The present invention relates to an apparatus (100) for the delivery of an active agent through a body surface of a mammal comprising: (a) a housing (102) with a delivery orifice through the housing; (b) a reservoir (120) within the housing for containing the active agent where the reservoir is in communication with the delivery orifice; (c) an electrode within the reservoir where the electrode (112) is capable of being in electronic communication with a current supply unit; and (d) a sensor (118) within the reservoir where the sensor is capable of being in electronic communication with the current supply unit; wherein the current supply unit can modify an electric parameter at the electrode based upon feedback from the sensor.