Bone Abstracts

Three oral bisphosphonates ibandronate, alendronate, and risedronate are commonly used for the treatment of osteoporosis but they have not previously been compared in the same study. Our aim was to identify determinants of change in bone turnover markers (BTM) in response to these bisphosphonates in a 2-year randomised parallel group trial. We recruited 171 postmenopausal osteoporotic women (<85 years) who were randomised to receive ibandronate (150 mg monthly), alendronate (70 mg weekly), or risedronate (35 mg weekly) plus daily calcium (1200 mg) and colecalciferol (800 IU). Ninety women returned at 2 years. The study had Local Research Ethics Committee approval. Fasting blood and urine samples were collected at baseline, 1, 2, 4, 12, 48, and 96 weeks. Biochemical measurements included: serum bone ALP, osteocalcin, PINP, CTX, PTH, and 25(OH)D (IDS-iSYS, Immunodiagnostic Systems, UK), urine NTX (Vitros ECi, OrthoClinical Diagnostics, UK). Mixed model statistical analysis was used to account for repeated measures and identify the determinants of percentage change in BTM. We evaluated the influence of baseline BTM, age, BMI, and BMD T-score stratum.

There was a significant difference between treatment groups for bone resorption markers (Table 1) with greater responses for alendronate and ibandronate than for risedronate.

Bone resorption markers were significantly decreased by week 1 (P<0.001), bone formation markers by week 4 (bone ALP, P=0.02, OC and PINP P<0.001). High baseline bone turnover was related to a greater decrease in BTM. BMI was associated with change in bone ALP and NTX (Table 1). Age and BMD stratum were not significant. Response to oral bisphosphonate is determined by the type of bisphosphonate, the baseline BTM and the BMI.