The patient is a 26-year-old male graduate student presenting to his health maintenance organization. He is having ongoing difficulty completing his thesis. When he is working on the computer, he finds it necessary to print out and save every draft of his paper. Even though he realizes that it is unnecessary to do so, he feels compelled to read and reread all of his versions in case he made a mistake. As a result, he has been unable to move forward with his dissertation. He is consumed with doubts about his thesis, but at the same time he cannot throw away discarded sections. In fact, his apartment contains stacks of paper spread throughout his rooms. He understands that these thoughts and behaviors are "not rational," and he is greatly distressed by them and the problems they have caused.
Which of the following would be the most appropriate pharmacotherapy for his condition?