SUN-772 Severe Hypocalcemia and Incorrect Bisphosphonate Prescription

Abstract Disclosure: J. Kessler: None. C. Ezeanyika: None. M. Thompson: None. Background: Bisphosphonates are a first-line medication to treat osteoporosis with the potential to lower calcium levels; it is currently contraindicated in patients with preexisting hypocalcemia and bariatric surgeries.Clinical Case:A 61-year-old female with a past medical history pertinent for a thyroidectomy, biliopancreatic diversion surgery, Roux-en-Y gastric bypass, and osteoporosis presented to the emergency department on October 30, 2024, with paresthesia in both arms, fatigue, and sinus bradycardia after receiving an infusion of 5mg zoledronic acid (Reclast) for osteoporosis on October 15, 2024. Before the administration of Reclast, her serum calcium was 8.4 mg/dL (normal range of 8.6 - 10.3 mg/dL) and the rheumatologist administered the medication despite the contraindication of prior bariatric surgeries and hypocalcemia. Her serum calcium in the emergency department was 6.5 mg/dL despite currently taking oral calcium supplementation, 1200mg calcium citrate three times daily. She was provided 2g IV calcium gluconate during her visit; repeat CMP showed a calcium of 10 mg/dL and she was informed to follow up with her primary care doctor in 2-3 days. On November 4, 2024, she returned to the emergency department with a similar presentation and labs indicating a calcium of 6.4 mg/dL. She endorsed chest tightness and perioral numbness. Her EKG at the time reported a QTc of 474 indicating a concern for prolongation due to hypocalcemia. The patient was admitted and received 1g of IV calcium gluconate twice. PTH, intact levels ordered during admission measured at 75 pg/mL (normal range of 18.5 – 88.0 pg/mL) indicating a previously masked hypoparathyroidism due to poor reactivity of PTH to severe hypocalcemia. Vitamin D, 25-Hydroxy, total (normal range of 30-100 ng/mL) measured 56 ng/mL within normal limits, and phosphorus (normal range of 2.5 -4.9 mg/dL) measured 5.2 mg/dL supporting the diagnosis of masked hypoparathyroidism. She remained in the hospital for two days where she received 2g IV calcium gluconate every two hours with 1000 mg calcium carbonate tablets. Before discharge, her calcium levels trended up to 8.5 mg/dL and endocrinology added calcitriol 0.25 mcg daily and a renal function panel three days after beginning the calcitriol. The patient was advised to continue calcium citrate 1200 mg tablet three times daily and to follow up with her endocrinologist to maintain adequate calcium levels. Endocrinology’s final assessment is that the masked hypoparathyroidism is due to absorptive issues from prior bariatric surgeries, which contraindicated the administration of Reclast, as the patient is responding well to IV but not her oral supplementation regimen. Conclusion: This is a rare case demonstrating the wrongful prescription of a bisphosphonate to prevent osteoporotic fractures in a preexisting hypocalcemic patient resulting in severe short and long-term medical concerns. Presentation: Sunday, July 13, 2025