Patient-controlled analgesia security attachment for a medication infusion system

A device (40) for use as an attachment for use in a medication infusion system having a main pump unit (20) containing a prime mover and a control system for controlling the operation of a disposable cassette (22) containing a fluid pump which is mounted on the main pump unit (20) the device (40) includes both a compartment (120), 126) for securely storing the medication supply (111) and means for preventing the cassette (22) and the fluid line between the storage compartment (120, 126) and the cassette (22) being removed or tampered with. The device (40) is locked onto the main pump unit (20) with a single key (76) operated lock (74) which also locks the cassette (22) in a position on the main pump unit (20), the compartment (120, 126) for storing the medication supply (111), and a cover (70) sealing the fluid line. The system is capable of being used with a variety of fluid sources including both syringes (111) and bags (130).