A piston for a syringe and a prefilled syringe using the same

This invention relates to a sealing stopper or piston for a syringe provided with a backstop function and to a prefilled syringe using the same.

As a method of feeding an injection agent as one agent form of a medicament to a medical scene, there is such a system of the so-called prefilled syringe that the injection agent is previously prepared (charged) in a syringe-cum-container, transported and storaged while the end parts thereof are sealed by the piston, the front end of an injection barrel is fitted with an injection needle or administration device during administration, and the piston is forcedly thrusted in the front end and slidably moved in the injection barrel to cause the injection agent to flow out of the injection needle side, as referred to JP-B2-3387775. This method has lately been applied to various uses, because of many advantages that (1) operation is very simple, (2) administration can be accomplished with a correct administration quantity and without misuse of a medicament agent even in an emergency and (3) there is no necessity of transferring a liquid medicament, resulting in easy avoidance of contamination with microorganisms as well as obtaining high sanitary property. The prefilled syringe is of a disposal type such that the prefilled syringe, once used, should be abandoned from a sanitary problem such as infectious disease.

Since the above described syringe, once used, is ordinarily abandoned, under usable state if refilled with a liquid medicament, however, there is such a possibility that the abandoned syringe can be reused for a criminal act such as injection of stimulants and is misused again in a medical scene. In order to completely prevent from these dangers, it is desired to provide such a mechanism that the once used syringe is no longer used again.

As a syringe provided with such a mechanism, for example, there is a structure in which a plunger threaded with a piston has a reuse-preventive projection which is to be engaged with a recess of an injection barrel when the plunger is pushed, so that the plunger cannot be withdrawn (called backstop) , as shown in WO 01/64266 A1. However, the mechanism of this syringe is so complicated that its production cost is considerably increased.

It is an object of the present invention to provide a prefilled syringe provided with a backstop function without increasing the production cost thereof, whereby the disadvantages of the prior art can be overcome.

It is another object of the present invention to provide a sealing stopper or a piston for a syringe, having a reuse preventive backstop mechanism, in economical manner.

These objects can be achieved by a piston for a syringe for sealing an injection barrel filled with a medicament, comprising a skirt part capable of serving as a backstop device.

The accompanying drawings are to illustrate the principle and merits of the present invention in detail. <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a cross-sectional view of one embodiment of a piston for a syringe and a prefilled syringe using the same according to the present invention, (a) a piston or sealing stopper, (b) a injection barrel and (c) a prefilled syringe.</li><li>Fig. 2 is a cross-sectional view of another embodiment of a piston for a syringe, in part, according to the present invention, illustrating dimensions of each part.</li><li>Fig. 3 is a cross-sectional view of a further embodiment of a piston for a syringe, in part, according to the present invention, respectively differing in shape of skirt part of pistons (a) and (b).</li><li>Fig. 4 is a cross-sectional view of a still further embodiment of a piston for a syringe according to the present invention, respectively differing in shape in cross-section (a), (b) and (c).</li></ul>

We, the inventors have made various efforts to impart a reuse-preventive mechanism to a prefilled syringe and consequently, have found that the reuse-preventive device can ecconomically be given to the syringe by composing a stopper for a prefilled syringe to have a backstop function. The present invention is based on this finding. That is, the present invention has the following constructive features: <ul id="ul0002" list-style="none" compact="compact"><li>(1) A piston for a syringe for sealing an injection barrel filled with a medicament comprising a skirt part capable of serving as a backstop device.</li><li>(2) The piston for a syringe as described in (1) , wherein the piston is subjected to film lamination and/or lubricant coating, the skirt part has a rubber exposed surface on a contact surface with the injection barrel and at least a part of the rubber exposed surface is inside the maximum outer diameter of the stopper and outside the inner diameter of the injection barrel.</li><li>(3) The piston for a syringe as described in (1) or (2), wherein an angle of the skirt part is in a range of 30 to 80° based on a standard surface vertical to such a direction that the piston is slidably moved in the injection barrel.</li><li>(4) A prefilled syringe comprising an injection barrel filled with a medicament and sealed by a piston, the piston is the piston for a syringe as described in any one of (1) to (3).</li></ul>

Fig. 1 is a schematic cross-sectional view of one embodiment of a piston for a syringe (which will hereinafter be referred to as "piston") and a prefilled syringe using the same according to the present invention, the piston 1 shown as (a) in Fig. 1 comprises a rubber-made piston body 2, the surface of which is laminated with a resin film 3. A plunger rod 4 (not shown) is fitted to the piston at a fitted position. In a preparation step for an injection medicament, the end of an injection barrel 7 is sealed by a cap 8 as shown in Fig. 1, (c), after which an injection medicament 9 is filled and prepared in an injection barrel 7 shown in Fig. 1 (b) and sealed by the piston 1 to give the prefilled syringe. Ordinarily, a needle part, plunger part and cover parts for each part (all not shown) are added thereto to prepare a finished article.

