Oral versus intravenous administration of lysine: equal effectiveness in reduction of renal uptake of [111In-DTPA]octreotide.

UNLABELLED During tumor therapy with radiolabeled somatostatin analogs, the kidneys are dose limiting. Renal uptake in patients can effectively be reduced by a 4- to 10-h intravenous infusion of a lysine/arginine solution, thereby increasing the maximum radiation dose to the tumor without renal side effects. Oral administration of amino acids could facilitate this labor-intensive procedure. Therefore, the effects of oral versus intravenous administration of D-lysine were compared in rats injected with [111In-diethylenetriaminepentaacetic acid (DTPA)]octreotide. METHODS Rats were intravenously injected with 3 MBq/0.5 microg [111In-DTPA]octreotide and also received D-lysine intravenously or orally in various concentrations and following various time schedules. Twenty-four hours after injection, a biodistribution study and renal ex vivo autoradiography were performed. RESULTS Renal uptake was reduced significantly-up to 40%-in all lysine-treated groups, without affecting the uptake in other organs. CONCLUSION Renal uptake of this radiolabeled peptide can be reduced up to 40% both by oral and by intravenous administration of lysine in rats.