The ornamental design for a metered-dose inhaler mouthpiece, as shown and described.
FIG. 1 is a left side, front, and top perspective top view of a metered-dose inhaler mouthpiece, showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken line showing of the cartridge in FIGS. 1-4 depict environmental structure that forms no part of the claimed design. All other broken lines depict portions of the metered-dose inhaler mouthpiece that form no part of the claimed design.