Role of calcitriol in the treatment of postmenopausal osteoporosis.

Treatment with 1,25-(OH)2D3 (calcitriol) was compared with placebo in a double-blind, randomized, parallel clinical trial of 24 months' duration. Subjects were white women with postmenopausal osteoporosis. The study was completed by 15 patients who received placebo and 12 patients who received calcitriol. Positive slopes were observed in the active treatment group for total body calcium, bone mineral content of the radius, bone mineral density of the lumbar spine, and radiographic absorptiometry of the middle phalanges. In contrast, negative slopes were observed for the bone mineral measurements in the placebo group. Measurement of urinary hydroxyproline and of serum alkaline phosphatase and osteocalcin suggested that the mechanism of action of 1,25-(OH)2D3 involved reduction of bone resorption. Hypercalciuria occurred regularly and preceded hypercalcemia by about 2 weeks. A decline in creatinine clearance was observed in two patients, one of whom had nephrolithiasis on sonography. Calcitriol is effective in preventing bone loss, but must be used with caution.