Surrogate markers in assessment of bisphosphonate effectiveness in osteoporosis treatment (bone mineral density, bone turnover markers)

A review of the literature which summarizes our knowledge on the use of surrogate markers of the osteoporosis treatment effectiveness when on bisphosphonate (BP) therapy. Bone mineral density (BMD) and markers of bone turnover, which have been shown to be associated with the clinical fracture end point, have been used as surrogate criteria for the effectiveness of treatment of osteoporosis in randomized controlled trials. When prescribing BP for the treatment of osteoporosis, BMD measurement every 12 months by dual-energy x-ray absorptiometry (DXA) is the well-described surrogate marker of BP efficacy. At the same time, stabilization of BMD is also a criterion for the treatment effectiveness since changes in BMD determined only 16% of the anti-fracture effectiveness of BP. Markers of bone remodeling can be used as surrogate markers after 3 (bone resorption) or 6 (bone formation) months from the start of BP therapy. A decrease of 30% or more is considered to be prognostically effective for both antifracture and BMD gain. There is a direct relationship between the degree of bone remodeling markers decrease and the antifracture effectiveness of BP therapy. The decrease in markers persists throughout the entire period of therapy and, accordingly, they can be used as surrogate markers of effectiveness and adherence to BP therapy throughout the entire treatment period. However, the presence of pathological fractures is a key clinical manifestation of osteoporosis and should be considered first in every decision making compared to any surrogate marker.Thus, when prescribing BP treatment, surrogate markers of changes in BMD and/or markers of bone remodeling can be used to monitor the effectiveness of treatment throughout the entire period of treatment and patients’ monitoring.