A 35-year-old female with obsessive-compulsive disorder has shown excellent response to fluvoxamine 200 mg daily over the past 6 months. She now presents with a new diagnosis of migraine headaches, and her neurologist has started tizanidine for acute muscle tension associated with her migraines. The PMHNP reviews the medication list and identifies a critical drug interaction. Which of the following best explains the pharmacokinetic concern with the combination of fluvoxamine and tizanidine?