Poor responses to a test dose of subcutaneous octreotide predict the need for adjuvant therapy to achieve 'safe' growth hormone levels.

OBJECTIVE: Somatostatin analogues are an established treatment in acromegaly. This study was designed to evaluate whether the acute serum growth hormone (GH) response to a test dose of octreotide in acromegaly predicts longer-term response to the drug at 3 years. DESIGN AND METHODS: In 23 patients, GH responses across 8 h to a subcutaneous test dose (50 microg) of octreotide were compared with GH levels after 3 years of therapy. The majority had pituitary surgery as primary therapy and at 3 years were receiving at least 600 microg octreotide daily subcutaneously or 20 mg LAR monthly intramuscularly.
RESULTS: Seven had a test day GH Nadir of 5 mU/l or less of whom 4 achieved GH < 5 mU/l at 3 years. Sixteen had a test day nadir GH of 10 mU/l or less and of these 8 achieved GH < 5 mU/l at 3 years. Seven of the 23 had a GH Nadir >10 mU/l and of these 3 had achieved GH <5 mU/l at 3 years. However all of these 3 had received external pituitary irradiation within 4 years of the 3 year assessment, as compared with 3 of the <5 mU/l nadir group and 5 of the <10 mU/l nadir group.
CONCLUSIONS: In patients on optimal long-term doses of octreotide for acromegaly, absence of a nadir GH <10 mU/l in the 8 h after a test dose was associated with failure to achieve GH levels associated with a normal life expectancy (5 mU/l or less) unless adjunctive external pituitary irradiation was given. As well as testing tolerability a test dose of octreotide may help in determining which patients should be offered early external pituitary irradiation or therapy with a GH receptor antagonist if surgery has failed to achieve 'safe' GH levels.