Do different heparin brands influence activated clotting times?

A change in brand suppliers of heparin at our institution resulted in a number of anecdotal reports of possible differences in potency. Both products are marketed as heparin sodium extracted from porcine intestinal mucosa. Heparin Leo is 1000 international units (British Pharmacopeia) per ml. while Hepalean is 10,000 United States Pharmacopeia (U.S.P) units per ml. Perfusion records were retrospectively reviewed for one month periods when Heparin Leo (n = 52) or Hepalean (n = 61) were used to provide anticoagulation therapy for cardiopulmonary bypass. Heparin Leo was found to be less clinically potent than Hepalean. While increasing the initial loading dose of Heparin Leo by 5% (378 vs 398 units/kg-1), the initial post load activated clotting time (ACT) was 17% lower (556 vs 666 seconds). Heparin units required per kilogram per minute of cardiopulmonary bypass were 23% higher for Heparin Leo. Additionally 8 of 52 Heparin Leo patients did not achieve an initial post load ACT of greater than 400 secs while this occurred in 2 of 61 patients treated with Hepalean. These results were statistically significant. British Pharmacopeia and United States Pharmacopeia heparin reference standards differences are insufficient to explain the discrepancies observed in this study.