Put on a pair of clean white cotton gloves.
Mount the drawing on an acid-free sheet of museum board with archival mounting tape. Prepare a beveled matt with an interior size 1-2 cm smaller than your paper. Attach the matt to the museum board with one strip of archival tape along the top edge. Place a piece of 5 mm thick plexiglas on the matt and tape to the museum board along the sides. Place the entire object in a thick plastic bag, fold down the opening several times while pressing out the air and tape shut with plastic packaging tape.
Then place the packaged drawing into a wooden shipping box with custom cut styrofoam spacers so that it cannot move. Put a sachet of silica gel under the museum board in a small space you have carved out of the foam. Put a foam sheet on top of the matt and close the box with screws. Using indelible marker (or hand-cut stencil for the authenticity) write FRAGILE GLASSWARE. HANDLE WITH CARE. on every side of the box. Label with the contents, attach shipping label and place in the loading bay for the (insured) delivery company to pick up.
DIY CHEAP VERSION
In an emergency I would use waxed paper like the kind used for baking to cover the sheet of paper. Fold it over the top, tape with removable masking tape to the back of the drawing. Use multiple rows that overlap and then sandwich the drawing between two sheets of cardboard that are 1.5 times bigger than the drawing. Put the whole thing in a garbage bag that you then wrap airtight and tape closed.