the first dose is delivered when the device is not in use. The end cap  2  protects the drug from light exposure and prevent particulates from coming into contact with the front end  3  of the device. 
     To perform the first injection the user must remove the needle shield remover  45 . In this way the needle shield  7   b  is also removed leaving the needle  7   a  uncovered, but still sub-flush of the front end  3  and not readily visible to the user. To unlock the device and select the delivery of the first dose, the user rotates the dose selection knob  4  from position  0  (stored state) to position  1  (first dose armed). 
     The rotation of the dose selection knob  4  from position  0  to position  1  causes the rotation of the cam sleeve  23 , whereby the axial lock-out edges  29   a  of the cantilever legs  29  displace relative to the drive pins  32  of the legs  31  of the slidable sheath  30 , which abut against the circumferential stop edge  28   d  to prevent the knob  4  to further rotate until the first dose is delivered and are aligned to the upward portions  28   a  of the cam track  28  free to move along them. The user recognizes the end of rotation to position  1  when he/she sees that the indicator  5  lines up with the position  1  marker, feels the increase in rotation resistance of the drive pins  32  contacting the cam track  28  and also hears the “click” as produced by the ratchet legs  18  falling off the step  19   a  of the ramp surface  19 . The contrast between legs  18  and steps  19   a  prevent the knob  4  from rotating in the reverse direction. 
     The device is triggered by the user pressing the front end  3  of the sliding sheath  30  against the injection site by keeping the device through the outer body  1 . The movement of the sliding sheath  30  in the outer body  1  finds a resistance due to the contrast between the flexible tines  41  and the end of the outer body  1 . Due to their flexibility and the inclined contact surface, the flexible tines  41  depress and fully deflect inwardly to allow the passage of the sliding sheath  30  which can slide in the outer body  1  leaving the needle  7   a  to project from its front end  3 , so that the needle can penetrate in the injection site. The motion subsequently created by the release of the flexible tines  41  helps to quickly insertion of the needle  7   a  in the injection site. 
     The axial movement of the sliding sheath  30  in the outer body  1  causes the rotation of the cam sleeve  23  and the latter would frictionally draw into rotation also the dose selection knob  4 . To prevent the knob  4  from rotating during the step of first dose delivery, between the dose selection knob  4  and the outer body  1  temporary stop means are provided that mutually engage when the free ends of the ratchet legs  18  fall off the step  19   a  of the ramp surface  19  of the outer body  1 . In the present embodiment the temporary stop means comprise retention pips  46  of the outer body engaging with corresponding catches  47  of the knob  4 , as shown in  FIGS. 6 ,  11  and  22   c . The rotational force acting on the dose selection knob  4  upon triggering is less than the retention force provided by the pips  46 . However, the rotational force that the user is able to provide is much larger than that of pips. Therefore, the user can overcome the pip force and rotate the knob  4  to arm the device for the second dose. 
     The rotation of the cam sleeve  23  causes the plunger rod  8  to rotate because of the engagement of its radial pegs  15  in the corresponding axial channels  27 . After a few degrees of rotation the bayonet connection between the dose selection knob  4  and the plunger rod  8  decouples because the retention clips  13  of the knob  4  reach the relevant axial release slot branches  12   b  of the plunger rod  8  and, under the action of the power spring  10 , the plunger rod  8  is pushed forward to bring the radial pegs  15  to lean on the first location face  44   a  of the stepped guide  44  of the outer body  1 . 
     While the cam sleeve  23  keeps rotating, the radial pegs, pushed by the first dose trigger cam track  27   a , slide on the first location face  44   a  until they reach the end thereof and fall off the second location face  44   b  of the stepped guide  44  under the action of the power spring  10 . This sequence is shown in  FIGS. 23   a  and  23   b . The resulting axial sliding of the plunger rod  8  causes the delivery of the first dose. 
     After delivery of the first dose, the user removes the device from the injection site and the needle  7   a  withdraws therefrom. The return spring  35  is no longer hindered by the forced contact between the front end  3  and the injection site and thereby pushes the slidable sheath  30  axially forward thus resheathing the needle. At the same time the drive pins  32  of the drive legs  31  slide down in the downward portion  28   b  of the cam track  28  depressing inwardly the cantilever legs  29  until the device returns to a “lock-out” condition, wherein the drive pins  32  contact the free end  29   a  of the cantilever legs  29  and the assembly clips  39  of the sliding sheath  30  again engage with end stops  40  of the outer body  1 , as shown in  FIG. 24 . The needle  7   a  is again not accessible as being covered by the sliding sheath  30 , which, in this state, is prevented from sliding until the user rotates the dose selection knob  4  to position  2 . The user then recaps the device. The end cap  2  snap fits with outer body  1  to securely hold on the device. 
