The non-ionic surfactant Poloxamer 188 (RheothRx) increases plasma and whole blood viscosity

RheothRx injection is an intravenous formulation of Poloxamer 188, a non-ionic block copolymer surfactant which is actually used in clinical studies, e.g., during thrombolysis in acute myocardial infarction. We have analysed the influence of RheothRx on plasma and whole blood viscosity of healthy individuals in vitro. For that purpose plasma was incubated with 0, 0.75, 3.75 and 18.75 mg/ml RheothRx and whole blood with a constant hematocrit of 41.4% with 0, 0.4, 2 and 10 mg/ml RheothRx at 37 degrees C. Viscosity was measured with a Couette viscometer at shear rates of 94, 11, 0.9 and 0.1 s-1 as well as with a newly developed oscillating viscometer. In contrast to other studies, we found no favourable effect of RheothRx on plasma and whole blood viscosity. At the highest RheothRx concentration an increase in high and low shear viscosity was observed. Erythrocyte morphology remained unchanged. These data, although on normal blood in vitro, suggest that the positive effects of RheothRx in vivo may not be caused by improved flow properties of blood, but could rely on other mechanisms.