Adding Phosphorus to Osteoporosis Drug Treatment

Bone Sparing by Calcium Salts With and Without Extra Phosphorus

Osteoporosis causes bones to weaken and break more easily. Calcium and phosphorus are two minerals that are essential for normal bone formation. Unfortunately, calcium salts commonly prescribed in anti-osteoporosis treatment bind phosphorus from food and restrict phosphorus available for bone building. Teriparatide is a drug that reduces the risk of fractures by increasing bone thickness and strength. Vitamin D is also necessary for strong bones and teeth. The purpose of this study is to evaluate the bone-building effectiveness of two calcium supplements, one with a source of phosphorus and one without, in combination with teriparatide and vitamin D in women with osteoporosis.

Osteoporosis is the most common type of bone disease. Calcium supplements normally used in anti-osteoporosis treatment are calcium salts of carbonate or citrate; however, these salts bind phosphorus from food in the intestine and restrict phosphorus available for bone building. This study will evaluate the efficacy of adding calcium phosphate to a regimen of teriparatide and vitamin D in increasing bone mineral density in women with osteoporosis. It is hypothesized that the group taking the phosphate-containing calcium supplement will have greater gains in bone mineral density (BMD) during the course of the study than the group not receiving phosphate.

All participants will receive teriparatide and vitamin D during the course of the 12-month study. Participants will be randomly assigned to one of two groups. One group will receive calcium phosphate and the other will receive calcium carbonate. BMD will be measured at spine and hip at baseline and at 3, 6, and 12 months of treatment.

Inclusion Criteria:

• Bone mineral density (BMD) T-score less than -1.0
• One or more vertebral fractures
• Serum creatinine less than 1.3 mg/dL
• Serum phosphorus less than 3.6 mg/dL
• Daily phosphorus intake below NHANES-III median
• Body mass index (BMI) less than 30 kg/m2

Exclusion Criteria:

• Paget's disease or history of osteosarcoma
• Systemic corticosteroid therapy
• Hyperparathyroidism
• Recent history of kidney stone
• Anticonvulsant therapy known to alter vitamin D metabolism
• Radiation therapy to bone