Non-linear accumulation of gentamicin in guinea-pig kidney

The dose dependence of gentamicin renal uptake in guinea-pigs was studied. The concentration of gentamicin in the kidneys was determined 2 h post administration. The plot of gentamicin concentration vs. dose over the range 0.3-48 mg/kg iv revealed nonlinearity of the uptake. As the delivery of gentamicin to proximal tubule cells apparently obeys first order kinetics, the nonlinear process should occur at the cellular uptake level.