     If the delivery of a second dose is necessary, the user un-caps the device to enable access to the sliding sheath  30 . To unlock the device the user must rotate the dose selection knob  4  from the position  1  (first dose armed position) to the position  2  (second dose armed position). 
     To that end the user must overcome the reaction of the catches  47  of the knob  4  on retention pips  46  of the outer body  1 . The feet  21  of the knob  4  take up the free travel on seat  22  of the cam sleeve  23  until they reach the leading edge  22   a  to rotate the cam sleeve  23  to position  2 , as shown in  FIGS. 25   a  and  25   b . At the same time the rotation of the cam sleeve  30  causes the device to unlock because the drive pins  32  of the drive legs  31  of the sliding sheath  30  line up the upward portion  28   a  of the cam track  28  while contacting the circumferential stop edge  28   d  to prevent a further rotation of the knob  4  once the position  2  is reached. The reverse rotation of the dose selection knob  4  is prevented by the ratchet legs  18  snap abutting on step  19   a  of the ramp surface  19 . The rotation of the cam sleeve  23  also causes the repositioning of the radial pegs  15  from the outlet of the axial channel  27  within the window  26  to the opposite axial side  26   c , while their position on the second location face  44   b  of the stepped guide  44  is unchanged. 
     The device is triggered for the delivery of the second dose by the user pressing the front end  3  of the sliding sheath  30  against the injection site by keeping the device through the outer body  1 . The movement of the sliding sheath  30  in the outer body  1  finds a resistance due to the contrast between the flexible tines  41  and the end of the outer body  1 . Due to their flexibility and the inclined contact surface, the flexible tines  41  depress and fully deflect inwardly to allow the passage of the sliding sheath  30  which can slide in the outer body  1  leaving the needle  7   a  to project from its front end  3 , so that the needle can penetrate in the injection site. The motion subsequently created by the release of the flexible tines  41  helps to quickly insert the needle  7   a  in the injection site. 
     To prevent any further rotation of the knob  4 , once the position  2  is reached, at the end of the following rotation of the cam sleeve  23  the base of the ratchet legs  18  contacts the stop rib  20  of the indexing ramp  19 , by what the ratchet legs  19  are retained between the step  19   a  and said stop rib  20 . 
     While the cam sleeve  23  keeps on rotating, the radial pegs  15  slide on the second location face  44   b  of the stepped guide  44  as pushed by the axial side  26   c  of the window  26  until they reach the end of said face, from which they fall off the stop ledge  44   c  of the stepped guide  44  due to the action of the power spring  10 . This operating sequence is shown in  FIGS. 26   a  and  26   b . The resulting axial sliding of the plunger rod  8  causes the second dose to be delivered. 
     It is worth noting that a small drug volume always remains in the syringe barrel. In fact, the position of the stop ledge  44   c  of the stepped guide  44  is designed in the way that, when the radial pegs  15  reach the stop ledge  44   c , the plunger stopper  7   d  does not touch the bottom of the barrel  7   c . In this way, not only the delivery of the prescribed volume of drug is allowed to be controlled, but also any manufacturing variability with respect to the internal length of the syringe barrel is ensured to be mitigated. Therefore the dose accuracy is improved. 
     After delivery of the second dose, the user removes the device from the injection site and the needle  7   a  withdraws therefrom. The return spring  35  is no longer hindered by the forced contact between the front end  3  and the injection site and thereby pushes the slidable sheath  30  axially forward thus resheathing the needle. At the same time the drive pins  32  of the drive legs  31  slide down in the downward track  28   b  of the drive cam means  28  and depress inwardly the cantilever legs  29  until the device returns to a “lock-out” condition, wherein the drive pins  32  contact the free end  29   a  of the cantilever legs  29  and the assembly clips  39  of the sliding sheath  30  again engage with end stops  40  of the outer body  1 , as at the end of the delivery of the first dose. The needle  7   a  is again not accessible as being covered by the sliding sheath  30 . The user then recaps the device with its end cap  2  before disposal/handling to paramedic. 
     Even if the autoinjector device according to the invention described above is equipped with two radial pegs  15  to guide the movements of the plunger rod  8 , this solution being the preferred one to have a symmetrical distribution of the forces acting on the various components, it is clear that the solution in which only one radial peg  15  is provided is comprised in the scope of the invention as being an obvious variation thereof. In this case, the stepped guide means  44 , the trigger cam means  26 ,  27  and the drive cam means  28  will be modified consequently. 
       FIGS. 27 to 48  show a second embodiment of the autoinjector device according to the invention featured by a different configuration of some components, while maintaining a substantially equal operation relative to the autoinjector device described above. 
