Endocrine Abstracts

Introduction: Antiresorptive treatment can preserve bone mineral density (BMD) in patients with primary hyperparathyroidism (PHPT) when surgery is not feasible or desired. We aimed to compare the impact of zoledronate vs denosumab on bone-related biochemical parameters in this population.

Methods: We analyzed preliminary data from our ongoing randomized trial on osteoporotic postmenopausal women with PHPT who are being treated either with zoledronate 5 mg iv once a year (ZOL group) or with denosumab 60 mg sc every six months (DMAB group) (ClinicalTrials.gov Identifier NCT04085419). Here we compare their laboratory parameters and bone turnover markers at baseline and three months after starting the treatment.

Results: We studied 21 osteoporotic females (with mean BMD at LS 0.841 (SD 0.132), TH 0.749 (0.117), FN 0.645 (0.084), 1/3R 0.500 (0.066) g/cm²) aged 76.2 (7.1) years and 26.9 (9.7) years from menopause with BMI 28.78 (4.4) kg/m². Eight patients received zoledronate (ZOL), and thirteen were treated with denosumab (DMAB). There were no statistically significant differences in baseline characteristics between the two groups. Three months (3M) after starting treatment, there was a statistically significant fall in serum calcium (S-Ca) levels in the ZOL group only (baseline S-Ca 2.7 mmol/l (0.1) vs. 3M S-Ca 2.6 mmol/l (0.1); P=0.033). Intact parathyroid hormone (iPTH) values increased in both groups; the increase did not differ between the two groups (ZOL Δ iPTH 44.28 (113.54) vs. DMAB Δ iPHT 42.84 (63.33); P=0.9). Baseline 25 OH vitamin D was similar in both groups, with the average value 56.8 (18.8) nmol/l, and remained unchanged after treatment. Bone turnover markers decreased statistically significantly in both groups (ZOL CTX baseline 0.495 (0.3) vs. 3M 0.098 (0.12) μg/l; P<0.01; ZOL P1NP baseline 74.5 (28.3) vs. 3M 19.9 (9.9) μg/l; P<0.01; DMAB CTX baseline 0.89 (0.77) vs. 3M 0.01 (0.01) μg/l; P<0.01; DMAB P1NP baseline 79.7 (34.4) vs. 3M 14.05 (4.9) μg/l; P<0.01). The differences between the groups were not statistically significant (ZOL Δ CTX 0.4 (0.3) vs. DMAB Δ CTX 0.88 (0.77) μg/l; P=0.1 and ZOL Δ P1NP 54.55 (24.86) vs. DMAB Δ P1NP 65.65 (32.08) μg/l; P=0.4).

Conclusion: Preliminary analysis showed a significant decline in calcium levels only in the ZOL group. Bone turnover markers significantly decreased in both groups—the apparent numerical difference in decrease after ZOL vs after DMAB was not statistically significant.