Pharmacokinetics of repeated i.v. bolus administration of high doses of r-met-Hu interleukin-2 in advanced cancer patients.

We studied the pharmacokinetics of recombinant methionyl human interleukin-2 alanine (r-met-Hu IL-2 [ala 125]) given at high doses by i.v. bolus according to Rosenberg's initial schedule in seven patients with advanced cancer. Serum concentrations of IL-2 were measured by radio-immunoassay. The drug followed second-order kinetics. During the administration of repeated high doses of IL-2, we noted a progressive increase in the volume of distribution (from 5,984 +/- 1,850 to 9,084 +/- 4,345 ml) and a progressive decrease in the AUC (from 32,643 +/- 3,817 to 22,397 +/- 511 IU min ml-1) and beta-half-life (from 61 +/- 14 to 48 +/- 6 min); the peak serum IL-2 concentrations also decreased significantly. We attribute these findings to an expansion of the extracellular fluid space and an increase in the number of IL-2 target cells during the treatment.