Prefilled ampoule-syringe of unitary dose

A prefilled ampoule-syringe of unitary dose comprises an ampoule being closed at one of its ends, the other end being open. The ampoule further comprises a narrowed zone. A hollow capsule is arranged at top of the opening of the ampoule. This capsule is connected to a movable stopper means comprising a stopper head and a hollow cylindrical member having a radial channel and a peripheral rim. This rim acts as a retention member during the storage and as a piston ring during the injection. In order to avoid the loss of its elasticity, the rim is located within a belt of enlarged diameter downstream from the narrowed zone during the storage.

The present invention concerns a prefilled ampoule-syringe of unitary dose 
comprising an ampoule being open at one of its ends and provided with a 
narrowed zone near said end, stopper means of elastomeric material being 
engaged within the ampoule and axially movable between a storage position 
and a working position, the stopper means comprising an interior conduit 
provided for bringing into communication a needle holding tip and the 
interior of the ampoule when the stopper means is in its working position, 
the interior conduit comprising an axial channel and a radial channel 
connected to the axial channel, the stopper means being integral with a 
capsule arranged above the zone of the open end of the ampoule and 
comprising a stopper head which is prolonged by a flexible hollow 
cylindrical member which covers a central stiffening tip connecting the 
stopper means and the capsule, the hollow cylindrical member comprising 
the radial channel and at least one peripheral rim provided downstream 
from the radial channel. 
The pharmaceutical industries provide through their good fabrication 
practices and serious controls medicaments of very high quality. However 
too often this quality is decreased by bad administration conditions which 
are met in some hospitals or in ambulatory praxis. To eliminate these 
draw-backs and to ensure that theese medicaments to arrive the patients 
with a maximum of security, the unitary dose has been developped, 
particularly for oral liquid or solid forms, for drinkable liquids and for 
eye washings. For injectable medicaments the proposed solutions are still 
far from being satisfactory. 
Injectable medicaments are generally provided in glass ampoules which have 
certains advantages for the manufactory, one of them being the low 
production cost. However their utilization is not free of inconveniences 
due to the fact that the ampoule is not in a form which is ready for its 
use. In this connection volume errors or calculations errors may be 
mentionned, as well as the possibility of incompatible mixtures in the 
same syringe, the contamination by particles or germs during the filling 
of the syringe (which is often reutilized), particular habits of the 
personnel of the hospital during the preparation and the later utilization 
of the medicaments, since in many hospitals the filling of the syringe is 
carried out long before the moment of injection. Finally the 
identification of the syringe is often missing or incorrect. 
To eliminate this difficulties which may lead to serious accidents for 
patients, there is only one solution: the generalization of the unitary 
dose which alone permits the direct administration of an active principle 
without intermediate preparation. 
Till now different types of unitary doses have been proposed in the form of 
self-injectable syringes or prefilled syringes. 
The difficulties met therewith during their fabrication or their use have 
however not permitted their broad commercialisation. 
Moreover the total cost stays a major obstacle to their generalization. 
Finally some of the proposed devices are not completely satisfactory 
because they require the piercing of a membrane or of a stopper by means 
of an expensive double needle, with risks of detaching solids particles of 
the membrane or of the stopper, which particles may enter into the liquid 
medicament and be injected therewith into the patient's tissue. 
The device which resolves all of theese problems and which provides the 
closest prior art with respect to the present invention is described in 
the published european patent application Nr. No. 111 796 of the same 
applicant. 
In this embodiment, the ampoule comprises a narrowed zone of relatively 
great axial dimensions. The stopper means is disposed within this narrowed 
zone during the whole storage time of the syringe. Because of this 
narrowed zone, the stopper means made of elastomeric materiel is strongly 
compressed during a storage time which may extend over several years, so 
that it may undergo a negative deformation, a kind of retentivity able to 
prevent a quick return back movement of said stopper means when the 
syringe is being used. This phenomenon risks to jeopardize the normal 
working of the stopper means and particulary of the peripheral rim 
arranged around the hollow cylindrical member of the stopper means which 
its disposed downstream of the radial channel. Even though the replacement 
of one rim by several annular lips being disposed one under the other, and 
a preliminary selection of the components may permit to overcome the 
mentioned inconveniences, there are much simpler solutions which are the 
subject of the present invention. 
