Differential action of pamidronate on trabecular and cortical bone in women with involutional osteoporosis

Since osteoporotic fractures are mainly related to the diminution of the bone mineral density (BMD), the effect of pamidronate (3-amino-1-hydroxy-propylidene) 1,1-bisphosphonate on the BMD of the spine, proximal femur and radius shaft was evaluated in an initial cohort of 35 postmenopausal women with at least one vertebral fracture due to involutional osteoporosis. Pamidronate was given continuously during 18 months in a daily oral dose of 4.8 to 6.0 mg/kg supplemented with calcium (1 g/day). BMD--measured by dual photon absorptiometry--increased after one year 5.3 +/- 1.0% (P less than 0.001) in lumbar spine and 5.3 +/- 1.5% (P less than 0.001) over trochanter. However no significant changes were observed in the BMD of the femoral neck, Ward's triangle or in the cortical bone of the radius shaft measured by single photon absorptiometry. Pamidronate also decreased significantly urinary hydroxyproline-creatinine excretion after 6 months and thereafter maintained a plateau. After 18 months of treatment the diminution was 42.6 +/- 4.9% (P less than 0.001). The differing effects of pamidronate on the BMD of lumbar spine and proximal femur might be ascribed to dissimilarities between the proportions of trabecular and cortical bone in these. These results suggest that pamidronate may be prescribed to prevent fractures in cases of involutional osteoporosis with a significant decrease of BMD in lumbar spine and/or trochanter.