     With reference to  FIGS. 27-31 , in the autoinjector device according to the second embodiment of the present invention the outer body, generally indicated at  100 , is formed by two distinct components  100   a  and  100   b , called chassis and outer sleeve respectively, which can be secured to each other coaxially. In particular, a portion of the chassis  100   a  engages within sleeve  100   b  and is secured thereto by teeth  101   a  snap fitting in corresponding grooves  101   b  of sleeve  100   b  (see  FIG. 36 ). The outer diameter of sleeve  100   b  is greater than that of the chassis  100   a , thus forming a step  101   c , against which the end of a removable end cap  102  abuts, said cap  102  concealing the front end  103  of the device. The removable end cap  102  is removably fixed to the chassis  100   a  by cap retention teeth  101   d  snap fitting in corresponding grooves  102   a  formed on end cap  102 . A pen-type clip  100   c  extends along the side wall of sleeve  100   b  to hang the autoinjector device, for example, to a pocket. 
     In the proximity of the other end, the rear end, of the outer body  100  angularly spaced reference marks are formed or labelled, for example the numerals 0, 1, 2, indicating a rest or stored state (0), and two operating states (1, 2) of the device, as will be explained later on. 
     A dose selection knob  104 , from which a reference indicator  105  axially extends, is provided at the rear end of the outer body  100 . The dose selection knob  104  is axially pivotable relative to the outer body  100  to allow the indicator  105  to align to the reference marks formed thereon. 
     In the present embodiment of the invention a substantially cup-shaped ratchet  204  is housed underneath the dose selection knob  104 . The ratchet  204  is made integral to knob  104  through a pair of wings  205  internally extending in the knob at diametrically opposite parts and formed with cuts  206  for snap fitting with side axial retention ribs  204   c  of the ratchet  204  (see  FIGS. 32 and 33 ). 
     A syringe group, generally indicated at  106 , is housed in the outer body  100 . As shown in  FIG. 39  the syringe group comprises a drug preloaded syringe  107 , with needle  107   a , needle shield  107   b  (see also  FIG. 29 ), barrel  107   c  and inner plunger stopper  107   d . In the barrel  107   c  there engages the end of a plunger rod  108 , formed by a tubular element in two parts, front part  108   a  and back part  108   b  of different outer diameter. The front part  108   a  has a cross section that is in a clearance condition with respect to the inner section of the barrel  107   c  so that it can slide therein, and an end configured for engagement with the plunger stopper  107   d  as a result of an axial movement to push it forward on drug delivery. The back part  108   b  of the plunger rod  108  has a larger diametrical size. 
     The inner diameter of the plunger rod  108  is sized to house a power spring  110  axially extending all over its length. As shown in  FIGS. 30 and 31 , the power spring  110  is in a compressed state and abuts against the closed end of the front part  108   a  of the plunger rod  108  with one end and against a bottom wall  204   a  of the ratchet  204  with its other end. The power spring  110  also winds up around a support rod  111  extending from a retention hole  204   b  centrally formed in the bottom wall  204   a  of the ratchet  204  up to the closed end of the front part  108   a  of the plunger rod  108 . The arrangement of the power spring  110  between the support rod  111  and the inner wall of the front part  108   a  of the plunger rod helps to minimize buckling of the power spring  110 . 
     From the bottom wall of the dose selection knob  104  there extend inwardly a pair of diametrically opposed bosses  109  ( FIG. 35 ) configured to engage with corresponding cut-outs  207  formed on the bottom of the ratchet  204 , whereby a rotational torque exerted by the user on the dose selection knob  104  is transferred to the ratchet  204  through the bosses  109  and the cut-outs  207  and from the ratchet  204  to the autoinjector device components connected thereto, as will be explained herebelow. 
     The plunger rod  108  and the ratchet  204  are coupled by a bayonet connection that keeps the power spring in a compressed state until the device is triggered. With reference to  FIGS. 33 to 35 , the bayonet connection comprises a pair of retention feet  112  inwardly projecting from the ratchet  204  at diametrically opposed parts and corresponding actuation slots  113  extending from the plunger rod  108  and hanging on the retention feet  112 . The holding stability is ensured by axial force provided by the compressed power spring  110 , but the connection does not have any circumferential constraints other than that due to the mutual friction between feet  112  and slots  113 . 
     Two radial pegs  115  outwardly project from the rear part  108   b  of the plunger rod  108  at diametrically opposed parts. The two radial pegs  115 , shown in particular in  FIGS. 32-34 , provide a means to guide the movement of the plunger rod  108 , which controls the drug dose delivery, by sliding in trigger cam means, as will be explained later on. 
