Effective dosing of lipid A analogue E5564 in rats depends on the timing of treatment and the route of Escherichia coli infection

Background. E5564, a competitive lipid A antagonist, inhibits endotoxin-stimulated inflammation and is under study in patients with sepsis. Methods. We tested whether clinically relevant variables, including the timing of treatment and the route of infection, influenced the effective dosing of E5564 in Escherichia coli-challenged rats. Results. All E5564 doses (0.3, 1.0, 2.0, and 3.0 mg/kg intravascular bolus followed by 10% of the bolus dose infused hourly for 24 h) administered 1 h before intravascular E. coli challenge similarly reduced the risk of death. Delaying the start of E5564 to 1 or 3 h after intravascular E. coli challenge significantly reduced the beneficial effect of the doses tested. However, increasing the dose of E5564 reversed some loss of efficacy for delayed treatment (P = .004, for increasing benefit with increasing dose at 1 h). During intrabronchial or intraperitoneal (extravascular) E. coli challenge, the pattern of effective E5564 dosing was the inverse of that for intravascular E. coli challenge (P = .001, for the interaction)-lower doses of E5564 were beneficial and higher doses were not (0.03, 0.3, 1.0, 2.0, and 3.0 mg/kg bolus followed by infusion) (P = .05, for decreasing benefit with increasing dose at 1 h). Conclusion. These findings suggest that, for maximal clinical benefit, E5564 should be given early and that dosing should be adjusted upward for intravascular infection and downward for extravascular infection.