Pegfilgrastim

Pegfilgrastim is filgrastim bound to polyethylene glycol, giving a long-acting granulocyte colony-stimulating factor that is given once for each chemotherapy cycle to reduce febrile neutropenia.

Classification. Haematopoietic growth factor; long-acting granulocyte colony-stimulating factor.

Mechanism. Like filgrastim, it stimulates neutrophil proliferation, differentiation and release. Clearance depends on neutrophil receptors, so it is self-regulating.

Pharmacokinetics. Half-life is 15 to 80 hours, and falls as the neutrophil count recovers. Large size delays renal clearance.

Prevention of febrile neutropenia after chemotherapy (adults).

• Dose: 6 mg subcutaneously once each cycle, at least 24 hours after chemotherapy.
• Do not give in the 14 days before the next chemotherapy. Not suitable for cycles shorter than 14 days.
• Maximum: one dose each cycle. Loading dose and titration: not applicable.

Children. Under 45 kg: 100 µg/kg once each cycle. At 45 kg or more: 6 mg. Some labels set weight bands; confirm locally.

Adjustments. Kidney and liver: no adjustment. Older adults: no adjustment.

Contraindications. Hypersensitivity. Not used for stem cell mobilisation.

Warnings. Splenic rupture, acute respiratory distress syndrome, capillary leak, glomerulonephritis, sickle cell crisis, leukocytosis, aortitis. Myelodysplasia or leukaemia risk in some cancer settings.

Adverse effects. Bone pain (very common), headache, nausea, injection-site reaction, raised alkaline phosphatase.

Interactions. Not given within 14 days before or 24 hours after cytotoxic chemotherapy. Lithium enhances neutrophil release.

Pregnancy and breastfeeding. Limited data; use only if essential.

Regional points. Cost and cold chain limit supply; filgrastim may be the only option.

Common errors. Giving too close to the next cycle; repeating in the same cycle; treating weekly regimens.

Administration. Subcutaneous injection into abdomen, upper arm or thigh. Store at 2 to 8°C. Prefilled syringe and on-body injector forms exist.

Baseline. Full blood count with differential, spleen examination.

Monitoring. Full blood count before each cycle; neutrophil nadir count. Review spleen and chest symptoms.

Referral and escalation. Left upper quadrant or shoulder pain: urgent imaging. Breathing difficulty with infiltrates: stop and assess for capillary leak or respiratory distress syndrome.