     The connection between the outer sleeve  100   b  and the knob-ratchet assembly is made (see  FIGS. 30 and 31 ) through an inwardly facing flange  150  of the sleeve  100   b  abutting on a running rim  151  of the ratchet  204 , while the free edge of the knob  104  abuts on the rear edge of the outer sleeve  100   b . In this way the sleeve  100   b  is held captive between the selection knob  104  and the ratchet  204  during the snapping together process. Centering ribs  152  extend from the running rim  151  on the ratchet  204  to provide axial alignment between the ratchet  204  and the sleeve  100   b.    
     The dose selection knob  104  may rotate in only one direction relative to sleeve  100   b  and to this end the connection between the ratchet  204  and the sleeve  100   b  comprises means for preventing the rotation in the direction opposite to that of dose selection after the knob reaches one of the operating positions. These means comprise a pair of flexible ratchet legs  118  (see  FIGS. 35 and 36 ) perimetrically extending from the edge of the ratchet  204 , suited to slidably abut, when the knob  104  is rotated, on respective anti-back-rotation ribs  119 , visible in  FIG. 43   c , of the sleeve  100   b . When the legs  118  slide, first they flex due to the presence of ribs  119  and then, once the ribs have overcome, they trigger abutting against it and preventing the reverse rotation of knob  104 . A stop rib  120  (visible in  FIG. 43   c ) is also provided along the face of the sleeve  100   b  on which the ratchet  204  slides. A corresponding protrusion  120   a  of the ratchet  204  abuts against the stop rib  120  to prevent any further knob forward rotation after the knob reaches the position corresponding to the dose delivery. However, the protrusion  120   a  must deflect, as a result of a moderate force, to overcome the stop rib  120  and allow the passage from an operating position to the other. 
     As shown in  FIGS. 33 and 41   a,b,c , a pair of diametrically opposed feet  121  axially extend from the ratchet  204  over the part  108   b  of the plunger rod  108  and engage in respective grooves  122  of a support  123  of tubular shape, referred to as cam sleeve  123  in the present description, formed at the rear end thereof. The grooves  122  have a leading edge  122   a  against which a turning leg  121   a  of the feet  121  abut to bring the cam sleeve  123  into rotation integrally with the dose selection knob  104  through the ratchet  204 . A positioning flange  124  (see also  FIGS. 30 and 31 ) outwardly extend around the same end of the cam sleeve  123  designed to rest with one face on a corresponding rim  125  within the outer sleeve  100   b  near its rear end, and with the other face on the back edge of the chassis  100   a , thereby preventing the mutual axial sliding. 
     As shown in  FIGS. 41   a ,  41   b  and  41   c , the cam sleeve  123  is formed with two sections with different functions: a first section  123   a  toward the front end of the device, called front section, and a second section  123   b  toward the rear end, called rear section. The front section  123   a  is operatively connected to a slidable sheath  130  (see  FIG. 30 ), whose axial sliding causes the cam sleeve  123  to displace angularly, as will be explained later on, while the rear section  123   b  is operatively connected to the radial pegs  115  of the plunger rod  108  and, as already said, to the dose selection knob  104  (see especially  FIG. 42 ) through the ratchet  204 . 
     The cam sleeve  123  is pivotable in the outer sleeve  100   b  and is kept into axial alignment by the positioning flange  124 . The rotation stop end is made by a pair of side ribs  124   a  on the outer edge of flange  124  abutting on corresponding abutments, not shown, formed in the sleeve  100   b.    
     The rear section  123   b  of the cam sleeve  123  is provided with trigger cam means to control the movements of the plunger rod  108 . The trigger cam means comprise two windows  126  diametrically opposed and symmetrical to the axial rotation as regard their shape, opened toward the rear edge of the cam sleeve through a respective axially extending channel  127  defining a first dose trigger cam track  127   a . Each window  126  is delimited by two parallel circumferential sides  126   a  and  126   b , by an axial side  126   c  linking two ends of the sides  126   a ,  126   b , and by an inclined side  126   d , opposed to the axial side  126   c , linking the other end of the side  126   b , opposite to the channel  127 , to one side of the channel  127 . The channel  127  opens in the window  126  at the inclined side  126   d  and the axial side  126   c  forms the second dose trigger cam track. The first dose trigger cam track  127   a  is angularly spaced from the second dose trigger cam track  126   c . In the present embodiment the side  126   b  is placed at the end of a widened gap in windows  126  to account for clearances and tolerances associated with manufacturing variation of component features. 
