Abstract: A drug delivery device (1), comprising a delivery unit (3) including a drug container (6) comprising a barrel portion (6a) and a plunger (12) slidably mounted within the barrel portion and sealing the drug (78) within the container at one end of the barrel portion, and a drive unit (4) comprising a pneumatic flow system (74) and a pneumatic pumping system configured to pump air via the pneumatic flow system (74) to a space behind the plunger to generate a gas pressure to advance the plunger in the container during drug delivery. The drug delivery device comprises a sealing adaptor (9) mounted on an end of the drug container facing an outer side of the plunger, the sealing adaptor (9) comprising a sealing plug (23) inserted inside an end of the barrel portion, the sealing plug (23) comprising an orifice (26) configured for pluggable sealing connection to a gas channel connector (40) of the pneumatic flow system.