General Information

Somavert is the first in a new class of medicines called growth hormone receptor antagonists and the only medicine designed to specifically block the effects of excess growth hormone in acromegaly.

Somavert (pegvisomant), an analog of human growth hormone, is an injectable medication that has been structurally altered to act as a growth hormone (GH) receptor antagonist. Over production of growth hormone leads to abnormally high insulin-like growth factors (IGF-I), which then cause acromegaly like symptoms.

Somavert is indicated for the treatment of acromegaly in patients who have had an inadequate response to surgery and/or radiation therapy and/or other medical therapies, or for whom these therapies are not appropriate. The goal of treatment is to normalize serum IGF-I levels.

Somavert is available in single-dose, sterile glass vials in 10, 15, or 20 mg strengths.

Clinical Results

FDA approval of Somavert was based on the data from a 12-week, randomized, double blind, placebo-controlled study enrolling 112 subjects with acromegaly previously treated with therapy. Results showed that after 12 weeks of treatment, serum IGF-I levels were normalized in 39%, 75%, and 82% of subjects treated with 10, 15, or 20 mg/day of Somavert, respectively, versus 10% of subjects treated with placebo. The three Somavert groups also showed dose-dependent reductions in serum levels of IGF-I and IGF binding proteins compared with placebo at all post-baseline visits.

Following withdrawal from previous medical therapy, the 80 patients randomized to treatment with Somavert received a subcutaneous (SC) loading dose, followed by 10, 15, or 20 mg/day SC. Each individual score (for soft-tissue swelling, arthralgia, headache, perspiration and fatigue) was based on a nine-point ordinal rating scale (0 = absent and 8 = severe and incapacitating), and the total score was derived from the sum of the individual scores.

In addition, subject's ring size at week 12 was smaller in the groups treated with Somavert (15 or 20 mg) of, compared with placebo. The mean total score for signs and symptoms at week 12 was lower in each of the groups treated with Somavert, compared with the group treated with placebo.

Mechanism of Action

Pegvisomant is a recombinant DNA protein containing 191 amino acid residues to which several polyethylene glycol (PEG) polymers are covalently bonded. It is synthesized by a specific strain of Escherichia coli bacteria that has been genetically modified by the addition of a plasmid that carries a gene for GH receptor antagonist. Pegvisomant selectively binds to growth hormone (GH) receptors on cell surfaces, where it blocks the binding of endogenous GH, and thus interferes with GH signal transduction. This inhibition of signal results in the decrease of insulin-like growth factor (IGF-I) and IGF binding proteins. High IGF-I levels lead to the numerous health complications associated with acromegaly.

Literature References

van der Lely AJ, Hutson RK, Trainer P, et al. Long-term treatment of acromegaly with pegvisomant, a growth hormone receptor antagonist. The Lancet 2001 ; 358: 1754-1759.

Molitch ME. Clinical manifestations of acromegaly. Endocrinol Metab Clin North Am. 1992;21:597-614.

Orme SM, McNally RJ, Cartwright RA, et al. Mortality and cancer incidence in acromegaly: a retrospective cohort study. United Kingdom Acromegaly Study Group. J Clin Endocrinol Metab. 1998;83:2730-2734.

Bates AS,Van't Hoff W, Jones JM, et al. An audit of outcome of treatment in acromegaly. Q J Med. 1993;86:293-299.

Ben-Shlomo A, Melmed S. Acromegaly. Endocrinol Metab Clin North Am. 2001;30:565-583.

Sheaves R. A history of acromegaly. Pituitary. 1999;2:7-28.