Instant blood mediated inflammatory reaction (IBMIR) occurs when islets are exposed to blood and manifests clinically as portal vein thrombosis and graft failure. The aim of this study was to determine the impact of recombinant human activated protein C (rhAPC) and platelet inhibition on IBMIR in order to develop a better targeted treatment for this condition. Five thousand human islet cell equivalents (IEQ) were mixed in a PVC loop system with 7 mL of ABO compatible human blood and incubated with rhAPC, either alone or in combination with tirofiban. Admixing human islets and blood caused rapid clot formation, consumption of platelets, leukocytes, fibrinogen, coagulation factors and raised d-dimers. Islets were encased in a fibrin and platelet clot heavily infiltrated with neutrophils. Tirofiban monotherapy was ineffective, whereas rhAPC monotherapy prevented IBMIR in a dose-dependent manner, preserving islet integrity while maintaining platelet and leukocyte counts, fibrinogen and coagulation factor levels, and reducing d-dimer formation. The combination of tirofiban and low-dose rhAPC inhibited IBMIR synergistically with an efficacy equal to high dose rhAPC. Tirofiban and rhAPC worked synergistically to preserve islets, suggesting that co-inhibition of the platelet and coagulation pathways’ contribution to thrombin generation is required for the optimal anti-IBMIR effect.