In contrast to human hemoglobin whose oxygen affinity relies on adequate levels of 2,3-bisphosphoglycerate, the affinity of bovine hemoglobin for oxygen is regulated by the concentration of chloride ions in the plasma. It has a dose-dependent intravascular half-life of 19 to 24 hours.
Hemopure and RBCs containing the same concentration of hemoglobin, have the same oxygen carrying capacity (1.39 mL O2/g Hb). A unit of packed red blood cells (pRBC) typically has a higher hemoglobin concentration (26-32 g/dl) than does Hemopure (13.1 g/dl) and, therefore, has a higher oxygen carrying capacity (= higher efficacy) than does Hemopure.
For this reason, and because units of pRBC (250-300 mL) and Hemopure (250 mL) may have different volumes, Hemopure should not be considered a unit-for-unit alternative to pRBC. Rather, the clinical need for oxygen carrying capacity and the total circulating hemoglobin concentration (RBC Hb + plasma Hb) should guide determination of Hemopure dose. Achieving a particular target total Hb concentration will require a larger number of Hemopure units than pRBC units.
Numerous in vivo and in vitro pharmacology and toxicology studies have been performed on Hemopure over a period of more than 15 years. These studies have defined the pharmacological and toxicological properties of Hemopure in a variety of animal models ranging from ischemia, hemorrhagic shock, and cardiac arrest and include the appropriate complement of toxicology studies.
Hemopure has been administered to more than 800 human subjects in 22 completed clinical trials, including red blood cell-controlled trials in elective surgical patients where the product was administered at doses up to 300 g (10 units). Hemopure eliminated or reduced the requirement for allogeneic blood transfusions. Results from two red blood cell-controlled trials in general and orthopedic surgery have been published and are listed in the literature.