Moreover, in the system relating to the prior art the positioning of the 
stopper means creates a relatively high pression in the interior of the 
ampoule. In order to reduce this pression which is beneficial to be 
maintained on a relatively low level, their are several possibilities: a 
partial vacuum may be provided which is compensated at the moment of the 
positioning of the stopper means, or the stopper means may be introduced 
in compressed condition to let the gas escape, or by providing above the 
medicament to be injected a gas volume which is substantially twice the 
volume of the stopper means. Theese three solutions however are not very 
interesting, the first two of them because of the complexity and the cost 
of the installation, the third one because of the increased volume of the 
syringe. 
Finally there is the problem of fabrication tolerances of the ampoule and 
the stopper means. Since the fabrication tolerances of the ampoule are in 
the order of +/-0.15 mm and those of the stopper means in the order of 
+/-0.10 mm, in certains extreme cases the compression at the level of the 
narrowed zone is excessive and the positioning of the stopper means is 
therefore getting difficult due to a strong friction of the peripheral 
rims which are arranged downstream of the radial channel, resulting in a 
difficult movement of the stopper means which acts like a piston within 
the body of the ampoule. A preliminary selection of the ampoules and the 
stopper means regarding to their cross section, their separation into 
batches of same dimensions, followed by appropriate marking may eventually 
be an acceptable solution to this problem. However, such a solution even 
though realisable may remain expensive. 
The present invention aims to eliminate all these drawbacks of the prior 
art by extremely simple constructive means which avoid the necessity of 
expensive and complex installations. 
Therefore the prefilled ampoule-syringe according to the invention is 
caracterized in that the peripheral rim provided downstream of the radial 
channel is disposed below the narrowed zone of the ampoule when the 
stopper means is in the storage position such that it is bound to only a 
weak compression during the storage. 
According to a first embodiment, the narrowed zone may be adjacent to the 
open end of the ampoule, the peripheral rim being located in this case 
outside the ampoule when the stopper means is in the storage position. 
According to a second embodiment, the narrowed zone may be located behind 
an enlarged belt adjacent to the open end of the ampoule, the peripheral 
rim being disposed in this case in said belt when the stopper means is in 
the storage position. 
In the latter case, the neck of the ampoule is divided into two portions, 
one of which with reduced cross section provides an obturation zone during 
the storage and the other one, which was called enlarged belt, the 
diameter of which being essentially equal to the body of the ampoule 
permits positioning the rim or the rims or the tightness lips provided 
downstream from the opening of the radial channel, during the storage, 
thereby avoiding an excessive compression of the rim and theireby 
eliminating the risk of a permanent deformation. Since the cross section 
of the enlarged belt is essentially equal to that of the body of the 
ampoule, the flexible rim is bound to the same compression during the 
storage as during the injection. Consequently, its elastical 
caracteristics remain intact during the storage, which ensures its quasi 
instantaneous positioning after the increasing compression to which it is 
bound as it passes through the narrowed zone. The time during which this 
compression occurs is thereby substantially reduced and the rim of 
elastomeric material may thereby not suffer any permanent deformation 
which might endanger the efficiency of the system. In practice just as the 
compression occurs the operator keeps the meedle holding tip at top and 
presses against the ampoule. The rim provided beneath the opening of the 
radial channel passes beyond this narrowed zone by a single push during 
the preliminary air escape phase, that is before the needle of the syringe 
is pushed into the patient's tissue. 
Since the effective height of said narrowed zone is reduced, the volume 
reduction of the gas located above the liquid medicament within the 
ampoule corresponds only to a fraction on the volume of the stopper means, 
which resolves the problem of the over-pressure due to the positioning of 
that stopper means, or of the dimensioning of the ampoule, the gas volume 
of which being consequently reduced. 
