What it is
Pegvisomant is growth hormone turned inside out — a copy that occupies the receptor without switching it on. Its label (section 11, effective 2025-12-18) describes it as "an analog of human growth hormone (GH) of recombinant DNA origin that acts as a GH receptor antagonist", containing 191 amino acid residues — the same length as somatropin, natural growth hormone — with nine amino acid substitutions and several polyethylene glycol (PEG) chains attached.
| From the Somavert label | |
|---|---|
| Protein chain | 191 residues, 22 kDa |
| Changes from growth hormone | 9 substitutions (e.g. Gly120Lys) |
| PEG | ~5 kDa chains at up to nine attachment sites |
| Whole molecule | predominantly ~42, 47 and 52 kDa |
| Made in | genetically modified E. coli |
At 191 residues it is a protein many times over — see the peptide-or-protein entry.
How it works
Growth hormone acts by bringing two receptor molecules together. A 2000 review by its clinical investigators (Parkinson and Trainer, PMID 10984267) describes pegvisomant as "designed to bind to the GHR at the cell surface and hence block this process", and calls blocking growth hormone's action, rather than its release, "a novel concept in the medical management of acromegaly". The older acromegaly drugs — octreotide and the other somatostatin analogues — work the other way, by reducing release.
Because growth hormone levels stay high, the label states that doses are adjusted on blood IGF-1, the hormone growth hormone drives, "not … based on growth hormone (GH) levels or signs or symptoms of acromegaly".
What the trials show
| Study | Patients | Result |
|---|---|---|
| Trainer et al., NEJM 2000 (PMID 10770982) — 12 weeks, randomised, double-blind | 112 | IGF-1 normal in 10% (placebo), 54% (10 mg/day), 81% (15 mg/day), 89% (20 mg/day); ring size, soft-tissue swelling, sweating and fatigue fell on the two higher doses |
| ACROSTUDY final monotherapy data, Pituitary 2026 (PMID 41984268) — real-world registry | 1,464, median 6.0 years | IGF-1 normal in 62.3% at last observation; serious adverse events in 19.3%; 31 deaths (2.1%), none judged treatment-related; tumour size increased on MRI in 7.2% |
The registry is observational and sponsored (two authors list the manufacturer as employer), and does not have a comparison group.
What the label says
- Indication: acromegaly in patients with an inadequate response to surgery or radiation, or for whom those are not appropriate; the goal is a normal IGF-1.
- Dosing as labelled: a 40 mg loading dose under clinical supervision, then daily injections in a labelled range of 10 to 30 mg, adjusted by the prescriber on IGF-1 measured every four to six weeks.
- Warnings: liver toxicity — liver tests before starting and during treatment; ALT/AST over ten times the upper limit in 2 patients (0.8%) before approval, and transient rises up to 15 times in under 2% across two open-label trials; low blood sugar in people with diabetes, as blocking growth hormone can improve insulin sensitivity; cross-reaction with growth hormone assays; lipohypertrophy at injection sites; systemic hypersensitivity.
Where it stands
- Approved in the US as SOMAVERT, BLA021106, on 2003-03-25 (openFDA Drugs@FDA, checked 2026-11-02).
- Research volume: PubMed holds 730 records for pegvisomant, 38 indexed as randomised trials; ClinicalTrials.gov lists 44 studies (searched 2026-11-02).
Related reading
GHRH is the hormone at the top of the same axis; pegvisomant is dosed against insulin-like growth factor 1, the signal further down.