Metabolic effects of amino acid solutions infused for renal protection during therapy with radiolabelled somatostatin analogues

Background. Infusion of amino acids (AAs) can reduce renal uptake of radiolabelled somatostatin analogues resulting in a lower kidney exposure during peptide radiotherapy of patients with neuroendocrine tumours. In this study, we investigated the metabolic effects related to the infusion of large amounts of amino acids in patients undergoing positron emission tomography (PET) studies with [Y-86]DOTA(0)-D-Phe(1)-Tyr (3)-octreotide. Methods. Twenty-four patients, in four consecutive groups of six, received a 4 h infusion of 120 g of mixed AAs and, in addition, either a 4 h infusion of 50 g of L-lysine (n = 6), a 10 h infusion of 240 g of mixed AAs (n = 6), a 4 h infusion of 50 g Of L-lysine + L-arginine (Lys-Arg; n = 6) or no infusion (control; n = 6) in randomly ordered crossover studies. A number of clinical and biochemical parameters in blood and urine were measured over 24 h, including calculation of creatinine clearance, tubular reabsorption of inorganic phosphate (TRP) and fractional urate excretion. Results. No clinical side effects occurred during the infusions except for nausea and vomiting under mixed AAs. Patients in the latter group showed an increase in serum urea, whereas patients receiving L-lySine showed an increase in serum potassium and chloride. Inorganic phosphate levels dropped at 2.5 h in all groups except controls, and a significant decrease in TRP was observed with mixed AAs but not with L-lysine or Lys-Arg. Conclusion. Although infusion of AA solutions can improve the effect of therapy by allowing the administration of higher doses of radiolabelled somatostatin analogues, each preparation has specific sides effects that should be taken into account with this type of therapy.