Phamacokinetics of Sustained-release Formulation of Growth Hormone in Experimental Animal

Kim, Myung jin; Kim, Sun Jin; Kim, Duk Hee; Chung, So Chung

Abstract

PURPOSE
Growth hormone(GH) therapy is very effective for the treatment of short stature, but it is unconvenient that GH should be injected daily because of short half-life. Sustained-release forms of GH preparation is needed for better compliance. This study aimed to measure peak pattern and duration of release of hGH from solid microparticles using sodium hyaluronate.
METHODS
In group 1, hGH(EutropinTM) 285microg/kg was injected subcutaneously to 2 Jindo dogs everyday for 7 days. In group 2, hGH solution(EutropinTM) was continuously infused subcutaneously for 12 hours a day for the first 2 days via mini pump(minimed co.) and then for 24 hours a day thereafter until 7th day with the rate of 11.9microg/kg/hr. In group 3, dose of 2mg/kg hGH in sustained-release formulation using sodium hyaluronate, was injected subcutaneously to 3 Jindo dogs. In group 4, two dose levels of 1mg/kg and 2mg/kg hGH in sustained-release formulation using sodium hyaluronate, were injected subcutaneously to each group of 4 Beagle dogs. To evaluate side reactions from continuous injection of sodium hyaluronate, sustained release form of hGH 2mg/kg was injected to 4 Beagle dogs once a week for 4 weeks and compared to 4 control Beagle dogs. Blood samples were withdrawn half- hourly for 6 hour and 2-4 times a day thereafter in Jindo dogs and at 6hr, 12hr, 22hr in the first day and twice a day(at 9:00, 16:00 O'clock) for the following 6 days.
RESULTS
In group 1, peak GH conc. of 122+/-27ng/ml was observed at 1 hour after hGH(EutropinTM) 285microg/kg injection and 1/2 of peak GH conc. at 4 hour. and decreased to 2ng/ml at 24 hour. GH AUC(Area under curve) was 670(ng/ml.hr). In group 2, initial steady state GH conc. of 25ng/ml occurred after 6 hour, however, GH conc. decreased gradually to 16ng/ml at the 7th day. GH AUC based on th initial steady state GH conc. was 600(ng/ml.hr). In group 3(Jindo dogs), GH conc. was peaked at 12 hour and 1/2 of peak GH conc at 30-46 hour and decreased to baseline at 70 hour. GH AUC was 2173(ng/ml.hr). In group 4(Beagle dog), peak GH concentrations of 56+/-7ng/ml and 108+/-12ng/ml were observed at 12 hour for the doses of 1mg/ kg and 2mg/kg, respectively and 1/2 of peak GH conc at 48 hour and decreased to baseline at 80 hour. GH AUC was 3560(ng/ml.h) for 2mg/kg treated dogs. Serum IGF-1 was increased to peak levels of 520ng/ml, and 580ng/ml for the doses of 1mg/kg 2mg/kg, respectively, and persisted above the baseline till 120 hour. There was no specific side reaction during experimental period.
CONCLUSION
Sustained-release form of hGH with sodium hyaluronate released GH for 70-80 hour with the peak level lower than that resulted from the conventional aqueous formulation of the equivalent dose, and higher concentration IGF-I maintained for 120 hour after injection above baseline. More extensive study is needed to permit for new therapeutic application.