At the end of your actual interview, if you are interviewing one-on-one, ask for your interviewer’s business card or contact information. You will want to send them a nice note (usually a handwritten card) thanking them for their time. When writing your card, try to remember specific details about them and mention these details in your card. For example, if they mentioned that they are doing research in a certain field, you can say something like, “I hope everything goes well with XYZ project”.
It is also good to have your interviewer’s contact information just in case you want to send them any updates. They could potentially serve as your advocate to the admissions committee. You can ask them questions via email but be sure not to annoy them.
After the majority of your interviews are over, if you have one school that you really want to attend, it would be wise to send a letter of intent. This is to inform one specific school that it is your top choice for medical school. You can also send update letters to each of the schools you interviewed at to highlight more recent significant activities or accomplishments.