Comparison of the pharmacokinetics of porcine calcitonin in saline and in gelatin diluents in healthy volunteers.

A randomised 2-way crossover study was carried out in nine healthy male volunteers to compare the pharmacokinetics of porcine calcitonin (pCT) following i.m. administration of 160 i.u. of pCT in physiological saline or in a solution of hydrolysed gelatin. A new radioimmunoassay for pCT is described. It employs an antiserum raised in a guinea pig and a labelled tracer prepared from highly purified pCT. While comparable mean areas under the serum concentration-time curve for both dosage forms indicate equivalent bioavailability, the serum pCT profiles were different; peak pCT levels of 8.3 +/- 0.8 ng ml-1 (s.e.m.) occurred at 13 +/- 2 min (s.e.m.) with peak levels of 4.8 +/- 0.5 ng ml-1 (s.e.m.) when the gelatin diluent was used. The hypocalcaemic effects produced by the two preparations of pCT were of short duration (less than 1 h) and of a similar magnitude (-0.08 to -0.12 mmol.l-1). Comparable degrees of hypophosphataemia (-0.11 to -0.15 mmol.l-1) were observed 20 min post-injection. The administration of pCT in gelatin and saline diluents resulted in markedly different pharmacokinetic profiles. Whether there are therapeutic advantages in the use of either diluent remains to be investigated.