Formation of antibodies to synthetic human calcitonin during treatment of Paget's disease.

Low-titre antibodies to synthetic human calcitonin (hCT) were detected in a 69-year-old woman suffering from Paget's disease who was treated for 16 months with hCT and the diphosphonate EHDP. Levels of antibody were highest between 10 and 18 months after commencement of therapy, slowly decreased after completion of treatment and were later no longer measurable. There was no immunological response to a single re-injection of hCT 14 months after discontinuation of therapy. Formation of antibodies to hCT in man is a very rare event, this being the first recorded case of an immune response to synthetic human calcitonin, whereas synthetic salmon calcitonin induces an immune response in a high percentage (up to 78%) of the patients treated with this hormone.