Once you've done your job interview, you should follow up with a formal letter thanking them for interviewing you, and to ensure they know that you are eager to accept the position should it be offered to you.
You would be surprised how many people don't do this - and it really helps you to stand out from the other applicants.
A thank you letter for a Medical Assistant isn't really much different to one you would write for any other kind of job - here is a sample that will give you a good starting point for when you write your own:
(Date goes here)
ABC Dermatology Clinic
8960 Long Avenue
California, CA 95423
Dear Ms. Mason,
Thank you for setting aside the time to meet with me this morning regarding the Clinical Medical Assistant position currently available at the ABC Dermatology Clinic. I enjoyed our discussion and appreciate all of the information you shared with me about the role and its duties.
I would like to affirm my desire to accept this position should you offer it to me.
During the interview you pointed out that you require someone who is comfortable working in a demanding environment as the clinic receives more than 100 patients per day during peak times. During my Externship at XYZ Family Clinic, I gained a great deal of experience working for two specialists, each of whom saw an average of more than 35 patients per day, and I interviewed most of the patients prior to their specialist consultation. I feel that my experience, combined with my excellent results on the RMA exam, have given me the background needed to meet your high standards.
If you have any further questions for me, please do not hesitate to call or email me. Otherwise, I look forward to hearing from you.
Jane Smith, RMA
So there you have it. It's not really that hard or time consuming to write a thank you letter, and you will stand out from the crowd. I recommend that you write and send your letter no later than 1 day after your interview.