Pharmacokinetics and administration of colony-stimulating factors

Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) generally are rapidly eliminated from the blood after intermittent intravenous infusion. Subcutaneous administration of these agents results in lower peak concentrations but is associated with prolonged systemic exposure. Elimination of the factors appears to occur by several mechanisms, including white blood cell receptor-mediated endocytosis, metabolism by proteases, and urinary excretion by glomerular filtration with subsequent reabsorption and catabolism. The pattern and route of elimination are affected by type of factor and dosage, degree of glycosylation, renal function, and number of white blood cell receptors for the particular CSF. Granulocyte CSF and GM-CSF are approved for use in patients with nonmyeloid malignancy who are receiving myelosuppressive chemotherapy, and those undergoing high-dose chemotherapy and bone marrow transplantation, respectively. In these indications, treatment generally is initiated no earlier than 24 hours after chemotherapy and continued beyond the expected chemotherapy-associated neutrophil count nadir. Limited information suggests that subcutaneous administration is more effective than intermittent intravenous infusion. The latter may require the addition of albumin to ensure stability. Storage and handling guidelines include preventing exposure to extreme temperatures and avoiding excessive agitation of the solution.