Lack of antibody formation during long-term subcutaneous treatment with the somatostatin analogue octreotide in acromegaly.

Serum samples from 13 patients with active acromegaly on long-term sc treatment with octreotide (SMS 201-995, 1-36 months, mean daily dose 285 micrograms) were taken 12 h after the injection of their regular evening doses. Octreotide assay was performed using 125I-Tyr-SMS and a polyclonal rabbit anti-serum. For assessment of antibody formation both serum coated charcoal adsorption (adsorption of free octreotide) and polyethylene glycol precipitation (precipitation of IgG complexes) were used. The mean binding percentage in the patients proved to be similar to that of 5 healthy volunteers (p greater than 0.10). No specific binding was detected, whatever method used. No correlation was found between the binding percentages and octreotide serum levels, duration of octreotide treatment or daily octreotide dose (p greater than 0.10). These results strongly suggest that clinically relevant endogenous antibody formation is not a frequent event during long-term sc treatment of acromegalic patients with octreotide.