Octreotide
The original somatostatin analogue, approved since 1988 for acromegaly, carcinoid syndrome and VIPoma. Extensively characterised.
Growth Hormone
Pegvisomant
A modified growth hormone molecule that blocks its own receptor. Approved for acromegaly and the most reliably effective option for normalising IGF-1.
Overview
Growth hormone has to bind two copies of its receptor and bring them together to send a signal. Pegvisomant is growth hormone with one of its two binding surfaces mutated: it grabs the first receptor perfectly well but cannot recruit the second, so the receptor pair never forms and no signal is sent. Because it blocks the receptor rather than the pituitary, it lowers IGF-1 regardless of what the tumour is doing.
A recombinant hGH analogue with eight substitutions in binding site 1 that increase receptor affinity, plus a G120K substitution in binding site 2 that prevents functional receptor dimerisation. Pegylated at multiple sites to extend half-life and reduce immunogenicity. Blocks GHR signalling at the target tissue, lowering hepatic IGF-1 production. Serum GH rises during treatment because pituitary feedback is removed — GH is therefore not a useful monitoring parameter, and IGF-1 is titrated instead. Normalises IGF-1 in the large majority of patients in long-term surveillance data.
Research areas
AcromegalyGH receptor biologyIGF-1 regulation
Dosing reported in the literature
Every protocol below is reproduced from a published study or approved labelling, with its source named. These are records of what was studied — not recommendations, and not a suggestion that any of them is appropriate for any person.
| Protocol as reported | Source |
|---|---|
| 40 mg subcutaneous loading dose, then 10 mg daily, titrated by 5 mg increments every 4–6 weeks against IGF-1 | Approved product labelling |
| Daily doses of 10, 15 or 20 mg versus placebo over 12 weeks | Trainer et al., New England Journal of Medicine 2000 |
Trial status
Phase 3 completed; supported by the long-running ACROSTUDY post-marketing surveillance programme.
Reported safety signals
- Liver enzyme elevation occurs in a minority and requires periodic monitoring; rare cases of hepatitis have been reported.
- Tumour size must be monitored by imaging, since the drug does not act on the adenoma itself.
- Injection-site lipohypertrophy has been reported.
- Serum GH rises on treatment and cannot be used to judge control — IGF-1 is the monitoring parameter.
Common questions
Why does growth hormone go up on a growth hormone blocker?
Because the drug blocks the receptor in the liver rather than the pituitary. IGF-1 falls, the pituitary senses less negative feedback, and secretes more GH. That is expected — it is why IGF-1, not GH, is the number used to titrate the dose.
Primary sources
Medical disclaimer
This page is for informational and research purposes only. Nothing here constitutes medical advice. The compounds discussed are research chemicals. Consult a qualified clinician before starting any protocol.
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