Effects of long-term administration of alfacalcidol on bone mass and bone metabolism in patients with primary osteoporosis--comparison with calcium preparations

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Long-term administration of active vitamin D3 can reduce the loss of bone mass and the incidence of fractures in Japanese whose intake of calcium (Ca) is low. In a crossover study, we examined the safety and efficacy of 1 alpha (OH)D3 and combination therapy with a Ca preparation. We measured bone mass, the incidence of fractures and bone metabolism in 33 elderly patients with a high risk of fracture (mean age: 77.5 %/- 7.8 (SD) years). Subjects were randomly assigned to receive calcium lactate alone for 12 months after 12 months of combination therapy with 1 alpha (OH)D3 (1 microgram/day) (A-C group, 17 patients) or to take calcium lactate alone for 12 months and then undergo 12 months of combination therapy with 1 alpha(OH)D3 (C-A group, 16 patients). These subjects were followed for 24 months. In the A-C group, the bone mineral density (BMD) of the lumbar spine (L2-4 BMD) measured 6 months after the start of 1 alpha (OH)D3 administration was 3% higher than the baseline value. In the C-A group, L2-4 BMD measured 6 months after the start of calcium lactate administration had decreased by approximately 2%. The rate of decrease was the same 12 months after the start of administration. The differences in L2-4 BMD between the two groups 6 and 12 months after the start of administration were significant (p = 0.023 and p = 0.005, respectively). In the A-C group, the mean BMD of the distal one-third radius measured 6 months after the start of administration had increased by 5%, but the increase was 1% when measured 12 months after the start of administration. In the C-A group, there were no such changes. The incidence of vertebral fracture during combination therapy with 1 alpha(OH) D3 and Ca preparations in the A-C group was significantly lower than that in the C-A group (chi square test, p < 0.05). The serum Ca level in the C-A group gradually increased, as measured 6 and 12 months after the start of combination therapy with 1 alpha(OH) D3 and Ca preparations, although these changes were within the reference range. There was no hypercalciuria. Serum intact parathyroid hormone levels had decreased from 26.5 +/- 11.3 pg/ml and 30.7 +/- 10.3 pg/ml to 19.8 +/- 9.7 pg/ml and 25.5 +/- 9.6 pg/ml in the A-C group and the C-A group, respectively, by 6 months after the start of administration. The rate of decrease was significantly higher in the A-C group (p = 0.004). These findings suggest that long-term administration of 1 alpha(OH)D3 is safe even when combined with administration of Ca preparations, and that this agent inhibits parathyroid function, and thus prevents loss of bone mass and reduces the incidence of vertebral fracture.