A carousel configured to house a plurality of pump cartridges for a compounder system is provided. The carousel may include a plurality of cartridge pockets each having an extended portion that covers a portion of a cartridge and a bottom surface Shaving an extension with a recess. The bottom surface recess of each cartridge pocket may be shaped and sized to receive a needle housing of a pump cartridge in the cartridge pocket. A recess may be provided in the extended portion of each pocket that receives a protrusion that extends from a top surface of a backpack coupled to the pump cartridge to secure the pump cartridge in the cartridge pocket. The bottom surface recess may have an additional bottom surface that prevents actuation of the needle housing of the pump cartridge.