     Drive cam means  128  are embossed on the outer surface of the front section  123   a  of the cam sleeve  123 . The drive cam means  128  is formed by a cam profile repeated four times in an angularly equispaced fashion on said surface. The cam profile comprises a first drive cam track  128   a , extending from the end of the cam sleeve  123 , called upward track for sake of simplicity, and inclined with respect to the axis X, and a second drive cam track  128   b , called downward track for sake of simplicity, extending from the same end of the cam sleeve  123  and incident with the first drive cam track  128   a . On the upward track  128   a  and, successively, on the downward track  128   b  a pair of drive pins  132  is designed to slidingly urge. The drive pins  132  project inwardly from two diametrically opposed, axial drive legs  131  of the sliding sheath  130  ( FIGS. 40   a ,  40   b  and  40   c ). Sliding occurs when a pressure action is exerted on the free end  103  of the sliding sheath  130 , whereby the cam sleeve  123  is rotated in the opposite direction to the inclination direction of the upward track  128   a , and, respectively, when the pressure action ceases. 
     In the downward track  128   b  of the drive cam means  128  relevant cantilever legs  129  are formed to be inwardly deflected to allow passage of the drive pins  132  during the drive pin return stroke in the downward track. In the stored state of the device the drive pins  132  abut on an axial lock-out edge  129   a  at the free end of the cantilever legs  129 , thereby preventing the sliding sheath  130  from moving toward the rear end of the device. A stop edge  128   c , placed sideways of the axial lock-out edge  129   a , serves as abutment for drive pins  132  to prevent the ratchet  204  from rotating beyond the positions of first dose and second dose delivery, as will be explained later on. 
     The end of the sliding sheath  130  at the side opposite to the drive legs  131  constitutes the front end  103  of the device, i.e. the end intended to be brought into contact with the patient skin at the injection site. The needle  107   a  of the syringe  107  will project from said front end  103  through a central aperture  133  thereon. A return spring  135  abuts with one end against the inner face of the front end  103  of the sliding sheath  130  and against pushing surface of chassis  100   a  with its other end. Sideways the return spring  135  is guided by alignment ribs  134  formed inside the sheath  130 . 
     A pair of assembly clips  139  extends outwardly from the ends of the legs  131  to snap engage with axial guide slots  147  formed along the chassis  100   a . The legs  131  deflect when the device is being assembled so as to allow the assembly clips  139  to engage in the slots  147  and the axial movement of the sliding sheath  130  while preventing release thereof. 
     Since the drive legs  131  are slidingly engaged with axial guide slots  147  formed in the chassis  100   a , the sliding sheath  130  may only move axially in the outer body  100  along axial alignment tracks  136  inwardly projecting from the inner face of the chassis  100   a . Two wide axial openings  137 , arranged at 90° relative to drive legs  131 , are formed on sliding sheath  130 . The axial openings  137  are axially aligned to corresponding transparent inspection windows  138  formed on the chassis  100   a , through which the barrel  107   c  of the syringe  107  is visible, whereby the user can control the drug delivery condition. The abutment surface for the return spring  135  on the chassis  100   a  is constituted by the bottom wall  138   a  of said inspection windows  138 . The axial openings  137  allow the sliding sheath  130  to travel axially by the required distance whilst not clashing with the windows  138  of the chassis  100   a.    
     Flexible tines  141  project from diametrically opposed parts of the sliding sheath  130  and have an active surface inclined so as to provide resistance to the movement of the sliding sheath  130  when it abuts against corresponding inner protrusions  141   a  at the front end of the axial alignment tracks  136  of the chassis  100   a  (see  FIGS. 30 and 37 ) and make this movement possible only as a result of a moderate thrust that deflects the tines  141  inwardly to overcome the protrusions  141   a . The motion subsequently created by the release of the tines  141  helps to quickly insert the needle  107   a  of the syringe  107  into the injection site. 
     A tubular housing  142  for the syringe  107  is formed in the chassis  100   a  and an inward edge  142   a  is formed at the front end thereof, on which the front end of the barrel  107   c  seats. At the other end of the tubular housing  142  the barrel  107   c  projects with a flange  107   e , above which the front face of the cam sleeve  123  lies (see  FIGS. 30 and 31 ). 
     As shown in  FIG. 37 , guide means  144  for the radial pegs  115  are embossed on the inner surface of the chassis  100   a  to control the axial movement of the plunger rod  108  and limit in this way the volume of drug delivered. These guide means are in the form of a stepped track with a location face  144   a  and a stop ledge  144   c , lying on planes perpendicular to the axis X. The edge of the location face  144   a  is connected to the rear edge of the chassis  100   a  by a first axial side  144   d  and to the stop ledge  144   c  by a second axial side  144   e . A pair of diametrically opposed stepped tracks, symmetrical to the axial rotation as regards their shape, are formed on the inner face of the chassis  100   a . The radial pegs  115  of the plunger rod  108  are designed to jump down from a position at the rear of the chassis  100   a , whereby the relative axial position of the pegs  115  is defined by the connection of the bayonet feature between retention feet  113  and actuation slots  112 , onto the location face  144   a  at the first dose delivery, and to slide on it as a result of the rotation of the cam sleeve  123 , finally falling off from the location face  144   a  to the stop ledge  144   c  on delivering the second dose of drug, while moving along the first axial side  144   d  and, respectively, the second axial side  144   e , as will be explained later on. 
