Long-term effects of octreotide on markers of bone metabolism in acromegaly: Evidence of increased serum parathormone concentrations

The effects of octreotide on biochemical markers of bone turnover were evaluated in patients with active acromegaly. Serum GH, IGF-I and serum and urinary markers of bone metabolism were measured before and after 4 months of treatment in 27 patients (short-term treatment) and after 12 and 24 months of treatment in 15 patients (long-term treatment). In the short-term, octreotide significantly decreased the levels of serum GH, IGF-I, calcium, osteocalcin, carboxyterminal propeptide of type I collagen and alkaline phosphatase plus urinary excretion of calcium. Short-term treatment significantly increased serum parathormone levels (before treatment 30.1 ±9.57 and at 4 months 46.1 ±24.98 ng/L, p<0.001) and urinary excretion of phosphate; urinary excretion of hydroxyproline was unchanged. The same results were observed during long-term treatment, except that there was no significant difference of serum calcium and alkaline phosphatase levels before and after treatment. Parathormone concentrations were still higher at 24 months compared with those prior to treatment (before treatment 31.9±9.74 and at 24 months 44.9±21.18 ng/L, p<0.05). The changes of most bone markers during octreotide therapy can be explained by the decrease of serum GH and IGF-I concentrations. On the other hand, the rise of parathormone concentrations suggests that octreotide has ulterior and long-standing actions on calcium homeostasis: intestinal malabsorption of calcium due to the octreotide could contribute to this secondary hyperparathyroidism. The clinical consequences of these alterations of bone metabolism need to be further clarified.