Parathyroid hormone changes following denosumab treatment in postmenopausal osteoporosis

Objective Denosumab is a new potent antiresorptive treatment of osteoporosis that can potentially induce a compensatory increase in parathyroid hormone (PTH) levels. We aimed to evaluate the alteration of PTH 1 and 6months after denosumab's administration with different regimens of calcium and vitamin D (Ca/D) supplementation. Design Prospective, multicenter, study in a relatively small, heterogeneous sample of postmenopausal women followed for 6months. Patients Forty seven postmenopausal women followed in 2 outpatient clinics, requiring onset or continuation of osteoporosis treatment. We administered 1g calcium carbonate and 800 IU cholecalciferol daily for 6 months (Group A) or the double dose for the first month followed by the 1g/800 IU Ca/D regimen for the next 5 months (Group B). Measurements Parathyroid hormone (PTH) alterations between and within groups, and their associations with serum Ca and bone markers. Results Parathyroid hormone (PTH) levels were significantly higher at month 1 and 6 only in Group A; Ca levels were significantly decreased at month 1 and returned to baseline values at month 6 within the same Group. The mean per cent change between month 1 and baseline for PTH [Delta(PTH1-0)] was significantly higher in Group A than B (63.5% +/- 2.82% vs -3.0% +/- 4.7%, P = 0.029).Delta (PTH1-0) was correlated with the reciprocal -changes of Ca (r(s) = 0.610; P = 0.002) and collagen type I C-terminal telopeptide (r(s) = -0.697; P = 0.003) only in Group A. Conclusions An increase in PTH should be expected, at least following the first administration of denosumab in common clinical practice. The effect of this compensatory onsequence in bone metabolism warrants further investigation.