     A needle shield remover  145  is removably secured to the sliding sheath  130  by snap engageable retention fingers  145   a  abutting against a flange at the front end of the sheath  130  and is provided with an inner tubular grip member  145   b  in which an insert  146  is arranged for engaging on the needle shield  107   b  through retention hooks (not shown) digging into the rubber needle shield, in such a way that, by pulling the needle shield remover  145  before the first dose is administered, the user can remove the needle shield  107   b  and free the needle  107   a  for the injection. 
     The operation of the auto-injector device according to the second embodiment of the invention is described here below. As already said, the operation is substantially equal to that of the previously described embodiment of the invention. Reference is made to  FIGS. 42 to 48  hidden line  149 , where present, in these figures indicates the position of the front end of chassis  100   a.    
     In the initial state, the stored state, the power spring  110  is compressed between the closed end of the part  108   a  of the plunger rod  108  and the bottom wall  204   a  of the ratchet  204  integral to the dose selection knob  104 . The bayonet connection between the ratchet  204  and the plunger rod  108  secures the power spring  110  in compression until the first dose is triggered. Any buckling of the power spring  110  is prevented thanks to its being arranged between the part  108   b  of the plunger rod  108  and the support rod  111 . 
     The needle shield  107   b  is secured to the syringe  107  and the needle shield remover  145  is secured to the needle shield  107   b  through the insert  146 . The cap  102  is secured to the chassis  100   a  and the sliding sheath  130  is prevented from moving axially because the drive pins  132  of the drive legs  131  abut against the respective lock-out edges  129   a  of the cam sleeve  123 . 
     The dose selection knob  104  is connected to the outer body  100  as the sleeve  100   b  is held captive between the knob  104  and the ratchet  204  integral to each other. Once assembled, the assembly formed by the dose selection knob  104  and the ratchet  204  cannot move axially, but can only rotate in one direction. The rotation direction is indicated by the reference marks on the outer body  100 : in other words, indicator  105  starts from the position  1  , rotates to the position  1  when the first dose is selected, and then rotates to the position  2  when the second dose is selected. 
     In the stored state the device is “locked-out”, i.e. the sliding sheath  130  cannot move in the outer body  100 , because the drive legs  131  of the sliding sheath  130  abut against the axial lock-out edges  129   a  of the cam sleeve  123 . This condition is shown in particular in  FIGS. 42   e    43   a . On selecting the first dose (position  1 ), the device is unlocked as shown in  43   b . As a matter of fact, by rotating the dose selection knob  104  the cam sleeve  123  is pushed in the same direction by the feet  121  of the ratchet  204  that abut on the leading edge  122   a  of the grooves  122  of the cam sleeve  123  with their turning legs  121   a . The dose selection knob  104  cannot rotate past the position  1  until the first dose is delivered, because the drive pins  132  of the legs  131  abut on the stop edge  128   c  of the cam track  128  on the cam sleeve  123 . The slidable sheath  130  is prevented from rotating because the legs  131  can only move axially forward and backward in the axial guide slots  147  on the chassis  100   a.    
     It must be pointed out that, as shown in  FIG. 43   a , in the rest position there is a design clearance Y between the trigger cam track  127   a  and the respective radial peg  115 . A design clearance Z of lower extent exists between the turning legs  121   a  of the feet  121  of the ratchet  204  and the respective leading edges  122   a  of the grooves  122  of the cam sleeve  123 . When the user rotates the dose selection knob  104 , at the beginning he/she must overcome the resistance opposed by the stop rib  120  of the sleeve  100   b  abutting against the protrusion  120   a  of the ratchet  204  ( FIG. 43   c ). The small rotation necessary to do this, brings the turning legs  121   a  into contact to the leading edges  122   a , while a residual clearance still exists between the trigger cam track  127   a  and the respective radial peg  115 . 
     First the user must slide back and remove the end cap  102  in order to expose the needle shield remover  145 . The end cap  102  will have to be replaced once the first dose is delivered when the device is not in use. The end cap  102  protects the drug from light exposure and prevents particulates from coming into contact with the front end  103  of the device. 
     To perform the first injection the user must remove the needle shield remover  145 . In this way the insert  146  and the needle shield  107   b  are also removed leaving the needle  107   a  uncovered, but still sub-flush of the front end  103  and not readily visible to the user. To unlock the device and select the delivery of the first dose, the user rotates the dose selection knob  104  from position  0  (stored state) to position  1  (first dose armed). 
