In vitro effects of aprotinin on activated clotting time measured with different activators

The effects in vitro of aprotinin on the activated clotting time measured with both celite- and kaolin-activated tubes were investigated in 21 consecutive patients requiring cardiopulmonary bypass. Four whole-blood samples (2 ml per sample) from each patient were tested simultaneously with Hemochron automated timing systems (International Technidyne Corp., Edison, N.J.) before, during, and after cardiopulmonary bypass. One tenth milliliter of either aprotinin (at a final concentration of 80, 120, or 180 KIU/ml) or saline solution was mixed in vitro with blood samples before determination of the activated clotting time. Aprotinin had no inhibitory effect on the activated clotting times of unheparinized blood. After heparin administration, aprotinin in the above concentrations prolonged the activated clotting times measured with celite-activated tubes by 47% to 71%, as compared with the measurements of the activated clotting time without the addition of aprotinin. The activated clotting times in kaolin-activated tubes were not increased, however, by the in vitro addition of aprotinin. Our in vitro results indicate that aprotinin in concentrations from 80 to 180 KIU/ml does not significantly enhance the inhibitory effects of heparin on the intrinsic coagulation system as evaluated by measurement of the activated clotting times in kaolin-activated tubes. The anticoagulation effect of heparin in patients receiving aprotinin infusion should be monitored with kaolin-activated instead of celite-activated tubes because the celite makes the measured activated clotting time unreliable in patients receiving aprotinin therapy. These in vitro results require confirmation in vivo in patients receiving aprotinin therapy.