Salmon calcitonin therapy for Paget's disease of bone. The problem of acquired clinical resistance.

During the initial months of long-term treatment of Paget's disease of bone with salmon calcitonin, circulating alkaline phosphatase activity and urinary hydroxyproproline excretion usually decrease by about 50%. In 22 of 85 patients these parameters returned to pretreatment levels despite continuous therapy. Nineteen patients who were resistant to salmon calcitonin had salmon calcitonin antibodies in high titer. Human calcitonin has been effective in suppressing disease activity in these patients. The pathogenesis of calcitonin resistance in patients without antibodies is unknown.