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Growth Hormone Receptor Antagonist Pregnancy: Contraindicated — insufficient data; theoretical fetal GH axis disruption. Effective contraception required during treatment.

Pegvisomant

Brand names: Somavert

Adult dose

Dose: Loading dose: 80mg SC (administered by healthcare professional). Maintenance: 10mg SC OD initially; adjust by 5mg increments every 4–6 weeks based on IGF-1 levels; usual dose 10–30mg OD.
Route: Subcutaneous injection
Frequency: Once daily (maintenance)
Max: 30mg OD (higher doses used in specialist centres with monitoring)
Mechanism: pegylated GH receptor antagonist — blocks GH signalling at receptor level, reducing IGF-1 production. Does NOT reduce GH levels (serum GH rises on treatment — do not use GH as monitoring parameter; use IGF-1 only). Used when somatostatin analogues (octreotide, lanreotide) fail to normalise IGF-1 or not tolerated.

Paediatric dose

Route: Subcutaneous injection
Frequency: Once daily
Max: Individualised
Not licensed in children. Seek specialist paediatric endocrinology opinion.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Hepatotoxicity risk — contraindicated if baseline LFTs >3× ULN. Monitor liver function closely.

Clinical pearls

  • CRITICAL monitoring point: serum GH rises on pegvisomant (GH receptor blocked — negative feedback lost) — monitor efficacy using IGF-1 ONLY, not GH
  • Hepatotoxicity: check LFTs at baseline; monthly for first 6 months; then every 6 months — stop if LFTs >5× ULN
  • MRI pituitary: annual surveillance — pituitary tumour may grow as GH rises (not blocked by pegvisomant); combination with somatostatin analogue may be used
  • Most effective IGF-1 normalisation of all acromegaly treatments (~90% response rate) — reserved for somatostatin analogue failures or intolerance

Contraindications

  • Hypersensitivity to pegvisomant or polyethylene glycol (PEG)
  • Hepatic impairment with LFTs >3× ULN at baseline

Side effects

  • Hepatotoxicity (elevated LFTs — important; monitor closely)
  • Injection site reactions
  • Headache
  • Fatigue
  • Arthralgia
  • Tumour growth (GH levels rise — monitor pituitary tumour size with MRI; no evidence of clinical tumour progression but theoretically possible)
  • Hypoglycaemia (if patient also on insulin — GH antagonism improves insulin sensitivity)

Interactions

  • Insulin, antidiabetic drugs — pegvisomant improves insulin sensitivity; reduce antidiabetic doses to avoid hypoglycaemia
  • Opioids — may interfere with GH secretion and response

Monitoring

  • IGF-1 (every 4–6 weeks during titration, then 6 monthly)
  • LFTs (monthly × 6 months, then every 6 months)
  • MRI pituitary (annually)
  • Blood glucose (improved insulin sensitivity)

Reference: BNFc; BNF 90; Endocrine Society Acromegaly Guidelines 2014; ACROSTUDY Registry. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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