pegfilgrastim
Meaning of pegfilgrastim: A single injection after chemotherapy that pushes the marrow to make infection-fighting white cells, replacing a run of daily shots.
Definition of pegfilgrastim
Pegfilgrastim is a laboratory-made version of granulocyte colony-stimulating factor, the natural signal that tells bone marrow to produce neutrophils. Attaching a polyethylene glycol chain to the protein slows its removal from the blood, so one injection lasts through the period of risk. It is given after chemotherapy to shorten the stretch when the white cell count is dangerously low.
Why is it needed after chemotherapy?
Chemotherapy targets rapidly dividing cells, and the bone marrow is full of them. Neutrophil production falls for roughly a week to ten days after a cycle, and neutrophils are the white cells that deal with bacterial infection first. When their number drops far enough, an infection can become severe with very few outward signs, since much of what is recognized as infection is the immune response itself. A fever during that window is treated as an emergency for this reason.
How does the pegylated form differ from the original?
| Filgrastim | Pegfilgrastim | |
|---|---|---|
| Structure | The protein alone | Protein with a glycol chain attached |
| Clearance | Filtered by the kidney | Too large to filter, removed by neutrophils |
| Dosing | Repeated daily injections | One injection per cycle |
The clearance route makes the timing self-adjusting. Neutrophils themselves take up and destroy the drug, so while counts are low the drug persists, and as counts recover it is cleared faster.
What does it actually do in the marrow?
It binds receptors on immature cells committed to becoming a neutrophil, telling them to divide, mature faster and leave the marrow sooner. Mature neutrophils also work somewhat more actively. It does not raise other blood cell lines, so it does not help anemia or a low platelet count. The natural signal it copies is granulocyte colony-stimulating factor, produced by cells lining the vessels and by immune cells during infection. Bone pain, felt in the pelvis, spine and long bones as the marrow becomes crowded, is the most familiar side effect.
Also known as
Used in a sentence
Pegfilgrastim was given after each cycle to reduce the risk of febrile neutropenia.
Good to know
Pegfilgrastim raises neutrophils only and has no effect on red cells or platelets, so anemia and low platelet counts after chemotherapy are unchanged by it.