INFLUENCE OF CONCENTRATION AND INJECTION VOLUME ON THE BIOAVAILABILITY OF SUBCUTANEOUS GROWTH-HORMONE - COMPARISON OF ADMINISTRATION BY ORDINARY SYRINGE AND BY INJECTION PEN

In order to study whether the bioavailability of subcutaneously injected growth hormone (GH) is dependent on the concentration/volume injected, the relative GH bioavailability was evaluated in 14 GH-deficient patients. In a cross-over study the patients received, in random order two separate subcutaneous GH injections (Norditropin(R)) 4 IU administered by means of an ordinary syringe (4 IU/ml) and an injection pen with cartridge (Nordiject 24(R)) (12 IU/ml). Blood samples were drawn over a 14 hr period and assayed for serum concentrations of GH and IGF-I. The mean value (+/- S.D.) of the relative absorption fraction (F(pen/sy)) was 1.09 +/- 0.39. Mean values of C(max) were 8.6 ng/ml +/- 4.8 and 8.3 ng/ml +/- 7.5 for syringe and pen respectively. Corresponding values for T(max) were 311 min. +/- 131 for syringe and 309 min. +/- 104 for pen. Although a considerable interindividual variation was seen, the relative absorption fraction did not differ significantly from 1 (2 P = 0.78). Further there was no significant difference in neither C(max) (2 P = 0.39) nor T(max) (2 P = 0.55). IGF-I serum profiles tended to be higher following syringe compared to pen injection (2 P = 0.054). On the basis of this study we conclude that in this dosage regimen, GH bioavailability following pen injection equals that of injection by syringe (i.e. no effect of a three fold increase/decrease in GH concentration/volume respectively).