Advantageously, as no negative deformation occurs according to a loss of 
elasticity of the elastomeric material during the storage, it is not 
necessary any more to compensate this deformation by exaggerating the 
dimensions of the rim or the tightening lips. This rim may therefore be 
fabricated in its exact dimensions and the syringe being stored for a 
month or several years has pratically no influence on the reaction speed 
of the rim or of the lips when the stopper means is brought into working 
position. Therefore a preliminary selection is no more necessary; thus the 
handling costs and consequently the manufacturing costs of these syringes 
may be reduced. 
Another advantage of this conception results from the rim being a 
protrusion located beneath the opening of the radial channel and being 
situated during the storage beneath the narrowed zone, it constitutes 
thereby a retention means inhibiting the accidental compression of the 
stopper means which acts as a piston within the ampoule. This security is 
added to the very low over-pressure produced within the ampoule by the 
positioning of the stopper means, so that the piston has a tendency to be 
pushed out of the ampoule. To be pushed towards inside the body of the 
ampoule, the piston has to be deliberately pressed therein and preferably 
a small rotation of the ampoule with respect to the capsule may be carried 
out to facilitate the passing of the rim through the narrowed zone. As 
soon as this zone is passed, the compression of the rim within the ampoule 
is extremely weak and thus ensures a maximum flexibility during injection. 
This compression may however be calculated at its minimum since there is 
no danger of permanent deformation as explained above. 
Moreover, since the radial channel is provided within a particularly soft 
elastomeric material, this channel get a reduced diameter or will be 
completely obstructed due to the compression of the stopper means when the 
pressure is too high. This phenomenon, which is in fact not an 
inconvenience, provides a self-regulation of the flow rate of the liquid 
medicament during the injection. By this conception the system imposes an 
essentially constant speed of injection and excludes an injection by fits 
and starts or a too rapid one. 
The height of the stopper head of the stopper means may be lower or higher 
than the height of the narrowed zone of the ampoule. Thereby the 
manufacturing tolerances are not critical and the tightness of the syringe 
during the storage is assured in whatever position the head of the stopper 
means may be in respect to the surface of that narrowed zone, however 
under the condition that the opening of the radial channel be either at 
the level of that narrowed zone or beneath that zone. 
According to a prefered embodiment of the invention, the diameter of the 
stopper head of the stopper means is greater than or equal to the diameter 
of the narrowed zone of the ampoule, but smaller than the inner diameter 
of the body of the ampoule, thereby ensuring the tightness of the ampoule 
when the stopper means is in the storage position and providing an annular 
space between the peripheral surface of said stopper head and the interior 
surface of the body of the ampoule when the stopper means is in its 
working position. 
Since the stopper head must ensure a perfect tightness of the ampoule 
during the storage, its peripheral wall must be strongly pressed against 
the inner surface of the narrowed zone during the storage. To allow the 
medicament to flow during the injection, it is necessary that the stopper 
head has a diameter which is smaller than the inner diameter of the body 
of the ampoule. 
To facilitate the passing of the annular rim through the narrowed zone, the 
enlarged belt adjacent to the open end of the ampoule has advantageously 
at least over a part of its height a conical surface the diameter of which 
varies from the value of the maximum inner diameter of said belt 
progressively to the diameter of the narrowed zone. 
The outer surface of the ampoule adjacent to its open end comprises 
advantageously a protruding edge forming engagement means provided to 
cooperate with complementary engagement means integral with the capsule, 
wherein the capsule stopper means and the stiffening tip are preferably 
designed so that when said engagement means are engaged into each other 
the stopper head is compressed and abuts on the surface of the narrowed 
zone and the peripheral rim is slack or only under low compression within 
the enlarged belt of the ampoule. The precise positioning of those outer 
engagement means ensures a precise positioning of the inner members. 
