Initial Dosing of Trastuzumab for a 77 kg Breast Cancer Patient
For a 77 kg breast cancer patient, the initial loading dose of trastuzumab should be 8 mg/kg IV (616 mg), followed by maintenance doses of 6 mg/kg IV (462 mg) every 3 weeks. 1, 2
Dosing Protocol
Loading Dose
- Initial dose: 8 mg/kg IV (616 mg for a 77 kg patient)
- Administration: As a single intravenous infusion on day 1
Maintenance Dosing
- Subsequent doses: 6 mg/kg IV (462 mg for a 77 kg patient)
- Schedule: Every 3 weeks
- Duration: Typically continued for 1 year in early breast cancer 1
Alternative Dosing Schedule
While the every-3-week schedule is most common and convenient when combined with other chemotherapy agents administered on a 3-weekly basis, an alternative weekly dosing schedule exists:
- Initial dose: 4 mg/kg IV
- Maintenance: 2 mg/kg IV weekly 1
Based on pharmacokinetic analyses, the 3-weekly schedule (8 mg/kg loading, then 6 mg/kg) is considered equivalent to the weekly schedule (4 mg/kg loading, then 2 mg/kg) 1, 3.
Monitoring Requirements
Cardiac monitoring is essential during trastuzumab therapy due to potential cardiotoxicity:
- Baseline cardiac assessment (LVEF measurement)
- Follow-up monitoring at 3,6, and 9 months during treatment 1, 4
- Avoid trastuzumab in patients with low left ventricular ejection fraction (<50-55%) 1
Important Clinical Considerations
- Trastuzumab should not be given concurrently with anthracyclines due to increased risk of cardiotoxicity 1
- It may be administered concurrently with taxanes 1
- The TCH regimen (docetaxel, carboplatin, trastuzumab) is a common non-anthracycline containing regimen that includes trastuzumab 1
- Treatment is typically continued for 1 year in the adjuvant setting 1
Common Side Effects to Monitor
- Infusion-related reactions (fever, chills) - most common during first infusion 2
- Cardiac dysfunction - requires regular monitoring 1, 2
- Fatigue, headache, and rash 2
The 3-weekly dosing schedule offers the advantage of convenience for patients while maintaining equivalent efficacy to weekly dosing, and has been well-established in clinical practice for HER2-positive breast cancer treatment.