Time course of GH and IGF-1 levels following withdrawal of long-acting octreotide in acromegaly.

AIM: Several studies have demonstrated the efficacy of octreotide LAR administered intramuscularly at 4-week intervals in the treatment of acromegaly. In contrast, few data are available on the time course of GH and IGF-1 plasma levels following octreotide LAR withdrawal. This prompted us to study these parameters for up to 20 weeks following drug withdrawal in a group of 18 acromegalic patients treated for one year. DESIGN AND PATIENTS: We studied 18 patients treated with octreotide LAR 10 mg (n = 2), 20 mg (n = 15) and 30 mg (n = 1) every 4 weeks for one year. GH (mean level during a 4-hour daily profile) and IGF-1 concentrations were measured at the end of treatment, just before the last injection (baseline) and then 15 +/- 2 weeks (first control) after the last injection. In patients with GH levels below 2.5 micrograms/L and/or normal IGF-1 at the first control, a second control was performed four to eight weeks later.
RESULTS: After one year of treatment with octreotide LAR, the mean plasma GH concentration was 1.91 +/- 1.25 micrograms/L (mean +/- SE) and the mean IGF-1 concentration was 440 +/- 251 micrograms/L. Among the 18 patients, 13 had mean plasma GH concentrations below 2.5 micrograms/L and seven could be considered as well-controlled (normal IGF1 and mean GH levels below 2.5 micrograms/L). After treatment withdrawal, the plasma GH concentration remained below 2.5 micrograms/L at the first and the second controls in 2 of the 13 (15%) patients with suppressed GH levels on baseline. Among the seven well-controlled patients on baseline (GH levels below 2.5 micrograms/L and normal IGF-1), one (15%) remained well-controlled, one (15%) kept GH levels below 2.5 micrograms/L but increased IGF-1 levels, and one (15%) kept normal IGF-1 levels but increased mean GH levels at the first control. This hormonal status remained unchanged at the second control in these 3 patients.
CONCLUSIONS: These results show long-lasting suppression of GH secretion after treatment withdrawal in some acromegalic patients treated for 12 months with octreotide LAR. The duration of GH suppression after treatment withdrawal is variable. Mean GH levels remained below 2.5 micrograms/L in 15% of our patients for up to 21 weeks following withdrawal of octreotide LAR. In practice, it may be preferable to wait several months after long-acting somatostatin analog withdrawal before reassessing hormone status. Owing this long-lasting effect, a dose reduction to 10 mg and/or a longer interval between injections could be considered for very good responders, as this would lead to considerable cost savings without affecting GH or IGF-1 control.