Cartridge and pump with axial loading

The present invention concerns a medication pump for use with a medication cartridge that is loaded using a drive rod of the medication pump. In one embodiment, the drive rod includes an interface structure defining a first channel where the first channel has an axial portion disposed parallel to an axis of the drive rod and a locking portion disposed in a circumferential direction around an outer surface of the drive rod. In another embodiment of the invention, the drive rod includes a visual indicator at an interface end of the drive rod, so that when the interface structure of the drive rod is coupled to a plunger of a medication cartridge, the visual indicator will not be seen, to provide a way to check for secure coupling of the drive rod to the plunger. In its embodiment, the outer housing of the medication pump includes a window into a cartridge housing to allow a view of the visual indicator if it is not attached to the plunger. In another embodiment the medication pump includes a pump cap that has guides located on an interior surface. These guides engage axial guides on a medication cartridge, so that when the pump cap is rotated, it causes rotation of the medication cartridge so that the medication cartridge is rotated into engagement with the interface structure of the drive rod.