A 48-year-old male with treatment-resistant major depressive disorder has failed adequate trials of three antidepressants from different classes and two augmentation strategies. He continues to endorse severe depressive symptoms with passive suicidal ideation but denies intent or plan. The PMHNP refers the patient for esketamine (Spravato) nasal spray treatment. Which of the following best describes the mechanism and required administration protocol for esketamine?