HEMOGLOBIN-BASED BLOOD SUBSTITUTES: FURTHER PRECLINICALS

HEMOGLOBIN-BASED BLOOD SUBSTITUTES: FURTHER PRECLINICALS and Phase I safety studies should be conducted before efficacy trials proceed, FDA's Blood Products Advisory Committee concluded in a March 15 draft "consensus statement." The draft document, which summarizes conclusions from the committee's March 14 closed session with companies at work on hemoglobin-derived red cell substitutes, recommends a number of specific preclinical and clinical studies to address unexplained toxicities seen in previous safety trials. The advisory committee's suggestions include in vitro product characterization tests, animal studies "in several species," including primates, and safety studies in healthy human volunteers. The committee suggested that the initial human safety studies begin at low doses (i.e., 250 mg/kg), with careful monitoring of circulatory and immune parameters, including complement/kinin/coagulation cascades, histamine release, and levels of thromboxane metabolites and leukotrienes. After establishing safety at low doses, the document proposes that studies at higher doses should continue in normal volunteers before firms begin efficacy testing. The document emphasizes that while the panel members remain "concerned about the intensity and severity of unexplained reactions in human recipients," they continue to support development of hemoglobin-based oxygen carriers. Toxicities from hemoglobin-derived blood substitutes pose a risk to the kidneys and liver, heart, lungs and vascular system, immune system, central nervous system, and reticuloendothelial system, according to the committee's statements. The committee also found that the source of observed toxic effects has not been determined conclusively, listing hemoglobin itself, its breakdown products such as heme, hemichrome, free iron and hemoglobin dimers, and manufacturing contaminants as potential sources of adverse effects. * Northfield Labs, of Evanston, Illinois, is among the companies that have been developing hemoglobin-derived red cell substitutes. The company said it is unclear how the committee's recommendations would affect the firm's Phase I testing program for its polymerized hemoglobin-product. According to FDA, no firms have progressed further than initial Phase I studies for such products.