Aminobisphosphonates impair osteoclast cell function and reduce bone remodelling rate. It has been speculated that atypical femoral fractures in patients on bisphosphonates are the result of impaired bone remodelling.
The primary aim of this prospective study was to assess levels of bone remodelling in patients with osteoporosis on aminobisphosphonate therapy by measurement of bone turnover markers. The secondary aim was to assess the adequacy of concomitant vitamin D supplementation.
We identified 77 subjects (6 males) consecutively from our endocrine practice; details of aminobisphosphonate, vitamin D and calcium therapy were recorded. Serum parathyroid hormone (PTH), 25-hydroxyvitamin-D (25OHD), bone-specific alkaline phosphatase (bone ALP) and tartrate-resistant acid phosphatase (TRAP5b) were measured.
The mean age of subjects was 71.3±9.3 years. Mean duration of bisphosphonate therapy was 5.8±4 years. Only 2 subjects suppressed bone ALP to less than the lower limit of the normal reference range, and none suppressed TRAP5b on aminobisphosphonate therapy. Mean 25OHD was 78±26 nmol/l; 41 subjects had levels >75 nmol/l and only 10 had levels <50 nmol/l of whom 7 were taking 400 IU/day or less.
Mean PTH was 43.9±19 ng/ml, and correlated with age (r=0.32), 25OHD level (r=−0.44) and duration of therapy (r=0.23, P<0.01).
In conclusion, aminobisphosphonate therapy is not associated with over-suppression of bone turnover. Continuous low dose vitamin D supplementation achieved more than adequate vitamin D status if taking 800 IU daily.