Evaluation of the optimum dose of growth hormone (GH) for restoring bone mass in adult-onset GH deficiency: results from two 12-month randomized studies.

OBJECTIVE: To establish the optimum GH dose for restoring bone mineral density (BMD) in adult-onset GH deficiency (GHDA). DESIGN: Two separate randomized, controlled clinical trials. PATIENTS: Fifty-eight adults aged 45.1 (20-64) years with severe GHDA were followed in two 12-month studies. In the first study, patients were randomized to placebo or GH 1.7 IU/m2/day and in the second study GH 0.5 IU/m2/day or 1.0 IU/m2/day. MEASUREMENTS: BMD of the spine, hip, forearm and whole body was measured at 0 and 12 months. Alkaline phosphatase (AP) and collagen markers serum C-terminal propeptide of type I collagen (PICP), type I collagen telopeptide (ICTP) and N-terminal propeptide of type III collagen (PIIINP) were measured at baseline and every 3 months. RESULTS: Biochemical markers of skeletal and soft tissue collagen increased significantly and remained elevated throughout the study period. BMD changes depended on site, dose and gender. In placebo-treated patients, spinal BMD declined by 2.5%. At the low and medium doses, BMD increased by 2.4 and 3.1%, respectively, while a nonsignificant 0.2% decrease was seen with high dose. Forearm BMD decreased by 4.9% (P < 0.05) with high-dose treatment but remained unchanged at lower doses. Males showed larger gains in BMD, but the dose-response relationship was similar in males and females. CONCLUSION: A GH dose of 0.5-1.0 IU/m2/day (4-9 micro g/kg/day) stimulated bone remodelling and increased BMD over 12 months in patients with severe GHDA, irrespective of gender. A higher dose (1.7 IU/m2/day congruent with 15 micro g/kg/day) was associated with initial declines in forearm and whole-body BMD.