Pharmacokinetic studies of human urinary kininogenase in healthy volunteers and animals

Plasma concentrations of human urinary kininogenase (HUK) were determined in healthy volunteers during and after intravenous (iv) infusion by enzyme immunoassay (EIA). Plasma kinin concentrations were also determined by radioimmunoassay (RIA), and related to HUK concentrations. When HUK was infused [at 0.04, 0.075, 0.15, and 0.3 p-nitroaniline unit (PNAU)/body] over 30 min, plasma HUK concentration rapidly increased and reached a maximum at the end of dosing. Then, the concentration of HUK in plasma decreased biexponentially, and the elimination half-life of the terminal phase was found to be ∼170 min. The area under the curve of concentration versus time from 0 to 180 min (AUC0–180min) and the maximum concentration (Cmax) increased in proportion to the dose, whereas the pharmacokinetic parameters [mean residense time (MRTinf) = 200–270 min, plasma clearance (CLp) = 2.5–3.3 mL/min/kg, volume of distribution at steady state (Vdss) = 470–730 mL/kg] did not vary significantly within the dose range of the present study. On the other hand, when HUK was infused (at 0.15 PNAU/body), plasma kinin concentrations reached ∼2 ng of bradykinin eq/mL 15 min after the onset of administration. This concentration was maintained during the dosing period, after which kinin was rapidly eliminated, and its concentration returned to baseline at 10 min after dose withdrawal. Plasma kinin concentrations at 15 to 30 min after the onset of dosing (at 0.075, 0.15, and 0.3 PNAU/body) increased in proportion to the dose. The pharmacokinetic parameters of HUK (MRTinf, CLp, Vdss) were compared with those of rats, rabbits, and dogs (log–log plots of body weight versus MRTinf, CLp, and Vdss). The Vdss value showed a good correlation (r = 0.996 for n = 4) with the body weight of respective animal species, the correlation with CLp was weak (r = 0.911), and MRTinf did not exhibit any correlation.