To ensure a sufficient flexibility of the stopper means, the stopper head 
and the hollow cylindrical member have preferably the shape of a hollow 
cup made of a soft elastomeric material, the walls of which have a cross 
section such that the length of the radial channel may not be greater than 
5 mm. 
The stiffening tip comprising an axial channel has preferably at its upper 
end an annular recess and a sectorial notch provided to bring its axial 
channel into communication with that annular recess. These constructive 
details allow a specially easy manufactoring of the stiffening tip whereas 
a sufficient communication between the radial channel and the axial 
channel of the stopper means are guaranteed.

Refering to FIG. 1, the unitary dose syringe, which is shown in its storage 
position, comprises an ampoule 1 closed at one of its ends and provided 
with an opening 2 at its other end, further comprising a zone 3 of 
narrowed cross section with respect to its body, said zone being located 
adjacent to the open end 2. A hollow capsule 4 is arranged above the 
ampoule 1 and its open end 2. This capsule comprises a head 5, having 
preferably a continuous cylindrical sidewall, which may otherwise be only 
sectorial, and a bottom 6 which its connected to a central tubular member 
7. A needle holding tip 8, which is also connected to the bottom 6 of the 
capsule 4, is aligned with the central tubular member 7 the upper end of 
which forms a stiffening tip 9 which carries the stopper means 10. This 
stopper means 10, as described in more details below, comprises two 
different functions. The first function is carried out during storage of 
the syringe and consists in providing the tightness of the ampoule 
containing a liquid medicament 12 and a gas pocket 13 which is arranged 
above the liquid, in the position of the syringe as shown in FIG. 1. The 
second function is carried out during the use of the syringe and consists 
in serving as a piston for pressing the medicament out through an axial 
channel 14 provided within the central tubular member 7 and the needle 
holding tip 8, in direction to a needle (not shown) which may be coupled 
to this tip by whatever means. 
The stopper means 10 made of a flexible elastomerical material comprises an 
upper portion in the form of a stopper head 15 of substantially 
cylindrical shape and a hollow cylindrical member 16. This assembly is 
connected with the stiffening tip 9 on which the hollow cylindrical member 
16 is fastened by means of retainers 17. The hollow cylindrical member 16 
is provided with a peripheral rim 18, arranged next to its lower free end. 
A radial channel 19 is disposed across the hollow cylindrical member 16. 
This radial channel communicates with the axial channel 14 through an 
annular recess 20 and a sectorial notch 21 located in the upper end of the 
stiffening tip 9. 
The two functions of the stopper means 10 are carried out respectively by 
the stopper head 15, the diameter of which is equal to or greater than the 
inner diameter of the narrowed zone 3 of the ampoule 1 to assure a perfect 
tightness of this ampoule during the storage of the liquid medicament 12, 
and by the peripheral rim 18 which serves as a piston ring during the 
injection phase, thus forcing the liquid medicament to penetrate into the 
radial channel 19 without escaping through the opening of the ampoule. The 
respective positions and their status for each phase of use of the syringe 
will be described in more details with reference to the following figures. 
The capsule 4 is advantageouslyly equipped with a pair of wings 22 for 
easier manipulation of the syringe during the phase of injection. The open 
end 2 of the ampoule 1 preferably comprises a protruding edge 23 provided 
to cooperate with a projection 24 integral with the interior lateral 
surface of the head 5 of the capsule 4. These elements constitute 
retaining means by which an accidental ejection of the stopper means out 
of the ampoule due to the slight over-pressure in its interior may be 
avoided. A label formed for example by a banderole sticking simultaneously 
to the outer wall of the ampoule and to the edge 26 of the sidewall of the 
capsule 4 above the wings 22 guarantees the invulnerability of the syringe 
before its final utilization. 
The embodiment illustrated in FIG. 1 shows an ampoule 1 in which the 
narrowed zone 3 is not directly adjacent to the open end 2, but it is 
separated from the latter by an enlarged belt 27 in which the peripheral 
rim 18 is embedded during the storage phase illustrated in that figure. 
