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Pharmacology · Myeloid colony-stimulating factors

Pegfilgrastim !

Filgrastim joined to polyethylene glycol so it lasts longer: one injection per chemotherapy cycle to prevent febrile neutropenia.

Updated 2026-11-01

The figure shows human G-CSF bound to its receptor; pegfilgrastim is the same protein with a polyethylene glycol chain attached, which is not in the crystal.

Target in 3D: Granulocyte colony-stimulating factor receptor (G-CSFR). PDB structure 2D9Q (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Pegfilgrastim is filgrastim with a polyethylene glycol chain attached. The larger molecule is cleared less by the kidneys and acts for longer, so one injection covers a whole chemotherapy cycle. Its action on the G-CSF receptor is the same as filgrastim.

  1. The drug binds the G-CSF receptor on myeloid progenitors
  2. JAK–STAT signalling drives neutrophil production and maturation
  3. Neutrophils are released sooner from the marrow
  4. Neutropenia is shorter, so fewer infections

Pharmacokinetics

Elimination
Less renal clearance than filgrastim
Half-life
Prolonged, allowing a single dose per chemotherapy cycle

Indications

Adverse effects

Common

  • Bone pain
  • Pain in the limbs
  • Injection-site reactions

Contraindications

  • Serious allergy to pegfilgrastim or filgrastim

Key interactions

Myelosuppressive chemotherapy
Given after the chemotherapy and well before the next cycle, so stimulated cells are not exposed to cytotoxic drugs

What is monitored

  • Complete blood count
  • Bone pain and spleen-related symptoms

Administration and safety

  • Single subcutaneous injection per cycle, typically the day after chemotherapy
  • Not given in the period shortly before the next chemotherapy dose

Nursing care

  • Check the complete blood count as ordered
  • Expect bone pain; report left upper abdominal or shoulder-tip pain at once
  • Teach that infections can still occur: report fever or chills
  • Teach subcutaneous injection and safe disposal if given at home

Pregnancy and breastfeeding

Human data are limited; it is used in pregnancy when the benefit justifies it.

Test yourself

Think of the answer, then tap the question to see it.

What does the polyethylene glycol chain change?

It prolongs action and reduces renal clearance.

How often is it given in chemotherapy?

Once per cycle, after the chemotherapy.

Which receptor does it act on?

The G-CSF receptor, like filgrastim.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Pegfilgrastim Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 45 (McGraw Hill, 2023); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 33 (McGraw Hill, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.