PEGFILGRASTIM IS A COVALENT CONJUGATE OF RECOMBINANT METHIONYL HUMAN G-CSF (FILGRASTIM) AND MONOMETHOXYPOLYETHYLENE GLYCOL. BOTH FILGRASTIM AND PEGFILGRASTIM ARE COLONY STIMULATING FACTORS THAT ACT ON HEMATOPOIETIC CELLS BY BINDING TO SPECIFIC CELL SURFACE RECEPTORS, THEREBY STIMULATING PROLIFERATION, DIFFERENTIATION, COMMITMENT, AND END CELL FUNCTIONAL ACTIVATION.1,2 STUDIES ON CELLULAR PROLIFERATION, RECEPTOR BINDING, AND NEUTROPHIL FUNCTION DEMONSTRATE THAT FILGRASTIM AND PEGFILGRASTIM HAVE THE SAME MECHANISM OF ACTION.