What medications are contraindicated with filgrastim (Granulocyte-Colony Stimulating Factor, G-CSF) injection?

Filgrastim Contraindications and Critical Drug Interactions

Filgrastim is absolutely contraindicated during concurrent chest/thoracic radiotherapy due to significantly increased complications and mortality risk. 1, 2

Absolute Contraindication

Concurrent Chest Radiotherapy

• Do not administer filgrastim during any radiotherapy to the chest - this is the only true absolute contraindication consistently emphasized across all major guidelines 1, 2
• This contraindication is based on documented increased rates of complications and death in patients receiving concurrent chest radiation 1
• The European Society for Medical Oncology (ESMO) gives this the highest level of evidence (Level I, Grade A) 1

Critical Timing Restrictions (Not Absolute Contraindications, But High-Risk)

Chemotherapy Administration Timing

• Never administer filgrastim on the same day as chemotherapy - this creates severe risk of thrombocytopenia and increased febrile neutropenia 2, 3, 4
• Do not give filgrastim within 24 hours before chemotherapy - immediate pre-chemotherapy administration significantly increases risk of severe thrombocytopenia 1, 2, 3
• Wait 24-72 hours after completing chemotherapy before initiating filgrastim to avoid these complications 2, 3, 4

The rationale here is that stimulating rapidly dividing neutrophil precursors during active chemotherapy exposure makes them more vulnerable to cytotoxic damage, paradoxically worsening outcomes 1.

Clinical Situations Where Filgrastim Should NOT Be Used

Non-Neutropenic Patients

• Do not use filgrastim in patients without documented neutropenia, especially those with community-acquired or hospital-acquired pneumonia 1, 3
• This is emphasized by both ESMO and the American College of Physicians with Level I, Grade A evidence 1
• Using G-CSF in non-neutropenic patients with pneumonia provides no benefit and may cause harm 1

Pediatric Acute Leukemias

• Avoid routine use in pediatric AML/ALL due to theoretical concerns about stimulating leukemic blast cell growth 2, 3
• The American Society of Clinical Oncology specifically recommends against routine filgrastim use in these populations 2, 3

Important Drug-Related Precautions (Not True Contraindications)

Pegfilgrastim-Specific Restrictions

• Do not use pegfilgrastim for therapeutic treatment of established febrile neutropenia - only filgrastim or sargramostim are appropriate in this acute setting 4
• Do not use the 6 mg pegfilgrastim formulation in patients weighing <45 kg due to excessive dosing risk 2

Common Pitfalls to Avoid

• Do not target ANC >10,000/mm³ - recovery to 2,000-3,000/mm³ is sufficient, and excessive stimulation should be avoided 2, 3, 4
• Monitor for severe thrombocytopenia when timing is suboptimal, even if not given simultaneously with chemotherapy 1, 3
• Monitor CBC twice weekly during filgrastim administration to detect complications early 4

Summary of True Contraindications

Based on the highest quality guideline evidence, there is essentially one absolute medication/treatment contraindication: concurrent chest radiotherapy 1, 2. The other restrictions are critical timing issues and inappropriate clinical scenarios rather than traditional drug-drug contraindications. No specific medications are listed as absolute contraindications to filgrastim use in the available evidence.