A female patient has primary adrenal insufficiency. She is on hydrocoisone 15 mg a day and fludrocoisone 0.1 mg daily. She becomes acutely ill after eating raw oysters. She has severe, "cramping" abdominal pain and profuse watery diarrhea. Vital signs show a hea rate of 135 bpm, respiration rate of 28 bpm, blood pressure of 72/25 mm Hg, and temperature of 38.1degC. The exam shows tachycardia, dry oral mucosa, clear lungs, and diffuse abdominal tenderness. A rectal exam is heme negative. There are no skin rashes. Which of the following is most appropriate for the initial management of this patient?