Romiplostim (Nplate)

A synthetic 20-amino acid peptide that acts as a direct thrombin inhibitor by binding both the catalytic active site and anion-binding exosite 1 of thrombin. Bivalirudin inhibits both free and clot-bound thrombin, providing more predictable anticoagulation than heparin without requiring antithrombin III as a cofactor. It is enzymatically cleaved by thrombin itself, producing a self-limiting anticoagulant effect with a 25-minute half-life.

A pegylated cyclic peptide that inhibits complement component C3, the central node of all three complement activation pathways (classical, lectin, and alternative). By binding C3 and preventing its cleavage into C3a and C3b, pegcetacoplan blocks both intravascular hemolysis (mediated by membrane attack complex) and extravascular hemolysis (mediated by C3b opsonization and phagocytosis). This dual mechanism addresses the limitation of C5 inhibitors that only prevent intravascular hemolysis.

Peginesatide is a synthetic pegylated peptide-based erythropoiesis-stimulating agent (ESA) consisting of two 21-amino acid chains linked to polyethylene glycol. Unlike recombinant erythropoietin, it contains no erythropoietin sequence homology yet activates the erythropoietin receptor to stimulate red blood cell production. The pegylation confers a prolonged half-life, enabling once-monthly dosing in dialysis-dependent chronic kidney disease.

Eltrombopag is a small-molecule, non-peptide thrombopoietin receptor agonist that binds to the transmembrane domain of the thrombopoietin receptor, distinct from the natural ligand binding site. While not itself a peptide, it mimics thrombopoietin signaling to stimulate megakaryocyte proliferation and platelet production. The oral bioavailability of this synthetic agent addresses limitations of recombinant thrombopoietin peptides, which face immunogenicity challenges.