About This Calculator

This Herceptin (trastuzumab) Dosing Calculator is designed to assist healthcare professionals in determining appropriate intravenous (IV) loading and maintenance doses based on patient weight and the selected dosing schedule. It also provides standard administration details for the fixed-dose subcutaneous (SC) formulation.

Outputs Explained

The tool provides the following outputs based on the formulation selected:

• For Intravenous (IV) Formulation:
  • Loading Dose (mg): The initial, higher dose calculated based on body weight (mg/kg).
  • Maintenance Dose (mg): The subsequent, regular dose calculated based on body weight (mg/kg).
  • Vial Suggestion: A calculated combination of 150 mg and 440 mg vials to prepare the required dose with the aim of minimizing waste.
  • Infusion Times: Standard infusion durations for the initial loading dose (90 minutes) and subsequent maintenance doses (30 minutes).
• For Subcutaneous (SC) Formulation:
  • Fixed Dose: Displays the standard 600 mg fixed dose, which is not dependent on patient weight.
  • Administration Details: Notes the standard administration time (2-5 minute injection) and frequency (every 3 weeks).

How to Use the Calculator

1. Select Formulation: Choose between "Intravenous (IV)" or "Subcutaneous (SC)". The available inputs will change accordingly.
2. If IV is selected:
   • Enter the patient's weight into the input field.
   • Select the unit of weight (kg or lbs). The calculator will automatically convert lbs to kg for the calculation.
   • Choose the dosing regimen: "Every 3 Weeks" or "Weekly".
3. If SC is selected: No further inputs are needed. The tool will automatically display the fixed-dose information.
4. Calculate: Click the "Calculate Dose" button to view the results. The output will display the calculated doses and relevant administration information.

Dosing Overview

Intravenous (IV) Administration

IV dosing is weight-based and requires an initial loading dose followed by maintenance doses.

• Every 3 Weeks Schedule:
  • Initial Loading Dose: 8 mg/kg administered over 90 minutes.
  • Maintenance Dose: 6 mg/kg administered over 30 minutes, starting 3 weeks after the loading dose.
• Weekly Schedule:
  • Initial Loading Dose: 4 mg/kg administered over 90 minutes.
  • Maintenance Dose: 2 mg/kg administered over 30 minutes, starting 1 week after the loading dose.

Subcutaneous (SC) Administration

SC administration is a fixed dose, simplifying the process and removing the need for weight-based calculations.

• Fixed Dose: 600 mg administered every 3 weeks, regardless of patient weight.
• No loading dose is required for the subcutaneous formulation.

Switching Between Formulations

Patients may be switched from IV trastuzumab to the SC formulation. The first SC dose of 600 mg should be administered at the next scheduled IV dose. No IV loading dose is needed prior to the switch. When switching from SC to IV, the first IV dose should be administered 3 weeks after the last SC dose. An IV loading dose of 8 mg/kg (for the 3-weekly regimen) or 4 mg/kg (for the weekly regimen) is recommended.

Missed Dose Guidance

Management of a missed dose depends on the duration of the delay:

• If a dose is missed by one week or less: The usual maintenance dose should be given as soon as possible. Do not wait until the next planned cycle.
• If a dose is missed by more than one week: A re-loading dose of IV trastuzumab should be administered as soon as possible (8 mg/kg for q3w, 4 mg/kg for weekly). Subsequent maintenance doses should follow according to the established schedule. For SC, consult the full prescribing information.

Safety Alerts

Cardiotoxicity: Trastuzumab products can result in subclinical and clinical cardiac failure. The incidence and severity were highest in patients receiving trastuzumab with anthracycline-containing chemotherapy regimens. An evaluation of left ventricular ejection fraction (LVEF) is strongly recommended for all patients prior to and during treatment.

Frequently Asked Questions

References

1. Herceptin (trastuzumab) US Prescribing Information. Genentech, Inc. U.S. Food and Drug Administration.
2. Herceptin (trastuzumab) Summary of Product Characteristics (SmPC). European Medicines Agency.
3. Herceptin Official HCP Website. Genentech, Inc.
4. Pivot X, et al. A multicentre, open-label, randomised phase III study to compare the efficacy and safety of subcutaneous versus intravenous trastuzumab in patients with HER2-positive early breast cancer (HannaH study). Lancet Oncol. 2012;13(10):962-970. PubMed.