In Fig. 2, there is shown another embodiment of a piston for a syringe according to the present invention, as enlarged in part and as a front view in part, in which the same remarks as those in Fig. 1 have the same meaning.

The piston 1 has a skirt part 5 having a backstop function. The piston 1 is usually subjected to film 3 lamination and/or lubricant coating on the surface thereof and it is desirable to allow a contact surface of the skirt part 5 with the inner wall of the injection barrel 7 to provide with the rubber exposed surface 6, since a friction resistance is increased when a drawing force is applied to the piston 1.

Moreover, it is desirable that at least a part of the above described rubber exposed surface 6 is inside the maximum outer diameter of the piston and outside the inner diameter of the injection barrel. In order to ensure the sealing property, the maximum outer diameter b of the piston 1 is ordinarily enlarged to be larger than the inner diameter c of the inj ection barrel 7, and the position of the rubber exposed surface 6 is so controlled as to impart such a degree that the rubber exposed surface 6 is not so strongly contacted with the injection barrel 7 that the resistance during compressing is not so excessive and a backstop action can be given when a drawing force is applied.

When the central axis of the piston 1 and that of the skirt part 5 become complete, for example, it is preferable that the maximum diameter a of the rubber exposed surface 6 is smaller than the maximum outer diameter b of the piston 1 and is larger than the inner diameter c of the injection barrel 7 (c&lt;a&lt;b) . When the central axis of the piston 1 and that of the skirt part 5 are shifted, the object of the present invention can be achieved if at least a part of the rubber exposed surface 6 is contacted with the inner surface of the injection barrel 7 and a diameter a' when the skirt part 5 is wound is larger than the inner diameter c (a'&gt;c), even if a&lt;c regarding the above described a and c. Such a structure is most preferable that when the piston 1 is compressed (advanced) in the injection barrel 7, only a part of the rubber exposed surface 6 is contacted with the inner surface of the injection barrel 7, and when it is drawn (backed), the whole circumference-of the skirt part 5 is contacted with the inner surface of the injection barrel 7 to cause a backstop action. This is due to that when the piston 1 is advanced, the slidable resistance is suppressed to a minimum limit and when it is backed, a sufficient resistance enough to backstop the piston 1 can be obtained.

Furthermore, the skirt part 5 has preferably an angle (α in Fig. 2) of the skirt part in a range of preferably 30 to 80° , more preferably 40 to 70° based on a standard surface vertical to such a direction that the piston for a syringe is slidably moved in the injection barrel. When the angle α is at least 30° , the width of the skirt part 5 can sufficiently be maintained, a friction resistance sufficient enough to backstop the piston 1 can be obtained and the slidable resistance is not enlarged to be more than the required value when the piston 1 is advanced in the injection barrel 7. When it is adjusted to at most 80° , on the other hand, the skirt part 5 can well be turned up when the piston 1 is backed away.

The skirt part 5 of the piston 1 shown in Fig. 2 is over the whole circumference of the stopper, but it is not always provided over the whole circumference, but can intermittently be provided.

In addition, the position of the skirt part 5 is not particularly limited, but it is preferable to arrange the skirt part at the end of the plunger side as shown in Fig. 2 from the standpoint of ease of the production.

Fig. 3(a) and (b) are cross-sectional views of other embodiments of the piston 1 according to the present invention, where the piston 1 has the skirt part 5 in the form of other shapes, and Fig. 4(a) to (c) are cross-sectional views of further embodiments of the piston 1 according to the present invention in the form of further shapes, in which the same remarks as those in Fig. 1 and Fig. 2 have the same meanings.

In Fig. 1 to Fig. 4, a case of laminating a rubber-made piston body 2 with a resin film 3 is exemplified, and the laminated resin film 3 is not limited thereto but any material capable of obtaining a required kinematic friction coefficient (e.g. a kinematic friction coefficient of at most 0.2 measured according to JIS K 7218-1986) when fitted to a plunger and pushed into an injection barrel 7 can be used. Accordingly, other known means such as coating of lubricants can be selected for this purpose.

For the resin film 3 can be used fluoro resins such as tetrafluoro ethylene resin (PTFE), tetrafluoroethylene-perfluoroethylene copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), trichlorotrifluoroethylene (PCTFE), poly-vinylidene fluoride (PVDF), polyvinyl fluoride (PVF), etc. and further, can also be used ultra-high molecular weight polyethylene, etc. in addition to the fluoro resins.

