A system for delivering a drug to a patient according to the preferred embodiment of the present invention is shown as being of modular construction including a control module and a reservoir module. The reservoir module is removably secured to the control module by a removable hinge member at one end and a locking member at the other end. The reservoir module includes a pressure plate upon which a tube extending from a drug container bag to the patient is supported. The control module includes a pumping mechanism including a camshaft which reciprocates valves and an expulsor in the control module engaging and interacting with the tube located on the pressure plate for forcing the drug from the drug container bag to the patient. In its most preferred form, the pressure plate includes standoffs which abut with the pump chassis for insuring proper spacing maintenance between the pressure plate of the reservoir module and the control module. In another aspect of the present invention, an occlusion detector is provided in the system including a switch on the control module which also engages and interacts with the tube of the reservoir module. The occlusion detector interrupts operation of the pumping mechanism in the event of reduced pressure in the tube.