A 10-year-old boy is brought to the physician because of weakness and decreased appetite for 3 months. He weighs 30 kg (66 lb) and is 142 cm (56 in) tall; he has had a 2.3-kg (5-lb) weight loss since his last examination 6 months ago. He appears thin. Deep tendon reflexes are brisk. Chvostek's sign is positive. His serum calcium level is 6.5 mg/dL, and serum intact parathyroid hormone level is 190 pg/mL (N=9–65). In addition to calcium supplementation, which of the following is the most appropriate next step in management?
A) Oral phosphate supplementation
B) Oral vitamin D supplementation
C) Intranasal calcitonin therapy
D) Parenteral bisphosphate therapy
E) Parenteral parathyroid hormone therapy