Studies for revealing a possible sensitization to hirudin after repeated intravenous injections in baboons.

The immunogenic potential of natural and recombinant hirudin was investigated using baboons. Animals received 4 intravenous hirudin injections of 1,000 antithrombin units/kg at certain times (day 1, 3, 8 and 42) and were checked for an immune response. None of the tests performed (in vitro histamine-release, ELISA for detection of humoral hirudin-specific IgG and IgM antibodies by indirect ELISA, direct skin test) revealed any kind of sensitization to hirudin. Urinary excretion of hirudin was not diminished by successive injections, if diuresis was within normal ranges. In summary, these results confirm previous observations indicating the weak antigenic potential of hirudin. Therefore, immune reactions to hirudin in man during therapeutic measures requiring several exposures to the inhibitor should not to be expected under normal circumstances.