FIG. 2 illustrates the beginning of the positioning of the stopper means 10 
and the capsule 4 coupled with said stopper means. The stopper head 15 has 
a diameter d equal to or preferably slightly higher than the inner 
diameter d' of the narrowed zone 3 of the ampoule. In the prefered 
embodiment shown in this figure the side edge 30 abuts against the upper 
end of a conical zone 31 of the ampoule, which forms the junction between 
the narrowed zone 3 and the enlarged belt 27 of the ampoule 1. At this 
stage the stopper head 15 is pratically subject to no compression other 
than just a small contracting force on the level of its side edge 30. 
The diameter l of the peripheral rim 18 is at least equal to or preferably 
slightly higher than the diameter l' of the interior of the body of the 
ampoule 1. Actually, as mentioned above, the rim 18 serves as a piston 
ring when the stopper means is put in its working position, the piston 
ring thereby ensuring the tightness against the wall of the ampoule for 
preventing leakage of the liquid medicament through the opening of the 
ampoule. The enlarged belt 27 has preferably a diameter l" equal to the 
diameter l' of the body of the ampoule. In this way the peripheral rim 18 
is bound to a small compression during the storage phase, namely the same 
compression as the one to which it will be bound during the injection, so 
that all above mentioned problems of permanent deformation which may be 
provoqued by excessive compression of the rim during the storage phase are 
avoided. In order to completely eliminate this risk it would be sufficient 
providing a diameter l" of the belt 27 which is higher than the diameter l 
of the rim 18. 
Upon continuing to thrust the capsule and the stopper means in the 
direction of the arrow A, a position as illustrated in the FIG. 3 is 
obtained. In this position the stopper head 15, whose height is in this 
case slightly smaller than the height of the narrowed zone 3 of the 
ampoule 1 such that pratically all risks of erroneous positioning due to 
accumulations of fabrication tolerances is eliminated, is completely 
engaged in this narrowed zone, whereby it is slightly if not strongly 
compressed in the interior of this zone. A strong compression does not 
prejudice the proper functioning of the system since the only function of 
this stopper is to assure the tightness of the ampoule during the storage 
phase. Consequently, if after a particulary long storage this stopper has 
lost more or less its elasticity and cannot immediately return to its 
slack state when the stopper means penetrate into the body of the ampoule, 
this does not constitute an inconvenience since the wall of the piston 
ring is maintained by the peripheral rim 18, for which precautions 
avoiding the phenomenoun of permanent deformation were taken. The position 
as illustrated in this figure corresponds to the storage of the syringe. 
The peripheral rim is located in the belt 27 of enlarged cross section or 
eventually in the largest portion of the conical zone 31 which forms the 
junction between the narrowed zone 3 and the belt 27 of enlarged cross 
section. The protruding exterior edge 23 of the ampoule is abutting 
against the projection 24 disposed at the interior of the sidewall of the 
capsule 4. Since the stopper means 10 is integral with the capsule 4, the 
precise positioning of the projecting elements 23 and 24 determines 
precisely the position of the stopper means 10 within the ampoule during 
the storage phase by means of the central tubular member 7 and the 
stiffening tip 9. 
Upon passing from its position as in FIG. 2 to the position of FIG. 3, the 
stopper means creates in the interior of the ampoule a slight overpressure 
due to the decrease of the volume within said ampoule. This decrease of 
the volume is equal to the product of the cross section of the ampoule in 
the narrowed zone into the stroke of the stopper means between both 
positions. If this pressure, which represents certain advantages as far as 
the protection of the medicament contained in the ampoule against 
accidentially contamination is concerned, should be reduced, one could 
effect a filling with the partial vacuum such that the increase of 
pressure be partially set off by the partial vacuum provided during the 
filling operation. 
