There is increasing evidence that pamidronate and related compounds are effective in the prevention and treatment of osteoporosis. It is therefore of relevance to document the time course and mechanism of bis‐phosphonate action in this condition. To this end, the present study describes the biochemical responses to prophylactic treatment with oral pamidronate (APD, 150 mg/day) in 16 glucocorticoid‐treated patients and contrasts them with those in 19 steroid‐treated control subjects. Measurements were made over a period of 12 months.

The treated patients showed a fall in urine hydroxyproline excretion at 6 weeks associated with a reduction in serum ionized calcium concentration, a rise in serum 1,25‐(OH)₂D₃, and a nonsignificant rise in serum bone gla protein (BGP). In contrast to BGP, serum alkaline phosphatase activity declined at 6 weeks, falling further at 3 months. Between 3 and 12 months, BGP levels paralleled those of alkaline phosphatase and hydroxyproline, all these being significantly below their initial values, and the other parameters returned to baseline. There was a gradual increase in plasma phosphate concentrations in the treated group over the 12 month period.

It is concluded that pamidronate produces an acute and sustained inhibition of bone resorption followed by a more gradual reduction in bone formation. This transient dissociation results in a reduction in serum calcium, leading to a rise in serum 1,25‐(OH)₂D₃, which in turn stimulates BGP production. Thereafter, indices of bone turnover remain subnormal but serum calcium and 1,25‐(OH)₂D₃ return to baseline.