Review Question - QID 216241

A 29-year-old woman presents to the emergency room with a 4-day history of abdominal pain. She states that the pain has become increasingly severe over the last 4 hours, and she is now very nauseated. She has no known medical problems and takes a multivitamin. She has a history of irregular menstrual cycles and is not sure when her last period was. She works as a jeweler and does not smoke cigarettes, drink alcohol, or use drugs. Her temperature is 99.5°F (37.5°C), blood pressure is 90/50 mmHg, pulse is 125/min, and respirations are 24/min. Her body mass index (BMI) is 25 kg/m^2. Abdominal examination reveals diffuse tenderness to palpation and guarding. A urine beta-hCG test is positive and a serum hCG is 17,050 mIU/mL. A transvaginal ultrasound reveals an empty uterus and free fluid in the posterior cul-de-sac of the pelvis. Which of the following is the most appropriate next step in management?