Such systems usually comprise two hermetically closed vials, one containing an active product generally in the form of a lyophilized or otherwise dried powder or granulate or a liquid and the second containing the liquid in which the active product is dissolved or suspended. The system further comprises a connecting piece for temporary connection of the two vials.

The active product is usually contained in a glass vial which is closed by an elastic rubber stopper inserted in the neck of the vial. In the commonly used systems the stopper has in its axis a channel which is covered by a thin, perforable airtight membrane, such as aluminium, which is glued or welded onto the top surface of the stopper.

The second vial containing the liquid is more often made of plastic material and is closed by a dropper with a tip having a diameter smaller than the said channel through the stopper. When being connected to the first vial the dropper perforates the membrane in such a way that airtightness is provided between the two vials.

The presently known stoppers have the disadvantage that they consist of two pieces namely the stopper as such and the membrane affixed to it. To produce such a stopper several consecutive manufacturing steps are necessary resulting in a relatively expensive product.

Another problem is the risk of having aluminium particles in the reconstituted solution when the aluminium foil is perforated at the time of use. This would constitute a danger of the final user, especially if the product is for ophtalmic use or skin treatment around the eyes.

The aim of the present invention is to provide a stopper whose manufacture is less complicated and which is, thus, less expensive, harmless and environment-friendly when recycled.

According to the invention this is achieved by a stopper consisting of one piece of plastic rubber material which has a concentrical portion whose axial thickness is reduced to a membrane which has radially arranged cuts constituting defined breakage lines during its tearing.

According to a preferred embodiment of the invention two curved projections are arranged on the upper surface of the stopper to avoid their sticking together when manipulated by machines. Another preferred embodiment has an annular projection on the lower surface of a flange-shaped portion of the stopper. A further preferred feature is a cut-out portion in the lower stopper part.

In the following preferred embodiments of the invention are described with regard to the accompanying drawings, wherein Fig. 1 shows a side view of a stopper, Fig. 2 shows the interior of the stopper from below, Fig. 3 is a top view of the stopper of Fig. 1 The stopper 1 shown in the figures is made of plastic rubber material. It is generally cylindrical and has an

upper flange-shaped portion 2 and a lower skirt-shaped portion 3. In its interior it is provided with a coaxial cavity 4 extending from the lower surface 5 up almost to the top surface 6 leaving a thin membrane-like layer 7 of the stopper material to keep the closing capability of the stopper.

The skirt-shaped portion has a cut-out section 4a which extends from the lower surface 5 to about 2/3 of the entire height of the stopper. The width of the cut-out section represents an angle of about 20°. The cut-out section facilitates the adaptation of the outer cylindrical dimensions of the skirt-shaped portion 3 to the inner wall of the collar of the vial.

The membrane-like layer 7 is provided with four radially arranged cuts 8 which meet in the stopper axis and which extend partially through the layer 7 without entirely perforating it to keep the airtightness of the stopper.

When during connection of a vial, which is closed by the stopper 1 with another vial having a dropper the membrane is perforated the cuts constitute predefined breakage lines which guarantee tight attachment of the membrane-like layer flaps to the dropper to keep airtightness during connec- tion. After removal of the other vial the flaps close the perforation to essentially retain tightness.

The lower surface of the flange-shaped portion 2 is provided with an annular projection 9 rising slightly above the surface. This projection serves to enhance the air tightness provided be the skirt-shaped portion 3.

The top surface 6 of the stopper is equipped with two arcuate projections 10 rising slightly above the surface level. These projections serve to avoid pairs of stoppers sticking together with their top surfaces which would be

undesirable for machine manipulation. The shape of the projections could of course differ from being arcuate.

The stopper is particularly useful in connection with the dual vial connector described in PCT/EP 97/04660 and PCT/EP 04290 in which however the membrane and the sealing rings would be eliminated. This combination would be a preferable alternative for the user who due to habit or in view of manufacturing restrictions intends to remain with a stopper solution.