From the AMCAS Instruction Manual:
"Repeat (R)
This selection applies to each completed attempt for any course attempted more than once, unless the final grade initially received was Withdrawal or Incomplete.
A course entry must be made for each completed attempt of a repeated course, even if any mention of enrollment in the course has been removed from the transcript. In order to comply with the needs of medical schools, AMCAS includes all attempts of repeated courses in GPA calculations, even if they are not included in the school's GPA calculations.
If you take a college level course for which you already have been granted AP credit by the same institution, this course is considered a Repeat. For example, if you received AP credit for your AP Psychology course and took an Introduction to Psychology course at the same undergraduate instution, you should list Introduction to Psychology as a Repeat.
Do not select Repeat for courses designed to be repeated (e.g., Independent Study, Thesis, Chorus, etc)."