IMPROVED MEDICATION DELIVERY PEN

A medication delivery pen includes a housing having an actuator disposed in the proximal end of the housing for setting and administering a dosage of medication, a medication-containing cartridge assembly having a cartridge with a pierceabl y sealed distal end, an open proximal end removably attachable to the distal end of t he housing, and a piston in sliding, fluid tight engagement within the cartridge. A driv e mechanism is coupled between the actuator and the cartridge to exert an axial force on th e piston to inject the set dosage of medication. The actuator triggers the drive mechani sm to administer the injection of medication held in the cartridge and a processor is coupled to the actuator to determine a value equal to the dosage set by the actuator.