Establishment of the second international standards for porcine and human calcitonins: report of the international collaborative study.

The biological potency of calcitonins in clinical use in long-term treatment of Paget's disease of bone and, increasingly, in osteoporosis is usually expressed international units defined by the relevant World Health Organization international reference preparation. The international reference preparations for porcine and human calcitonins were ampouled in 1970 and stocks are now exhausted. Replacement standards were ampouled in 1989 and have been evaluated and calibrated by an international collaborative study comprising 16 laboratories in 12 countries. Evaluations included high-performance liquid chromatography and in vitro bioassay; calibration of each new ampouled preparation in terms of its international reference preparation was by in vivo rat hypocalcaemia bioassay. On the basis of the results of the study and with the agreement of the participants, replacement standards were established by the Expert Committee on Biological Standardization of the World Health Organization in 1991: the international standard for porcine calcitonin (ampoule code 89/540), with an assigned potency of 0.8 international units per ampoule, and the international standard for human calcitonin, with an assigned potency of 17.5 international units per ampoule. Both international standards appeared to be sufficiently stable to serve as the international standards for in vivo biological assays. Comparison of the two species of calcitonin in the same hypocalcaemia assay showed that they were approximately equipotent when the doses were given intravenously but that the human peptide was four- to sixfold more potent than porcine calcitonin when doses were given subcutaneously, emphasizing the need to compare "like with like".