About This Content

This information provides a clinical overview of the principles used in the Hizentra Dose Calculator. It is intended to supplement the tool by explaining its calculations, parameters, and the underlying dosing guidelines from the Prescribing Information for Primary Immunodeficiency (PI) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) indications.

Calculator Outputs Explained

Upon entering the required patient data, the calculator generates a comprehensive dosing regimen that includes:

• Hizentra Dose: The final calculated dose for the selected frequency, shown in both grams (g) and total volume (mL).
• Recommended Vial Combination: A practical supply estimate suggesting the number and size of vials (5, 10, 20, or 50 mL) to achieve the target volume with minimal waste. The total volume is always rounded up to the nearest 5 mL increment.
• Infusion Site Planning: The recommended number of simultaneous infusion sites, calculated to ensure no single site receives more than the maximum recommended volume of 25 mL.
• Volume Per Site: The average volume to be administered at each injection site for the planned infusion.

How to Use the Calculator

Follow these steps to determine the appropriate Hizentra dose and administration plan:

1. Enter Patient Weight: Input the patient’s weight and select the unit (kg or lbs). The tool will convert lbs to kg automatically.
2. Select Indication: Choose either Primary Immunodeficiency (PI) or CIDP.
3. Specify PI Patient Status: If PI is selected, indicate if the patient is switching from intravenous immune globulin (IVIG) or is treatment-naïve / switching from another subcutaneous immune globulin (SCIG).
4. Choose Dosing Frequency (PI): For PI patients, select the desired administration schedule (weekly or bi-weekly). CIDP is calculated as a weekly dose.
5. Enter Prior/Target Dose: For IVIG switches, provide the previous total IVIG dose in grams and the dosing interval. For naïve patients, enter the target weekly SCIG dose in mg/kg.

Dosing Overview

The calculator’s logic is based on the approved dosing guidelines in the Hizentra Prescribing Information.

• For Primary Immunodeficiency (PI):
  • Naïve or Switching from SCIG: Dosing is based on a target weekly dose, typically between 100-200 mg/kg, as determined by the healthcare provider.
  • Switching from IVIG: The previous IVIG dose is converted to an equivalent subcutaneous dose using a dose adjustment factor of 1.37. This adjusted monthly dose is then divided to determine the weekly or bi-weekly Hizentra dosing schedule.
• For Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): The recommended maintenance dose is 0.2 g/kg of body weight administered weekly. The PI notes this may be increased to 0.4 g/kg weekly based on clinical response.

Switching from IVIG to Hizentra

When switching a patient from IVIG to Hizentra for a PI indication, a dose adjustment is necessary to account for differences in bioavailability. The calculator automates this by multiplying the equivalent monthly IVIG dose by a factor of 1.37 to establish the new total monthly subcutaneous dose. This new total is then divided by 4 for a weekly schedule or by 2 for a bi-weekly schedule to determine the dose for each infusion.

Managing a Missed Dose

Guidance on managing a missed dose is not provided by this calculator. Healthcare professionals should consult the full official Prescribing Information for detailed instructions, as the appropriate action depends on the length of the delay and the patient’s specific clinical context. Do not double the next dose without consulting the PI.

Safety Alerts and Clinical Notes

This tool is a clinical aid and not a substitute for professional medical judgment. Always refer to the most current, full Prescribing Information for complete safety details, warnings, and contraindications. Key considerations reflected in the tool include:

• A dose ramp-up may be necessary for PI patients, especially those who are naïve to SCIG therapy.
• The maximum recommended volume per infusion site is 25 mL.
• The maximum recommended infusion rate per site is 25 mL/hour as tolerated.

Frequently Asked Questions (FAQ)

Why is the Hizentra dose higher when switching from IVIG?
The dose is adjusted by a factor of 1.37 to compensate for the lower systemic bioavailability of subcutaneous administration compared to intravenous administration, ensuring a comparable therapeutic effect.

How does the calculator determine the number of infusion sites?
It divides the total calculated dose volume (in mL) by the maximum recommended volume per site (25 mL) and rounds up to the nearest whole number to ensure no site is overloaded.

What vial sizes does the calculator use for its supply estimate?
The tool optimizes the combination using commercially available Hizentra vial sizes: 5 mL, 10 mL, 20 mL, and 50 mL.

Does the calculator schedule the initial dose ramp-up for PI patients?
No, the calculator determines the steady-state maintenance dose. The initial dose ramp-up protocol should be implemented according to the Prescribing Information and clinical judgment.

Can I use this tool for a patient with a CIDP diagnosis requiring a bi-weekly schedule?
The tool calculates the CIDP dose based on the approved weekly schedule (0.2 g/kg). Any alternative schedule would be considered off-label and should be based on clinical discretion and the full Prescribing Information.

How is a bi-weekly dose calculated for PI?
The tool first calculates the equivalent weekly dose based on the patient’s status (IVIG switch or naïve) and then doubles that amount to determine the bi-weekly dose.

Why is the “Total Volume from Vials” sometimes higher than the calculated dose volume?
To ensure the full dose can be administered, the tool recommends a vial combination that meets or exceeds the target volume, rounding up to the nearest 5 mL increment. This may result in a small amount of overage.

What conversion factor is used for weight from pounds to kilograms?
The calculator uses the standard conversion factor of 1 lb = 0.453592 kg (or 1 kg ≈ 2.20462 lbs).

References

1. Hizentra (Immune Globulin Subcutaneous [Human]) 20% Liquid – Full Prescribing Information. U.S. Food and Drug Administration. Revised: August 2023.
2. Hizentra for Healthcare Professionals – Dosing and Administration. CSL Behring.
3. Drugs@FDA Database: Hizentra. U.S. Food and Drug Administration.
4. Shapiro R. Subcutaneous immunoglobulin therapy: a new option for patients with primary immunodeficiency diseases. Biologics. 2010;4:101-111. Published 2010 Jun 1.