A container (200) for containing a coupling medium for transdermal delivery of a medicament and a transducer unit (100) for use with the container (200) are disclosed. The transducer unit (100) has a transducer (108) with an output face (110), and the container comprises a chamber (214) for receiving the coupling medium and a contact surface (212) for contacting the output face (110) of the transducer (108). The container (200) is attachable to the transducer unit (100) and is arranged such that, upon attachment of the container (200) to the transducer unit (100), an acoustic coupling for ultrasound transmission is formed between the output face (110) of the transducer (108) and the contact surface (212).