Long-term treatment of acromegaly with pegvisomant, a growth hormone receptor antagonist

Background Pegvisomant is a new growth hormone receptor antagonist that improves symptoms and normalises insulinlike growth factor-1 (IGF-1) in a high proportion of patients with acromegaly treated for up to 12 weeks. We assessed the effects of pegvisomant in 160 patients with acromegaly treated for an average of 425 days. Methods Treatment efficacy was assessed by measuring changes in tumour volume by magnetic resonance imaging, and serum growth hormone and IGF-1 concentrations in 152 patients who received pegvisomant by daily subcutaneous injection for up to 18 months. The safety analysis included 160 patients some of whom received weekly injections and are excluded from the efficacy analysis. Findings Mean serum IGF-1 concentrations fell by at least 50%: 467 mug/L (SE 24), 526 mug/L (29), and 523 mug/L (40) in patients treated for 6, 12 and 18 months, respectively (p<0.001), whereas growth hormone increased by 12.5 g/L (2.1), 12.5 mug/L (3.0), and 14.2 mug/L (5.7) (p<0.001). Of the patients treated for 12 months or more, 87 of 90 (97%) achieved a normal serum IGF-1 concentration. In patients withdrawn from pegvisomant (n=45), serum growth hormone concentrations were 8.0 g/L (2.5) at baseline, rose to 15.2 mug/L (2.4) on drug, and fell back within 30 days of withdrawal to 8.3 mug/L (2.7). Antibodies to growth hormone were detected in 27 (16.9%) of patients, but no tachyphylaxis was seen. Serum insulin and glucose concentrations were significantly decreased (p<0.05). Two patients experienced progressive growth of their pituitary tumours, and two other patients had increased alanine and asparate aminotransferase concentrations requiring withdrawal from treatment. Mean pituitary tumour volume in 131 patients followed for a mean of 11.46 months (0.70) decreased by 0.033 cm(3) (0.057; p=0.353). Interpretation Pegvisomant is an effective medical treatment for acromegaly.