Endocrine Abstracts

Introduction: Primary hyperparathyroidism (PHPT) is a state of increased bone turnover that can result in secondary osteoporosis. Antiresorptive treatment can be used to preserve bone mineral density (BMD). We compared the impact of zoledronate and denosumab on bone-related biochemical parameters.

Methods: We analyzed interim data from our ongoing randomized trial on osteoporotic postmenopausal women with PHPT who are being treated with either zoledronate 5 mg i.v. once a year (ZOL group) or with denosumab 60 mg s.c. every six months (DMAB group) (ClinicalTrials.gov Identifier NCT04085419). Here, we compare the serum calcium levels (S-Ca), intact parathyroid hormone (iPTH), and bone turnover markers at baseline and 3 months after the start of the treatment.

Results: We enrolled 40 female patients with a mean age of 73.0 (7.8 S.D.) years and 22.6 (10.0) years from menopause with a BMI of 27.77 (5.1) kg/m² and with osteoporosis: BMD at a lumbar spine (LS) 0.833 (0.134), total hip (TH) 0.736 (0.117), femoral neck (FN) 0.624 (0.084), distal third radius (1/3R) 0.494 (0.069) g/cm² and trabecular bone score (TBS) 1.190 (0.127). After randomization, 20 women received zoledronate (ZOL group) and 20 denosumab (DMAB group). Three months (3M) after the treatment, there was a statistically significant decrease of serum calcium (S-Ca) in both groups (DMAB: baseline S-Ca 2.72 (0.16) vs 3M S-Ca 2.65 (0.18) mmol/l; P=0.045, ZOL: baseline S-Ca 2.72 (0.1) vs 3M S-Ca 2.64 (0.12) mmol/l; P<0.01). No significant difference in S-Ca decrease between the groups was detected. Similarly, there was a significant increase in iPTH levels in both groups but no statistically significant difference between the groups: (DMAB Δ iPTH 61.91 (126.93) vs ZOL Δ iPHT 30.24 (56.84) ng/l; P=0.31). Bone turnover markers decreased significantly in both groups with greater decline of CTX and bone-specific alkaline phosphatase (BAP) in DMAB group (DMAB Δ CTX 0.952 (0.639) vs ZOL Δ CTX 0.556 (0.439) μg/l; P=0.03 and DMAB Δ BAP 19.92 (8.51) vs ZOL Δ BAP 12.99 (9.3) μg/l; P=0.03). The apparent numerical difference in P1NP was not statistically significant: DMAB Δ P1NP 75.45 (33.87) vs ZOL Δ P1NP 55.12 (32.52) μg/l; P=0.06.

Conclusion: Within the first three months of treatment, our data show a greater reduction in bone turnover markers in the DMAB group than in the ZOL group. S-Ca decreased, and iPTH increased in both groups without significant differences between the groups.