SAT-752 The Calcium Bandits: A Case of Combination Lanreotide and Denosumab Induced Hypocalcemia.

Abstract

Disclosure: S. Sridhar: None. F. Waqar: None. A.W. Paracha: None. M. Ortiz: None. A. Ehsan: None. A. Siddiqui: None.Lanreotide, a somatostatin analog is used in the management of neuroendocrine tumors. Common side effects are gastrointestinal symptoms and injection site pain. Few case reports mention the impact of lanreotide on serum calcium.Denosumab used in treatment of osteoporosis has been reported to cause hypocalcemia in 2% cases, usually in the setting of prior hypocalcemia, renal impairment, bone metastases, prostate cancer, postmenopausal age or concurrent use of other agents that can decrease calcium.A 63-year-old woman with primary hyperparathyroidism, osteoporosis, hypovitaminosis D and gastrointestinal NET on lanreotide, presented to ER for new onset dyspnea, muscle cramps and weakness. Labs revealed serum calcium 4.7 mg/dL (8.4-10.2), magnesium 1.6 mg/dL (1.6-2.6), phosphorous 3.4 mg/dL (2.5-4.5), creatinine 1.95 mg/dL (0.6-1), eGFR 28 mL/min/1.73m2 (>60), albumin 2.6 g/dL (3.5-5.2), for a corrected Ca 5.8 mg/dL, ionized Ca 0.63 mmol/L (1.15-1.27), PTH 2157 pg/mL (15-65), 25-hydroxy vitamin D 29 ng/mL (30-100) and 1,25 dihydroxy vitamin D 79.9 pg/mL (19.9-79.3). Labs prior to hospitalization were Ca 8.4-10.3 mg/dL, PTH 74 pg/ml and 25-hydroxy Vit D 31 ng/ml.Intravenous calcium gluconate was administered. Oral calcium carbonate 1000 mg every 8 hours and vitamin D 5000 IU daily were started. Hypocalcemia gradually improved over next few days and she was discharged home.Etiology of her hypocalcemia was unclear. She was started on denosumab 18 months prior, and had maintained normocalcemia with the first two doses. The only outstanding observation was that she had received lanreotide just few days prior to her presentation. She had previously received lanreotide for four months without any problem. This was also the first time that she had received denosumab since initiation of lanreotide therapy. Hence, we hypothesized that consecutive administration of these two agents within a week of each other was the cause of her hypocalcemia. Post-discharge, Ca level stabilized on calcium carbonate 500 mg daily, however more than a month later, PTH remined high at 1427 pg/ml. To prevent recurrence, plan is for empiric calcium supplementation pre and post denosumab injection, while she remains on lanreotide, and to space both medications as feasible.In a study to evaluate the effect of lanreotide in acromegaly patients, short term treatment for 3 months caused significantly decreased serum calcium but increased PTH. Long term at 24 months, serum calcium normalized but increased PTH persisted. This suggests that lanreotide has long term effect on calcium homeostasis, likely due to intestinal calcium malabsorption contributing to secondary hyperparathyroidism. This study shows that lanreotide decreases serum calcium enough to trigger increased PTH secretion from parathyroid glands.Lanreotide should be considered a risk factor for hypocalcemia, particularly in patients receiving denosumab.Presentation: Saturday, July 12, 2025