MSFinals-5382

A 55-year-old man visits his GP clinic complaining of chronic constipation that has persisted for several years. He reveals that he has not had a bowel movement in ten days. The patient has a medical history of atrial fibrillation, type II diabetes mellitus, gastro-oesophageal reflux disease, and paranoid schizophrenia. He is currently taking apixaban, clozapine, digoxin, metformin, and lansoprazole. During the physical examination, the doctor notes a hard, non-tender abdomen and fecal impaction upon PR examination. Which of the medications listed above is likely contributing to his long-standing constipation?