Several clinical studies reported the efficacy of the long-acting SRIH analog, octreotide (Octreotide, Sandoz) in the treatment of acromegaly. Recently, another SRIH analog (BIM 23014, Ipsen Biotech) was shown to decrease plasma GH levels in acromegalic patients. The recent availability of a long-acting formulation of BIM 23014 [slow release (SR) lanreotide] could avoid the inconveniences associated with either repeated sc injections or continuous sc infusions. In this study, we compared the clinical and biochemical efficacies of both drugs in a cohort of 19 acromegalic patients, considered initially as responsive to octreotide and sequentially treated with octreotide (3 sc injections of 100-200 micrograms/day) for 12 months and with SR lanreotide (30 mg, im, every 10 or 14 days) for 6 months. Before octreotide treatment, baseline plasma GH (mean +/- SE of 8 hourly samplings) was 29.0 +/- 10.0 micrograms/L and was lowered to 3.2 +/- .2 micrograms/L during the first 7 h after the first 100-micrograms sc octreotide administration. After 12 months of treatment with octreotide, 14 of 19 patients (74%) were considered normalized, as their mean individual GH profiles and insulin-like growth factor-I (IGF-I) values were within the normal range. After octreotide withdrawal for 1 week, plasma GH and IGF-I levels rose to 18.3 +/- 4.8 and 4.1 +/- 0.4 U/mL, respectively. The first 30-mg SR lanreotide im injection produced an acute suppression of plasma GH levels (mean GH value during the 7 h after the injection, 3.0 +/- 0.4 micrograms/L), not different from results previously observed after the first octreotide injection. After 3 months of treatment with 30 mg SR lanreotide every 14 days, normalization of baseline GH and IGF1 levels was achieved in 6 of 19 patients. Ten patients, who did not achieve normal GH levels, subsequently received a 30-mg SR lanreotide injection every 10 days. Among them, normalization of GH and IGF-I levels occurred in 7 of 10 patients after 3 months of such a regimen. After 6 months of SR lanreotide treatment, 13 of 19 patients (68%) were considered normalized, with mean GH and IGF-I values, respectively, of 3.1 +/- 0.4 micrograms/L and 1.5 +/- 0.1 U/mL. The overall tolerance of both drugs (glucose homeostasis and gallstone formation) was similar.(ABSTRACT TRUNCATED AT 400 WORDS)