J Clin Endocrinol Metab. 2021 Jun 22:dgab457. doi: 10.1210/clinem/dgab457. Online ahead of print.
CONTEXT: Bisphosphonates are effective for hypercalcemia of malignancy (HOM). Efficacy and safety data for bisphosphonates in parathyroid hormone-related hypercalcemia (PTHRH) are rare, including pamidronate, which is not indicated for this condition.
OBJECTIVE: To evaluate the efficacy and safety of pamidronate for moderate-to-severe PTHRH.
DESIGN: Retrospective case-control study.
SETTING: Tertiary care medical center.
PATIENTS: Adults hospitalized with serum calcium levels ≥12mg/dL, 29/10/2013-17/12/2019.
INTERVENTIONS: Etiology was categorized as PTHRH or PTH-independent. Clinical and laboratory data of PTHRH patients treated with pamidronate (PTHRH-Pam+) were compared to pamidronate-untreated counterparts (PTHRH-Pam-).
RESULTS: Thirty-four patients with 37 hospitalizations for PTHRH (pamidronate-treated and untreated) met the inclusion criteria. Pamidronate was given in 24/37 cases (64.8%). Admission serum calcium levels for the PTHRH-Pam+ group were higher than for PTHRH-Pam- (14.4mg/dL vs. 13.0mg/dL, p=0.005). Median total pamidronate dose was 60mg (range 30-180mg) in the treated group. Serum calcium decreased 3.5mg/dL for PTHRH-Pam+ vs. 1.6mg/dL for PTHRH-Pam- (p=0.003). No PTHRH-Pam+ patients developed hypocalcemia or acute kidney injury. Nadir serum phosphorus levels were lower in the PTHRH-Pam+ vs. PTHRH-Pam- group (1.7mg/dL vs. 2.4mg/dL, respectively, p=0.005). Three PTHRH-Pam+ patients developed severe hypophosphatemia; all resolved with intravenous and oral supplementation. Seventeen patients underwent parathyroidectomy, of whom 10 received pamidronate within 28 days preoperatively. Post-operatively, 4 developed hypocalcemia and 3 hypophosphatemia.
CONCLUSIONS: This study demonstrates that pamidronate is effective and safe for treating PTHRH, while ensuring close laboratory monitoring of calcium and phosphorus metabolism. Larger, prospective studies are needed to establish the role of pamidronate and other potent bisphosphonates in moderate-to-severe PTHRH.