A 58-year-old woman is brought to the psychiatric emergency department by her husband. He reports she has barely eaten or spoken in 10 days. She has a known history of recurrent major depressive disorder with two prior hospitalizations. On examination, she is mute, exhibits waxy flexibility, maintains postures when passively positioned, and has a fixed stare. She intermittently displays stereotypic movements. Her BMI has dropped to 16.2, and labs reveal a BUN/creatinine ratio consistent with dehydration. She has not responded to lorazepam 2 mg IV given in the emergency department. Her prior records show she has failed adequate trials of three antidepressants and two augmentation strategies. Which treatment should be prioritized?