Method and device for fluid transfer in an infusion system

A method for fluid transfer in an infusion system, said method comprising the steps of:

• using a fluid transfer device to inject a medical substance into said infusion system via an injection port able to be sealed by a flexible barrier member, said fluid transfer device comprising at least a first member, a hollow needle attached to said first member, and a second member telescopically displaceable in relation to said first member;
• providing said fluid transfer device with a first end, and a second, opposite end having a flexible membrane,
• providing a drug bottle containing a fixed dose of said medical substance;
• attaching said first end to said drug bottle;
• coupling said second end to said injection port while pressing said flexible membrane against said flexible barrier member with a pressure sufficient for creating a double-membrane sealing;
• creating a fluid passage from said first end of said infusion system by telescopically displacing said first end in a direction towards said second end, thereby allowing said hollow needle to penetrate said flexible membrane and said flexible barrier member while being surrounded by said double-membrane sealing;
• and
• transferring said fixed dose from said drug bottle into said infusion system by means of creating and subsequently releasing a positive pressure inside said drug bottle.