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 6 months 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 6 months.

PATIENTS: Forty seven postmenopausal women followed in 2 outpatient clinics, requiring onset or continuation of osteoporosis treatment. We administered 1 g calcium carbonate and 800 IU cholecalciferol daily for 6 months (Group A) or the double dose for the first month followed by the 1 g/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 [Δ(PTH1-0 )] was significantly higher in Group A than B (63·5% ± 28·2% vs -3·0% ± 4·7%, P = 0·029). Δ(PTH1-0 ) was correlated with the reciprocal Δ-changes of Ca (rs  = -0·610; P = 0·002) and collagen type I C-terminal telopeptide (rs  = -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.