FIG. 4 illustrates the preparatory phase of the syringe before the 
injection. During this phase the operator pushes against the ampoule in 
the direction of arrow B, whereby care has to be taken for directing the 
syringe upwards so that the gas which was initially contained in the 
ampoule may escape. This phase consists of passing the peripheral rim 18 
over the narrowed zone 3, thus binding the rim to a relatively high 
compression force but of short duration. The stopper head 15 has now 
passed behind the narrowed zone 3 and may expand freely. Its diameter d is 
smaller than the diameter l' of the body of the ampoule 1 such that an 
annular space 40 is provided between the side portion of the stopper head 
the inner wall of the body of the ampoule and allows the liquid medicament 
to flow towards the radial channel 19. 
The passing of the peripheral rim 18 from the position illustrated in FIG. 
3 to the one illustrated in FIG. 4 constitutes an intermediary step 
between a first position, in which the annular rim 18 acts as an 
essentially passive retention means which avoids an accidental movement of 
the ampoule in the direction of arrow B in respect to the capsule, and a 
second position in which it plays an active part as a piston ring as 
further illustrated in FIG. 5. 
FIG. 5 illustrates the syringe in its working position. The movement of the 
ampoule 1 in the direction of arrow C in respect to the capsule 4 and to 
the stopper means 10 connected to said capsule achieves the evacuation of 
the liquid medicament in the direction of arrow F through the radial 
channel 19, the sectional groove 21 arranged in the stiffening tip 9 and 
the axial channel 14 of the central tubular element 7. The annular rim 18, 
upon rubbing against the inner wall of the body of the ampoule, plays the 
role of a piston ring and forces the liquid to follow the described way. 
Since the rim 18, which may however be replaced by a plurality of parallel 
lips, is disposed immediately under the outer opening of the radial 
channel 19, the dead volume that is the quantity of medicament remaining 
in the syringe after the injection may be reduce to a minimun. 
FIG. 6 illustrates a modified form in which the height of a cylindrical 
surface 60 extending laterally around the stopper head 15 and around the 
upper portion of the hollow cylindrical member 16 is greater than the 
height of the narrowed zone 3 of the ampoule. This solution may be of 
interest in order to avoid that the positioning of the stopper means with 
respect to the narrowed zone 3 may be carried out with problems with 
respect to tolerance. 
The embodiment illustrated in FIG. 7 differs from the preceding embodiments 
in that the narrowed zone 3 is adjacent to the open end of the ampoule. In 
this case the peripheral rim 18 may be located outside the ampoule during 
the storage phase, whereby it may not be bound to any compressive force 
during that phase, while maintaining its role of retention means for 
avoiding an accidental penetration of the stopper means into the ampoule. 
The concrete embodiment illustrated in this figure shows the separation of 
the functions of the stopper means and of the annular peripheral rim. With 
respect to an ampoule the body of which has an inner diameter of 10.00 mm, 
the inner diameter of the narrowed zone should be 9.00 mm, the diameter of 
the stopper head should be between 9.20 and 9.80 mm, and the diameter of 
the rim may be for example 10.25 mm. 
During the injection phase, the stopper head is within the body of the 
ampoule. The mean width between the inner surface of the ampoule and the 
peripheral surface of the stopper head may be between 0.10 and 0.40 mm. 
With respect to the first of these values the outflow of the medicament 
occurs normally and the dead volume, that is the quantity of the 
medicament which will be left in the ampoule after the injection is very 
small. For the second value the outflow of the medicament is very good but 
the dead volume is larger. 
During the storage the stopper head is within the narrowed zone. The 
difference of the diameters of the narrowed zone and of the stopper head 
may be between 0.20 and 0.80 mm. This difference must be absorbed by the 
compression of the stopper head. The stronger the compression is, the 
better is the tightness of the ampoule during the storage but the greater 
is the resistance against the detachment at the beginning of the 
utilization of the syringe. 
