Physics 141L and 142L are usually taken by prehealth students; 151L and 152L are taken by Pratt students and 161L and 162L by Physics majors. Physics 141L, 151L and 161L generally teach the same material, although the focus and applications are different. The same is true for Physics 142L, 152L and 162L. It is acceptable to mix and match these courses (e.g. combine Physics 151L and 142L). All courses require a background in Calculus; check the course descriptions for details.
Medical schools will accept both Algebra-based and Calculus-based Physics. If you decide to take Algebra-based Physics over the summer at another university, be sure that it covers the same material that is taught here. You can request transfer credit for these courses, or you might choose to not transfer the courses to Duke. When you apply to medical or other health professions schools, you will be required to send a transcript from every college or university you have enrolled, so they will see the courses and grades. If you are declaring a major that requires Physics, be sure your Physics classes taken away will count. Algebra-based Physics classes that transfer to Duke will usually transfer as Physics 100.
Pratt students should note that Physics 151L and 152L do not completely cover all of the material tested on the MCAT, so you should self-review if needed.