Abstract: The present invention provides an apparatus for introducing a reconstituted drug in a drug vial into a medical liquid while venting any gas within the vial to the atmosphere. The assembly includes a receptacle disposed in the middle of a fluid conduit for the medical fluid and which has an upper chamber and lower chamber. The assembly also has a cannula assembly which mounts upon and pierces a septum of the receptacle and also a pierceable stopper of the drug vial. The cannula assembly includes a pair of coaxial cannulas which pierce the stopper of the drug vial and establish a first flow path from the upper chamber to the drug vial and a second flow path from the drug vial to the lower chamber. The cannula assemble also includes a cannula that forms a vent passage in fluid communication with an upper portion of the vial, upon the piercing of the drug vial, with an end of the vent passage communicating with the atmosphere.