A 42-year-old male with treatment-resistant schizophrenia has been stable on clozapine 400 mg daily for two years with a trough level of 420 ng/mL. He develops comorbid obsessive-compulsive symptoms that significantly impair his daily functioning. The treating psychiatrist initiates fluvoxamine 50 mg daily. Three weeks later, the patient presents with increased sedation, hypersalivation, and orthostatic dizziness. A repeat clozapine level returns at 1,050 ng/mL. Which of the following best explains the pharmacokinetic mechanism responsible for this clinical scenario?