An adaptor for coupling with a medical container having a collar closed by a septum, said septum having an outer surface directed towards the outside of the medical container, the adaptor comprising: - a tubular body substantially closed at its distal end with a transversal wall provided with a central hole from which extends a hollow spike in the distal direction for passage of a fluid, a plurality of circumferentially distributed chambers extending from said transversal wall in the proximal direction, said chambers being closed at their proximal end by a pierceable elastomeric piece, each chamber being connected to said hollow spike by a radial channel provided with a closure member, said closure member being capable of transitioning from a locked state, in which it closes the radial channel, to an open state in which it does not close said radial channel, each chamber being filled with decontaminated air and each closure member being in a locked state in a storage state of said adaptor, - said tubular body further receiving an intermediate piece located proximally with respect to said pierceable elastomeric piece, said intermediate piece comprising a plurality of circumferentially distributed through holes, each through hole being aligned on one chamber of said plurality of chambers, - a selecting member located proximally with respect to said intermediate piece, said selecting member comprising a closure wall provided with one opening, said selecting member being capable of rotating with respect to said intermediate piece, so that said opening is capable of being successively aligned with each of said through holes, - a gripping member for securing the adaptor to the medical container, so that the distal surface of said transversal wall is brought in contact with the outer surface of said septum when said adaptor is secured on said medical containerand said hollow spike pierces said septum. - a tubular body substantially closed at its distal end with a transversal wall provided with a central hole from which extends a hollow spike in the distal direction for passage of a fluid, a plurality of circumferentially distributed chambers extending from said transversal wall in the proximal direction, said chambers being closed at their proximal end by a pierceable elastomeric piece, each chamber being connected to said hollow spike by a radial channel provided with a closure member, said closure member being capable of transitioning from a locked state, in which it closes the radial channel, to an open state in which it does not close said radial channel, each chamber being filled with decontaminated air and each closure member being in a locked state in a storage state of said adaptor, - said tubular body further receiving an intermediate piece located proximally with respect to said pierceable elastomeric piece, said intermediate piece comprising a plurality of circumferentially distributed through holes, each through hole being aligned on one chamber of said plurality of chambers, - a selecting member located proximally with respect to said intermediate piece, said selecting member comprising a closure wall provided with one opening, said selecting member being capable of rotating with respect to said intermediate piece, so that said opening is capable of being successively aligned with each of said through holes, - a gripping member for securing the adaptor to the medical container, so that the distal surface of said transversal wall is brought in contact with the outer surface of said septum when said adaptor is secured on said medical containerand said hollow spike pierces said septum.