Effects of Prolonged Administration of Porcine Calcitonin in Postmenopausal Osteoporosis

The effect of the administration of homogeneous porcine calcitonin (PCT) was studied in five patients with postmenopausal osteoporosis. Two patients had complete metabolic studies for 1 month before and 1 month during treatment which began at 100 μg of PCT/day and progressively increased to a maximum of 500 μg/day (short-term studies). Three patients were studied before and after 3 to 4 months of home treatment with 200 μg of PCT/day. In the shortterm studies, there was no clear change in calcium or phosphorus balance, 47Ca kinetics, or urinary hydroxyproline excretion after treatment, while serum calcium and magnesium both showed a slight decrease. In the three long-term studies, serum calcium and magnesium concentrations diet not change as a result of treatment. Serum immunoreactive parathyroid hormone (IPTH) increased and the percentage tubular reabsorption of phosphate decreased in all patients. Bone resorption was unchanged in one short-term patient and was increased in the remaining four patients IPTH correlated positively (P < 0.01) with bone resorption. It was concluded that PCT was not therapeutically beneficial under the conditions of the study. The failure to observe the expected decrease in bone resorption after chronic administration of PCT may have resulted from the hypocalcemic effect of PCT and subsequent stimulation of PTH secretion.