Management of Anastrozole-Induced Neutropenia
For patients experiencing neutropenia due to anastrozole therapy, discontinue the medication and initiate granulocyte colony-stimulating factor (G-CSF) therapy until neutrophil recovery, then consider alternative hormonal therapy options. 1
Assessment of Neutropenia Severity
- Neutropenia is defined as an absolute neutrophil count (ANC) < 1,500/mcL 2
- Severity classification:
- Mild: ANC 1,000-1,500/mcL
- Moderate: ANC 500-1,000/mcL
- Severe: ANC < 500/mcL 3
- Monitor complete blood counts with differential to track neutrophil levels and recovery 1
- Assess for signs of infection, particularly fever, which requires immediate intervention 1
Immediate Management
For Non-Febrile Neutropenia:
- Discontinue anastrozole immediately 1
- Consider G-CSF (filgrastim) at 5 μg/kg/day subcutaneously until neutrophil recovery (ANC > 1,000/mcL) 1
- Monitor blood counts frequently (initially weekly) until recovery 1
- Provide patient education about infection precautions 1
For Febrile Neutropenia (Temperature ≥38.0°C):
- Hospitalize for immediate intervention 1
- Obtain blood cultures and other relevant cultures before starting antibiotics 1
- Initiate empiric broad-spectrum antibiotics within 2 hours of presentation 1
- Consider an antipseudomonal beta-lactam (piperacillin-tazobactam, cefepime, or carbapenem) as monotherapy 1
- Add G-CSF (filgrastim) 5 μg/kg/day until neutrophil recovery 1
- Continue antibiotics until neutropenia resolves and patient is afebrile for at least 48 hours 1
Prophylaxis During Neutropenia
- Antibacterial prophylaxis: Consider fluoroquinolone (levofloxacin or ciprofloxacin 500 mg daily) if ANC < 500/mcL 1
- Antifungal prophylaxis: Fluconazole 400 mg daily if neutropenia is expected to be prolonged 1
- Antiviral prophylaxis: Acyclovir 400 mg or valacyclovir 500 mg twice daily 1
- Continue prophylaxis until ANC recovers to > 500/mcL 1
Long-term Management
- After neutrophil recovery, consider alternative hormonal therapy options for breast cancer treatment 1
- Options include:
- Different aromatase inhibitor (exemestane or letrozole)
- Selective estrogen receptor modulators (tamoxifen)
- Fulvestrant (estrogen receptor antagonist) 1
- Monitor blood counts more frequently when initiating alternative therapy 1
- If neutropenia recurs with alternative aromatase inhibitors, switch to a different class of hormonal therapy 1
Special Considerations
- Neutropenia is not commonly reported with anastrozole but can occur as an idiosyncratic reaction 4
- Evaluate for other potential causes of neutropenia (infections, other medications, bone marrow disorders) 3, 5
- Consider bone marrow examination if neutropenia is severe or prolonged despite drug discontinuation 5
- Assess for other potential complications of anastrozole therapy, including renal dysfunction 4
Follow-up Recommendations
- Weekly blood counts until ANC normalizes 1
- After recovery and initiation of alternative therapy, monitor blood counts every 2 weeks for the first month, then monthly for 3 months 1
- Long-term monitoring every 3 months for the first year after the neutropenic episode 1
- Educate patient about reporting fever or signs of infection promptly 1