According to above the dimensions of the narrowed zone and of the rim, the 
compression of said rim, that is the reduction of its diameter at the 
moment the stopper head passes from its storage position to its working 
position, is approximately 1.25 mm. In practice it was established that a 
reduction of 1.75 mm due for instance to an underdementioned diameter of 
the narrowed zone, may cause a jamming of the system. 
A contraction of 0.25 mm of this rim, when the rim is within the ampoule 
and acts as a piston ring, is sufficient to avoid parasitic outflow of the 
medicament towards the opening of the ampoule. 
In practice, the diameter of the stopper head must be at least 0.10 mm. 
smaller than the inner diameter of the body of the ampoule and 0.10 mm 
greater than the diameter of the narrowed zone. The diameter of the 
peripheral rim must be at least 0.10 mm greater than the inner diameter of 
the body of the ampoule. 
A solution to avoid possible problems of bad functioning may consist in 
eliminating the tolerance by appropriate selection of the components. In 
this case the diameter of the body of the ampoule may be fixed at 10.00 
mm, the one of the stopper head at 9.90 mm, the one of the narrowed zone 
of the ampoule at 9.80 mm and the one of the rim at 10.10 mm. The 
compression of the stopper head during storage is 0.10 mm, that of the rim 
during operation equally 0.10 mm. and the mean width of the annular space 
permitting the outflow of the liquid is 0.05 mm. 
Taking into account the tolerances, the inner diameter of the body of the 
ampoule is 10+/-0.50 mm, the one of the stopper head 9.65+/-0.10 mm, the 
one of the narrowed zone of the ampoule 9.35+/-0.10 mm and the one of the 
rim is 10.35+/-0.10 mm. 
The compression of the stopper head during the storage, the compression of 
the rim during operation and the mean width of the annular space are 
comprised respectively between 0.1 and 0.5 mm, 0.1 and 0.6 mm, and 0.05 
and 0.30 mm. 
Another remarkable advantage of the syringes described thereinbefore is the 
presence of a slight over-pressure in the ampoule. In practice, with the 
dimensions as described above, the level of the liquid is proposed to be 
maintained approximatively 5 mm under the stopper means during the 
storage. A greater distance would eliminate the advantage of the 
over-pressure and increase the size of the device. The overpressure depend 
on the reduction of the compressed volume during the positioning of the 
stopper. The movement of the stopper means depend on the height of the 
narrowed zone and on the initial position of the radial channel. The 
reduction of the volume is proportional to the stroke of the stopper means 
between its storage position and the beginning of the working position. In 
theory, the height of gas may be determined such that the gas has attained 
its limit for compression at the end of the stroke of the stopper means. 
However this would cause the jamming of the system by deformation of the 
stopper means. 
The height of the gas above the medicament during the storage is determined 
such that the operator may easily put the stopper means in an intermediate 
position between the storage position and the working position, in which 
the radial channel opens into the body of the ampoule, in which the rim is 
situated such that its function as piston ring is ensured and in which the 
medicament surrounds the stopper head and the opening of the radial 
channel. 
This is an ideal position because it allows a correct positioning of the 
annular rim after its passing through the narrowed zone. 
If the height of gas is insufficient, the liquid risks touching the annular 
rim before the latter is correctly situated. To avoid the risks of 
leakage, the rim may be reinforced or provided in double for instance in 
the form of two superposed annular strips. 
In practice, the height of gas is provided with 8.00 mm before the stopper 
means is put in place. This positioning creates a height reduction of 3.00 
mm. During storage the height of gas is 5 mm and the pressure is in the 
order of 1.6 bar. In order to bring the stopper means into a position in 
which the gas may escape, the necessary movement of the stopper is in the 
order of 2 mm, such that the pressure of the gas immediately before 
escaping from the syringe attains 2.6 bar. A final movement in the order 
of 1 mm brings the liquid into the ideal position as mentioned above. 
The above values are given as examples and not as limitations, while the 
described syringe may undergo various modifications which are obvious to 
the man skilled in the art, without leaving the scope of the present 
invention.