A medical device comprises a medical monitoring or treatment device configured to provide a monitoring or treatment operation on a user, the medical monitoring or treatment device operable with an insertion needle (5635 5735) and a pierceable membrane (5640 5740) containing an agent (5650 5750), the pierceable membrane (5640 5740) positioned to be pierced by the insertion needle (5635 5735) during operation of the medical monitoring or treatment device and to allow the insertion needle to cause some of the agent to be carried from the pierceable membrane (5640 5740) to the user.