Parathyroid hormone levels following denosumab vs. zoledronic acid therapy for osteoporosis

The objective of this retrospective, database study was to characterize the rate, magnitude and timeline of increases in parathyroid hormone (PTH) levels post-denosumab (DMAb) vs. zoledronic acid (ZA) injection in patients with osteoporosis and near normal baseline PTH. Included were osteoporotic females, >= 50 years, initiating treatment with 60 mg DMAb or 5 mg ZA. PTH levels within 6-months post-DMAb or 12-months post-ZA injection were extracted from the electronic database of a 4.5 million-member health maintenance organization. The indication for PTH measurements was unknown. Exclusion criteria were creatinine >2 mg/dL, vitamin D < 50 nmol/L or parathyroid hormone level > 1.5 x upper limit of normal (ULN). Among 3317 women, 1992 received DMAb and 1325 ZA. The DMAb group was older (73.3 +/- 8.5 vs. 69.8 +/- 8.6 years, p < 0.001) and more patients treated with DMAb compared with patients treated with ZA had prior non-vertebral fractures (7.7 % vs. 5.2 %, p < 0.01) and had previously been treated with osteoporosis medication (56.3 % vs. 50.3 %, p < 0.001). Among the patients, 14.9 % had at least one post-treatment PTH > 1.5 ULN. Of 7273 post-treatment PTH tests, 62.6 % were within normal limits, while 24.8 % were mildly elevated at 1.01-1.5 ULN. Two-months after both treatments, >1.5 ULN PTH levels peaked at similar to 20 %. Elevated PTH was associated with eGFR < 60 mL/min/1.73 m(2) and comorbidities. In conclusion, most PTH levels post-DMAb or ZA in osteoporotic patients with baseline PTH < 1.5 ULN, were within normal range. PTH increased to >1.5 ULN in 14.9 % of patients; peaking in the first 2-months post-treatment and declining thereafter. Elevated PTH may be related to anti-resorptive effects and is not medication specific. PTH measurements in the first few months post-DMAb and ZA therapy should be limited.