Fill facilitating unit dose injection cartridge and filling method

Abstract

A unit dose injection cartridge (e.g., needleless injection cartridge) includes an elongated chamber, a sealable discharge outlet (e.g., nozzle orifice) and a piston seal slidable within the chamber from a proximal end region to a distal end of the chamber. The piston seal is movably securable at a first position within the proximal end region, wherein the chamber is fillable with medicament by way of a passageway extending past the piston seal from a proximal side to a distal side thereof. During filling, air is allowed to escape from the chamber through the same passageway used for filling, or a second similarly arranged adjacent passageway. Once a unit dose of medicament is metered into the chamber, the piston seal may be moved slightly distally to a second position within the proximal end region, whereby the chamber is sealed-off from the passageway by the piston seal. During this movement of the piston seal, and before the chamber is sealed-off, any air remaining in the chamber is allowed to escape through the passageway (or second passageway), avoiding the need for leakage of air and/or medicament through the orifice of the discharge nozzle. The passageway(s) may be provided between the plunger and an adjacent laterally recessed chamber wall portion, or alternatively as discrete passageways through the chamber-forming wall structure.