Glucose homeostasis and safety in patients with acromegaly converted from long-acting octreotide to pegvisomant.

In clinical practice, patients with acromegaly may be switched from therapy with long-acting somatostatin analogs to pegvisomant. The effect of changing therapies on glucose homeostasis and safety has not been reported. The objectives of this study were to monitor changes in IGF-I levels, glycemic control, and safety, particularly liver function and tumor size. This was a multicenter, open-label, 32-wk trial study. The study was performed at outpatient clinics. Fifty-three patients with acromegaly previously treated with octreotide long-acting release (LAR) participated in this study. Pegvisomant (10 mg/d) was initiated 4 wk after the last dose of octreotide LAR and was adjusted based on serum IGF-I concentrations at wk 12, 20, and 28. The main outcome measures were changes in IGF-I, glycosylated hemoglobin A1c (HbA1c), fasting plasma glucose, and safety during the first 12 wk after conversion. At the end of pegvisomant treatment, IGF-I was normalized in 78% of patients. At wk 32, median fasting glucose concentration and HbA1c were reduced (-1.4 mmol/liter and -0.4%, respectively; both P < or = 0.0001) in the study population. Improvements in glycemic control occurred in patients with normal IGF-I concentrations at wk 4 [n = 15; fasting glucose, -1.7 mmol/liter (P < or = 0.0001); HbA1c -0.2% (P = 0.03)]. Decreases in fasting glucose and HbA1c levels were observed in patients with and without diabetes. HbA1c was reduced by more than 1.0% in patients with diabetes. Median pituitary tumor volume did not change, although tumor volume increased in two patients with macroadenomas. Conversion from octreotide LAR to pegvisomant was safe and well tolerated. Improved glycemic control indicates that pegvisomant should be considered in patients with acromegaly and diabetes.