Pegvisomant (Somavert)

Pegvisomant is a genetically engineered human-GH analog attached to polyethylene glycol. Developed from the mutated GH molecule B2036 and marketed as Somavert, it was US-approved in 2003. Unlike somatostatin analogs that reduce pituitary output, it blocks hormone action at the target receptor.

Engineered substitutions allow receptor binding without the conformational signaling normally produced by GH receptor subunit pairing. Hepatic IGF-1 production falls, improving the IGF-1-driven disease activity of acromegaly.

Pituitary GH production is not reduced, so measured GH can rise while IGF-1 normalizes. PEG prolongs exposure for daily dosing. In a controlled study, approximately 90% of patients receiving 20 mg daily normalized IGF-1, with symptom improvement. That trial result does not remove the need for individualized titration.

FDA approved pegvisomant in 2003 for acromegaly insufficiently controlled by surgery, radiation or other medical therapy, or when those options are unsuitable. Daily subcutaneous treatment usually follows a loading dose and is titrated to IGF-1.

Because IGF-1 reduction does not itself shrink the pituitary tumor, periodic imaging is used to monitor tumor size.

Common effects include injection-site reactions or lipohypertrophy, infections such as cold symptoms, pain, nausea, diarrhea, flu-like symptoms and abnormal liver tests. Elevated enzymes and rare liver injury require liver monitoring.

Patients with diabetes may develop lower glucose and need adjustment of their other medicines. Ongoing tumor surveillance remains important even when IGF-1 is controlled.