Pegvisomant (Somavert) is an injectable medication used in the treatment of uncontrolled acromegaly, where therapies used (which are very effective)have failed to meet the desired effect in some patients.
The PBS listing of this new treatment for acromegaly from the 1 st of September 2016 is welcomed news for patients with acromegaly.
Somavert works by blocking the action of growth hormone produced by the pituitary tumour. Somavert is a genetically engineered form of modified growth hormone that binds to the growth hormone receptor but not activating it. This occupancy prevents natural growth hormone from accessing and activating its receptor.
Octreotide, lanreotide and pasereotide, called aomatostatin analogues are the major drugs used to treat acromegaly. They work by inhibiting the secretion of growth hormone from the tumour. Somavert has no action on the pituitary tumour. Its action as a blocker therefore works very differently from somatostatin analogues.
Patients who are not adequately or cannot tolerate octreotide, lanretotide or pasereotide are eligible for Somavert treatment. An application by the treating doctor requires the completion of a PBS authority application form to the Department of Human Services. The PBS listing for Somavert will not apply if the patient is already receiving a PBS listed somatostatin analogue for acromegaly.
Somavert is administered as a single daily injection. The medication is available in three dosage strengths of 10, 15 and 20mg. The treatment dose is determined by monitoring the level of IGF-1 in blood. IGF-1 is a hormone produced by the body in response to the action of growth hormone. Growth hormone itself is not measured during treatment because Somavert is chemically similar to growth hormone such that standard laboratory methods cannot distinguish between the two.
Somavert has been used in Europe and in the United States for over 15 years. It has a good safety profile. The side effects are mainly from injection site reactions. The drug may affect the function of the liver in a small proportion of patients. This easily detected from routine blood tests and return to normal on stopping the medication. There is no evidence that Somavert effects the size or growth of the pituitary tumour.