Pegvisomant
Growth hormone receptor antagonists
Growth hormone receptor antagonists
An engineered form of growth hormone that blocks its receptor. Given under the skin, it brings IGF-1 back to normal in acromegaly.
Quick facts
- Group
- Growth hormone receptor antagonists
- Target
- Growth hormone receptor (GHR)
- Key effects
- Injection-site reactions · Headache · Infections
- Monitor
- IGF-1 to adjust treatment
- ATC
- H01AX01
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows natural human growth hormone bound to the extracellular part of its receptor. Pegvisomant is a modified growth hormone that occupies the same receptor but cannot switch it on.
Pegvisomant is human growth hormone with amino acid substitutions and attached polyethylene glycol (PEG) chains. The substitutions disrupt the second receptor-binding site, so it binds the GH receptor and causes its internalisation but cannot produce the conformational change that starts JAK-STAT signalling. IGF-1 production falls. PEG slows clearance, so the drug lasts much longer than natural GH. It does not reduce GH secretion by the tumour.
- Pegvisomant binds the GH receptor on liver and other cells
- Its altered second site cannot activate the receptor
- JAK-STAT signalling and IGF-1 production fall
- GH from the tumour keeps circulating but has no effect
Indications
- Acromegaly with an inadequate response to surgery, radiotherapy or other drugs, alone or added to a somatostatin analogue Acromegaly and gigantism →
Adverse effects
Common
- Injection-site reactions
- Headache
- Infections (such as upper respiratory infections)
- Fatty lumps at injection sites (lipohypertrophy)
Contraindications
- Hypersensitivity to pegvisomant or its components
- Caution: unexplained raised liver transaminases before starting
Key interactions
- Somatostatin analogues (octreotide, lanreotide)
- Intended combination: added when IGF-1 stays high on the analogue alone
What is monitored
- IGF-1 to adjust treatment
- Liver function tests before and during treatment
- Pituitary MRI for tumour size
- Injection sites for lipohypertrophy
Administration and safety
- Subcutaneous injection; sites are rotated to limit lipohypertrophy
- Laboratory GH values are not used to judge response; IGF-1 is
- Prescribed by specialists after surgery, radiotherapy or other drugs have not controlled acromegaly
Pregnancy and breastfeeding
Information in pregnancy is limited; it is used only if the benefit justifies it.
Nursing care
- Check liver tests before the first dose and at follow-up
- Teach injection technique and site rotation; look for lumps at sites
- Ask about headache or visual changes that could suggest tumour growth
- Ask about jaundice, dark urine or right upper abdominal pain
Pharmacokinetics
- Absorption
- Given by subcutaneous injection; peak levels are reached days after a dose
- Elimination
- PEG chains reduce clearance
- Half-life
- About six days
Test yourself
Think of the answer, then tap the question to see it.
Why does GH not fall during pegvisomant treatment?
Pegvisomant blocks the GH receptor; it does not act on the pituitary tumour, and loss of IGF-1 feedback can even increase GH secretion.
What is the role of PEG in pegvisomant?
The attached polyethylene glycol chains reduce clearance, giving a half-life of about six days instead of minutes.
Which laboratory test is checked for safety before and during pegvisomant?
Liver function tests, because raised liver enzymes are its main laboratory adverse effect.
Which marker shows that acromegaly is controlled on pegvisomant?
A normal IGF-1 level.
Connections
← Back to the class: Growth hormone receptor antagonists
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Pegvisomant for acromegaly (Australian Prescriber (PubMed Central), 2017); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.