     The rotation of the dose selection knob  104  from position  0  to position  1  causes the rotation of the cam sleeve  123 , whereby the axial lock-out edges  129   a  of the cantilever legs  129  displace relative to the drive pins  132  of the legs  131  of the slidable sheath  130 , which abut against the stop edge  128   c  to prevent the knob  104  to further rotate until the first dose is delivered and are aligned to the upward portions  128   a  of the cam track  128  free to move along them (see  FIGS. 43   b  and  45 ). The user recognizes the end of rotation to position  1  when he/she sees that the indicator  105  lines up with the position  1  marker, feels the increase in rotation resistance of the drive pins  132  contacting the cam track  128  and also hears the “click” as produced by the ratchet legs  118  clicking as a result of their falling off the relevant ribs  119 . The contrast between the legs  118  and the relevant ribs  119  prevents the reverse rotation of the knob  104 , whereas any forward rotation is hindered by the abutment between the stop rib  120  of the sleeve  100   b  and the protrusion  120   a  of the ratchet  204  ( FIG. 43   c ) 
     The device is triggered by the user pressing the front end  103  of the sliding sheath  130  against the injection site by keeping the device through the outer body  100 . The movement of the sliding sheath  130  in the outer body  100  finds a resistance due to the contrast between the flexible tines  141  of the sliding sheath  130  and the inner protrusions  141   a  of the chassis  100   a . Due to their flexibility and the inclined contact surface, the flexible tines  141  depress and fully deflect inwardly while overcoming the protrusions  141   a  to allow the passage of the sliding sheath  130  which can slide in the chassis  100   a  leaving the needle  107   a  to project from its front end  103 , so that the needle can penetrate in the injection site. The motion subsequently created by the release of the flexible tines  141  helps to quickly insert the needle  107   a  in the injection site  FIG. 44   a ). 
     The axial movement of the sliding sheath  130  in the outer body  100  causes the rotation of the cam sleeve  123  and the latter would frictionally draw into rotation also the ratchet  204  and the dose selection knob  104 . To prevent the knob  104  from rotating during the step of first dose delivery, between the ratchet  204  and the sleeve  100   b  temporary stop means are provided that mutually engage when the free ends of the ratchet legs  118  fall off the ribs  119  of the sleeve  100   b . In the present embodiment the temporary stop means comprise the stop ribs  120  of the sleeve  100   b  abutting on the corresponding protrusions  120   a  of the ratchet  204 , as shown in  FIG. 43   c . The rotational force acting on the ratchet  204  upon triggering is less than the retention force provided by the stop ribs  120 . However, the rotational force that the user is able to provide is much larger than that of stop ribs  120 . Therefore, the user can overcome the rib force and rotate the knob  104  to arm the device for the second dose. 
     The rotation of the cam sleeve  123  causes the plunger rod  108  to rotate because of its radial pegs  115 , engaged in the corresponding axial channels  127  are pushed by the trigger cam track  127   a . The angular displacement of the plunger rod  108  causes the bayonet connection to decouple as the actuation slots  113  of the plunger rod  108  slide on the respective retention feet  112  of the ratchet  204  until the slots  113  get free of the feet  112 . This sequence is shown in  FIG. 49 . At this point the power spring  110 , no longer retained by the bayonet connection, applies its elastic thrust on the plunger rod  108  which moves forward in the cam sleeve  123  until radial pegs  115 , sliding in the axial channels  127 , lean on the location face  144   a  of the stepped guide  144  of the sleeve  100   b  (see  FIG. 47   a ). The resulting axial sliding of the plunger rod  108  causes the delivery of the first dose. 
     After delivery of the first dose, the user removes the device from the injection site and the needle  107   a  withdraws therefrom. The return spring  135  is no longer hindered by the forced contact between the front end  103  and the injection site and thereby pushes the slidable sheath  130  axially forward thus resheathing the needle. At the same time the drive pins  132  of the drive legs  131  slide down in the downward portion  128   b  of the cam track  128  depressing inwardly the cantilever legs  129  until the device returns to a “lock-out” condition, wherein the drive pins  132  contact the free end  129   a  of the cantilever legs  129  and the assembly clips  139  of the sliding sheath  130  again engage with end stops  140   a  in the axial guides  136  of the chassis  100   a , as shown in  FIG. 46   a    
     The needle  107   a  is again not accessible as being covered by the sliding sheath  130 , which, in this state, is prevented from sliding until the user rotates the dose selection knob  104  to position  2 . The user then recaps the device. The end cap  102  snap fits with outer body  100  to securely hold on the chassis  100   a.    
     If the delivery of a second dose is necessary, the user un-caps the device to enable access to the sliding sheath  130 . To unlock the device the user must rotate the dose selection knob  104  from the position  1  (first dose armed position) to the position  2  (second dose armed position) (see  FIGS. 46   a  and  46   b ). 
