Kinetics and haematological effects of erythropoietin in horses

A plasma kinetic study of erythropoietin (EPO) was carried out in 4 horses after subcutaneous administration (30 IU/kg bwt) of recombinant human erythropoietin (rhEPO). At standardized intervals for 48 h before injection and for 60 h post-administration, the EPO plasma levels were determined with an immunoradiometric assay based on a sandwich technique. The peak plasma concentration (30-113 mIU/ml) was observed after a delay ranging from 6 to 9 h post-administration and the drug levels reached a physiological value around 60 h following rhEPO injection. Moreover, reference values for plasma EPO concentrations, which were separately determined in 70 racehorses and 34 sport equines, ranged between 0 and 9 mlU/ml. After drug administration, no significant variations in red blood cell count, haemoglobin concentration, haematocrit or mean red blood cell volume were observed in the 4 animals. Further, minimal variations in these parameters were detected in a horse which received three 120 IU rhEPO/kg bwt doses successively. Therefore, high rhEPO doses are probably required to induce a visible haematological effect in equine species.