GH receptor blocker · acromegaly
A modified version of human growth hormone that blocks, rather than activates, the growth hormone receptor. It is made in genetically engineered E. coli bacteria and carries attached polyethylene glycol chains. It treats acromegaly, a condition in which a pituitary tumor makes too much growth hormone.
Growth hormone acts through receptors on cell surfaces; one major result is production of IGF-1, which runs high in acromegaly2. Pegvisomant is growth hormone with several amino acid substitutions plus attached polyethylene glycol1. It binds the growth hormone receptor without switching it on, blocking the body's own growth hormone from acting1. As a result, IGF-1 and other growth-hormone-responsive proteins, such as IGFBP-3 and the acid-labile subunit, fall1. Treatment is judged by IGF-1, the stated goal on its label, partly because the drug resembles growth hormone closely enough to cross-react in standard growth hormone blood tests, which makes those measurements unreliable during treatment1.
In a 12-week randomized, placebo-controlled trial of 112 people with acromegaly, IGF-1 became normal in 54% to 89% of those on three dose levels of pegvisomant versus 10% on placebo, with dose-related falls in IGF-1; at the two higher dose levels, ring size, soft-tissue swelling, excess sweating and fatigue also improved, and adverse-effect rates were similar across groups2. ACROSTUDY, a real-world, non-interventional study, followed 1,464 patients treated with pegvisomant alone for a median of six years. At the last observation, 62% had a normal IGF-1; on MRI, 7% showed an increase in pituitary tumor size; and treatment-related adverse events were uncommon, the most frequent being out-of-range IGF-1, fatty lumps at injection sites and raised liver enzymes. None of the 31 deaths were judged treatment-related3.
FDA-approved in March 2003 as Somavert for acromegaly when surgery or radiation has not worked well enough or is not appropriate; the goal of treatment is a normal IGF-1 level1. It is made by Pharmacia & Upjohn, a Pfizer subsidiary1.
Per the FDA label, the most common reactions are infection, pain, nausea, diarrhea, abnormal liver tests, flu-like illness and injection-site reactions. Warnings cover liver-enzyme elevations, so liver tests are checked before and during treatment; low blood sugar in people with diabetes as their insulin sensitivity improves; fat buildup at injection sites; and systemic allergic reactions. Because it cross-reacts with growth hormone assays, those blood tests are unreliable during treatment1.
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