     To that end the user must overcome the reaction of the stop ribs  120  of the sleeve  100   b  on the protrusions  120   a  of the ratchet  204 . Deflection of protrusions  120   a  allows the knob  104  to rotate. The feet  121  of the ratchet  204  take up the free travel on grooves  122  of the cam sleeve  123  until the turning legs  121   a  reach the leading edges  122   a  to rotate the cam sleeve  123  to position  2 , as shown in  FIGS. 46   a  and  46   b . In this case too, reaching the position  2  is announced by a click as for the position  1 . 
     The rotation of the cam sleeve  123  causes the device to unlock because the drive pins  132  of the drive legs  131  of the sliding sheath  130  line up the upward portion  128   a  of the cam track  128  while contacting the stop edge  128   c  to prevent a further rotation of the knob  104  once the position  2  is reached. The reverse rotation of the dose selection knob  104  is prevented by the ratchet legs  118  snap abutting on the protrusions  119  of the sleeve  100   b . The rotation of the cam sleeve  123  also causes the repositioning of the radial pegs  115  from the outlet of the axial channel  127  within the window  126  to the opposite axial side  126   c , while their position on the location face  144   a  of the stepped guide  144  is unchanged ( FIGS. 46   b  and  47   a ). 
     The device is triggered for the delivery of the second dose by the user pressing the front end  103  of the sliding sheath  130  against the injection site by keeping the device through the outer body  100 . The movement of the sliding sheath  130  in the chassis  100   a  caused by the drive pins  132  of the legs  131  pushing against the upward track  128   a  finds a resistance due to the contrast between the flexible tines  141  of the sliding sheath  130  and the inner protrusions  141   a  of the chassis  100   a . Due to their flexibility and the inclined contact surface, the flexible tines  141  depress and fully deflect inwardly overcoming the protrusions  141   a  to allow the passage of the sliding sheath  130  which can slide in the chassis  100   a  leaving the needle  107   a  to project from the front end  103 , so that the needle can penetrate in the injection site. The motion subsequently created by the release of the flexible tines  141  helps to quickly insert the needle  107   a  into the injection site. The thrust produced by the drive pins  132  does not cause any significant axial movement of the cam sleeve  123 , because its positioning flange  124  axially abuts against the rim  125  of the sleeve  100   b.    
     To prevent any further rotation of the knob  104 , once the position  2  is reached, at the end of the following rotation of the cam sleeve  123  the free end of the ratchet legs  118  abut on the stop ribs  119  thus preventing the reverse rotation of the knob  104 , whereas the forward rotation is hindered by the contrast between the stop rib  120  of the sleeve  100   b  and the protrusion  120   a  of the ratchet  204  ( FIG. 43   c ). 
     While the cam sleeve  123  keeps on rotating, the radial pegs  115  slide on the location face  144   a  of the stepped guide  144  as pushed by the axial side  126   c  of the window  126  until they reach the end of said face, from which they fall off the stop ledge  144   c  of the stepped guide  144  due to the action of the power spring  110 . This operating sequence is shown in  FIGS. 47   a  to  47   c . The resulting axial sliding of the plunger rod  108  causes the second dose to be delivered. 
     After delivery of the second dose, the user removes the device from the injection site and the needle  107   a  withdraws therefrom. The return spring  135  is no longer hindered by the forced contact between the front end  103  and the injection site and thereby pushes the slidable sheath  130  axially forward thus resheathing the needle. At the same time the drive pins  132  of the drive legs  131  slide down in the downward track  128   b  of the drive cam means  128  and depress inwardly the cantilever legs  129  until the device returns to a “lock-out” condition, wherein the drive pins  132  contact the free end  129   a  of the cantilever legs  129  and the assembly clips  139  of the sliding sheath  130  again engage with end stops  140   a  in the axial guides  136  of the chassis  100   a , as at the end of the delivery of the first dose. The needle  107   a  is again not accessible as being covered by the sliding sheath  130 . The user then recaps the device with its end cap  102  before disposal/handling to paramedic. 
     The autoinjector device according to the invention is suitable to the delivery of medicaments in solution, especially epinephrine (also known as adrenaline). 
     In particular, the doses of epinephrine that can be administered with the device of the invention are preferably in the range of 0.05 mg to 0.5 mg for each delivered dose (from 0.1 mg to 1 mg if two doses are considered). 
     Preferred doses for each delivery are 0.05 mg, 0.10 mg, 0.15 mg, 0.30 mg and 0.50 mg. 
     The above doses are based on a concentration of the epinephrine solution preferably ranging from 0.05 mg/ml to 0.5 mg/ml, the concentrations 0.05 mg/ml, 0.1 mg/ml, 0.16 mg/ml, 0.3 mg/ml and 0.5 mg/ml being particularly preferred.