A method and system for sequentially dispensing a non-user settable dose of one medicament followed by a user-settable dose of a primary medicament. The system may include a dual cross-section, floating piston arranged to facilitate first delivering all or substantially all of a given medicament (e.g., a secondary medicament) through an output needle and then thereafter delivering yet another medicament (e.g., a primary medicament) through the same output needle in a single injection step. The dual cross-section, floating piston of the system also reduces or limits ullage left in the medicated module relative to the amount of the secondary medicament dispensed from the system.
