Final answer:
Filgrastim primarily increases white blood cell production by stimulating the differentiation of myeloblasts into granular leukocytes such as neutrophils, which helps combat neutropenia in patients with conditions like multiple myeloma, especially those receiving chemotherapy.
Step-by-step explanation:
The primary action of filgrastim is to increase white blood cell production. Filgrastim is a type of colony-stimulating factor (CSF), specifically a granulocyte CSF, which stimulates the differentiation of myeloblasts into granular leukocytes such as neutrophils. It is a glycoprotein that acts as an autocrine or paracrine factor, enhancing the proliferation and differentiation of white blood cells to combat neutropenia, a condition characterized by low levels of neutrophils. In the context of multiple myeloma and other cancers, filgrastim is administered to patients undergoing chemotherapy to help revive their WBC counts, thereby improving their immune system's ability to fight infections.