Lamination of a rubber-made piston body 2 with a resin film 3 can be carried out by a known prior art technique, for example, a method comprising optionally subjecting one surface of a film to a chemical treatment (chemical etching), sputter etching or corona discharge, arranging it in a shaping mold with a rubber compound to be a basic material for the piston body 1, and then vulcanizing or bonding to form into a pre-determined shape. Of course, a site to be laminated includes a part that can be contacted with the inner wall of the injection barrel 7 or with a medicament, etc., without intending to be limited thereto, in addition to at least a part (rubber exposed surface 6) of the contacted surface of the skirt part 5 with the inner wall of the injection barrel 7.

As a lubricant, there can for example be used silicone oils, fluorinated oils, etc. Useful examples of the fluorinated oil are Demnum (commercial name of Daikin Industries, Ltd.), Krytox (commercial name of Du Pont Kabushiki Kaisha) , etc. A site to be coated with the lubricant includes a part that can be contacted with the inner wall of the injection barrel 7, etc. without intending to be limited thereto, in addition to at least a part (rubber exposed surface 6) of the contacted surface of the skirt part 5 with the inner wall of the injection barrel 7.

In order to maintain at least a part of the contacted surface of the skirt part 5 with the injection barrel 7 to be the rubber exposed surface 6, for example, there can be employed a method comprising molding a rubber in the form of a sheet consisting of a number of rubber-made piston bodies 2 bonded at the skirt part 5, subjecting the resulting sheet to laminate working or lubricant coating in the form of the sheet and then separating the contacted surface of the skirt part 5 with the injection barrel 7.

A rubber for the material of the rubber-made piston body 2 of the piston is not particularly limited, but can for example be selected from synthetic rubbers or natural rubbers such as butyl rubbers, chlorinated butyl rubbers, isobutylene-isoprene-divinylbenzene-ternary polymerization partially cross-linked butyl rubbers, acrylnitrile-butadiene-rubbers, isoprene rubbers, butadiene rubbers, styrene-butadiene rubbers, ethylene-propyrene rubbers, isoprene-isobutylene rubbers, nitrile rubbers, etc., as a predominant component, to be compounded with fillers, cross-linking agents or the like.

As a thermoplastic elastomer, there can also be used solution polymerization type styrene-butadiene rubbers (SBS block copolymer), polyester or polyether urethane rubbers, polyether aromatic polyester block copolymers (polyester rubbers), polyolefin block copolymers, high trans-1,4-polyisoprenes, polyethylenebutyl graft copolymers, syndiotactic polybutadiens and the like.

In addition to the foregoing, relatively soft plastics, for example, plastics of copolymer type and having substantially the same heat resistance (preferably about 130 to 140 °C) as poly-propylene, such as polypropylenes of copolymer type, low density polyethylenes, ethylene-vinyl acetate copolymers, etc. can also be used.

Moreover, the hardness of the piston of the present invention is not particularly limited, but is suitably selected depending on the shape or the like of the piston and from the standpoint of maintaining the sealing property of a prefilled syringe and compressing the piston with a suitable force as well as effectively exhibiting the backstop function, the hardness is preferably measured by a method defined by JIS K 6253 A, which is preferably within a range of 50 to 65, more preferably 55 to 60.

Regarding the piston of the present invention, in particular, it is eagerly desired to select a material excellent in antigaspermeability so as to obtain high sanitary property as well as stably preserve a solvent for a long time, e.g. three years in a container (injection barrel). Compounding examples of such a rubber recipe are shown in the following Table 1: <tables id="tabl0001" num="0001"><img file="EP1547633A1_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP1547633A1_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP1547633A1_D0003.tif" /></tables>

The prefilled syringe of the present invention includes any type of prefilled syringes using the piston for a syringe illustrated above according to the present invention and the material or shape of the injection barrel part and other parts than the injection barrel, for example, the cap at the front end, injection needle part, plunger rod fitted to the rear end of the piston or the like is not particularly limited. For example, as the material of the injection barrel (-cum-container), plastics are generally used from the viewpoint of the surface roughness, such as cyclic olefinic resins, cyclic olefin-ethylene copolymers, polyethylene terephthalate type resins, polystyrene resins, etc. In particular, it is preferable to selectively use cyclic olefinic resins or cyclic olefin-ethylene copolymers (e.g. used for a sanitary container described in JP-B2-2914826).

The prefilled syringe of the present invention includes any type of syringes using the sealing stopper as a piston according to the present invention, that is, not only one as shown in Fig. 1(c), but also two compartment type syringes, e.g. as shown in JP-A-8-308688.

ADVANTAGES OF THE INVENTION

Since the sealing stopper or piston for a syringe according to the present invention has a skirt part provided with a backstop function, compressing of the piston can be carried out in an injection barrel, but drawing thereof cannot be carried out. Thus, according to the present invention, reuse preventive function can be given in economical and simple manner. That is, the prefilled syringe using the above described sealing stopper of piston for a syringe can be provided with the reuse-preventive function with a low cost and can be prevented from such a danger that a syringe having been thrown away is used again.