Growth Hormone Receptor Antagonist Pregnancy: Not recommended during pregnancy or in women of childbearing potential not using contraception — limited human data and insufficient animal reproductive toxicity data. If used during pregnancy, IGF-I levels should be closely monitored, especially in the first trimester, and the dose may need adjusting. Should not be used in breast-feeding women; breast-feeding may be continued if the medicine is discontinued.

Pegvisomant

Brand names: Somavert

Pegvisomant is a pegylated growth hormone receptor antagonist used to treat acromegaly in patients with an inadequate response to surgery, radiotherapy or somatostatin analogues.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Loading dose 80 mg administered subcutaneously under medical supervision, followed by 10 mg once daily (reconstituted in 1 mL of solvent)

Route: Subcutaneous injection

Frequency: Single loading dose, then once daily

Max: 30 mg/day

LOADING DOSE DISCREPANCY — the UK SPC (SOMAVERT, used above) states an 80 mg loading dose, while the US prescribing information in the same bundle states a 40 mg loading dose followed by 10 mg daily from the next day. Clinician to confirm against the current UK SPC before this figure is published. Treatment should be initiated under the supervision of a physician experienced in the treatment of acromegaly. Dose adjustment: based on serum IGF-I levels, which should be measured every four to six weeks, with adjustments in increments of 5 mg/day to maintain serum IGF-I within the age-adjusted normal range and an optimal therapeutic response (the US label specifies increases of 5 mg every 4-6 weeks if IGF-I is elevated and decreases of 5 mg every 4-6 weeks if IGF-I is below normal; the dosage should not be based on growth hormone levels or on signs and symptoms of acromegaly). Available strengths: 10 mg, 15 mg, 20 mg, 25 mg and 30 mg. Before starting, assess baseline liver tests (serum ALT, AST, total bilirubin and alkaline phosphatase): if normal, treatment may proceed with ALT/AST monitored every 4-6 weeks for the first 6 months or at any time if symptoms suggest hepatitis; if elevated but 3 times ULN or less, treatment may proceed with monthly monitoring for at least 1 year then bi-annually for the next year; if greater than 3 times ULN, do not treat until a comprehensive workup establishes the cause of liver dysfunction. Administration: rotate the injection site daily to help prevent lipohypertrophy. Elderly: no dose adjustment required. Hepatic or renal impairment: safety and efficacy have not been established. Paediatric: safety and efficacy in children aged 0 to 17 years have not been established; no data available.

Dose adjustments

Renal

The safety and efficacy of pegvisomant in patients with renal (or hepatic) insufficiency have not been established; no dose adjustment is stated.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients

Side effects

Headache (25%, very common)
Arthralgia (16%, very common)
Diarrhoea (13%, very common)
Abnormal liver function tests, e.g. transaminase elevation (common)
Injection site reactions including injection site hypersensitivity, bruising/bleeding and injection site hypertrophy (lipohypertrophy) (common)
Influenza-like illness, fatigue, asthenia, pyrexia (common); hyperglycaemia or hypoglycaemia and weight increased (common)

Interactions

Insulin and/or oral hypoglycaemic agents — patients with acromegaly and diabetes mellitus may require careful monitoring and dose reductions of insulin and/or oral hypoglycaemic agents after starting pegvisomant, as glucose tolerance may improve
Opioids — in clinical studies, patients taking opioids often needed higher pegvisomant doses to normalise IGF-1 concentrations; the mechanism is not known
(NOTE: eMC §4.5 was not captured in the bundle; the above are from section 7 of the US prescribing information in the same bundle)

Clinical monograph

How it works

It binds to growth hormone receptors and blocks their functional dimerisation, preventing growth hormone signalling and thereby reducing hepatic production of insulin-like growth factor 1 (IGF-1).

Prescribing in practice

Hepatic enzymes can rise during treatment, occasionally markedly, so liver function must be monitored and significant or symptomatic derangement investigated.
Because it blocks the growth hormone receptor rather than lowering growth hormone, treatment is titrated to IGF-1 rather than growth hormone levels.
It does not control tumour size, so pituitary tumour growth should continue to be monitored by imaging.

Monitoring

Monitor serum IGF-1 to guide dosing and check liver function tests regularly throughout treatment.

Counselling the patient

Treatment success is judged by IGF-1 blood levels rather than growth hormone.
Report jaundice, dark urine or persistent nausea, which may signal liver problems.
Rotate injection sites to reduce the risk of fatty lumps developing at the site.

Evidence & guidelines

Normalisation of IGF-1 with pegvisomant in acromegaly is supported by the SPC and pivotal clinical trial data.

Reference: Endocrine Society Acromegaly Guidelines 2014; ACROSTUDY Registry; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways