A 21-year-old woman is admitted to the ED in a coma. She is accompanied by her husband, who states that she had a seizure. The patient is 1 week postpartum. Her vital signs are blood pressure 180/128 mmHg, pulse rate 120 beats/minute, and respiratory rate 12 breaths/minute. The physician diagnoses eclampsia. After the initial management of this patient, the nurse would expect the physician to order which medication?