What teaching techniques can be used, in teaching students from a medical background, to improve their programming?
To get the premedical students involved you can tell them that by the end of the course they will be able to dissect a program. It may not be as gross as a frog, but it will be more interesting. Unlike the frog, when done dissecting the program they can bring it back to life.

The next thing requires that you mean what you say, and follow through with actions that match. Tell the class that their marks in the course will be based on their performance in the course and their apprehension of the course material, not upon their major or program of study.

Final thing is to forget which students are pre-med, chemistry majors, fine arts students, or comp-sci majors, and teach the class as if all the students are willing and able to learn.

The one thing that did catch my eye in the question was that the students in question have no basic concepts of programming. That causes me to wonder if some students are taking a course which should have a prerequisite course and does not, or if the course has been designed, unintentionally perhaps, based on the premise that incoming students have those basic concepts even though it is listed as an entry course.

Perhaps it has been the history of the course that students arrived with prior experience even though it was an entry course, and the faculty has grown accustomed to that and adjusted the course accordingly.