About This Tool

This brand-agnostic SCIG Dose Calculator is a clinical support resource designed for healthcare professionals to estimate subcutaneous immunoglobulin (SCIG) dosing for patients with immune deficiencies. It provides calculations for two common scenarios: initiating therapy in a new patient and converting a patient from intravenous immunoglobulin (IVIG) to SCIG.

Understanding the Outputs

After entering the required parameters, the calculator provides a comprehensive dosing summary:

• Total Dose per Infusion: The total amount of immunoglobulin in grams (g) for a single administration session based on the selected frequency.
• Total Volume per Infusion: The total liquid volume in milliliters (mL) required for the infusion, determined by the dose and product concentration.
• Minimum Number of Sites: The calculated number of injection sites needed, based on the total volume and the maximum volume allowed per site.
• Volume per Site: The approximate volume (mL) to be administered at each injection site.
• Estimated Minimum Infusion Time: A time estimate in minutes, calculated from the total volume, number of sites, and maximum rate per site. Actual time may vary based on patient tolerance.

How to Use the Calculator

Select the appropriate tab based on your patient’s clinical situation.

For New Patient Dosing: This module is for patients starting SCIG therapy without a prior history of IVIG. You will need to input the patient’s weight, the desired weekly dose (e.g., 100-200 mg/kg/week), the SCIG product concentration, and the desired dosing frequency (e.g., weekly, bi-weekly).

For IVIG to SCIG Conversion: This module is for patients switching from a stable IVIG regimen. Enter the patient’s weight, their previous total IVIG dose in grams, the IVIG infusion interval, a dose adjustment factor (typically 130-152%), the target SCIG frequency, and the SCIG product concentration.

Dosing Overview

SCIG dosing is individualized based on the patient’s clinical response, serum IgG trough levels, and tolerability. For primary immunodeficiency diseases (PIDD), a common starting dose is 100-200 mg/kg per week. Doses are often initiated with a ramp-up or titration schedule over several weeks to ensure patient comfort and tolerance to the infusion volume. Regular monitoring of serum IgG levels is recommended, with dose adjustments made to maintain levels within the therapeutic range and prevent infections.

Switching from IVIG

When converting a patient from IVIG to SCIG, a dose adjustment is necessary to account for the difference in bioavailability. SCIG has lower systemic bioavailability compared to IVIG. Therefore, the total monthly SCIG dose needs to be higher than the previous IVIG dose to achieve comparable serum IgG levels. A dose adjustment factor, often around 137% but ranging from 130% to 152% depending on the specific product and clinical guidelines, is applied to the previous equivalent weekly IVIG dose to determine the target weekly SCIG dose.

Missed Dose Guidance

If a patient misses a dose, it should be administered as soon as possible. The subsequent dosing schedule should then be adjusted to maintain the correct interval. For example, if a patient on a weekly schedule misses a dose by three days, they should take the dose immediately and resume their regular weekly schedule from that new day. Consult product-specific prescribing information for detailed guidance.

Safety Alerts

This information is not a substitute for clinical judgment or official prescribing information.

• Local Site Reactions: Redness, swelling, itching, and discomfort at the infusion site are common and usually mild to moderate and transient.
• Systemic Reactions: Headache, fatigue, and fever can occur but are less common than with IVIG.
• Thrombosis: Immune globulin products have been associated with a risk of thrombotic events. Ensure patients are not volume-depleted before administration.
• Aseptic Meningitis Syndrome (AMS): AMS can occur with IG therapy, typically within hours to 2 days of treatment. It is more common with IVIG but has been reported with SCIG.

Frequently Asked Questions (FAQ)

1. Why is a dose adjustment factor needed for IVIG to SCIG conversion?
The adjustment factor (e.g., 137%) compensates for the lower bioavailability of subcutaneously administered IgG compared to intravenously administered IgG, ensuring comparable systemic exposure and efficacy.

2. What should I do if my product’s concentration isn’t listed?
Select the “Other” option from the “SCIG Product Concentration” dropdown menu. A new field will appear where you can manually enter the correct concentration percentage.

3. Can I use this calculator for a specific brand of SCIG?
Yes, this calculator is brand-agnostic. You can use it for any SCIG product by inputting the correct concentration (10%, 16.5%, 20%, or a custom value). However, always cross-reference the results with the product’s official prescribing information.

4. How is the minimum number of infusion sites determined?
The calculator divides the total infusion volume by the “Max Volume per Infusion Site” you define in the parameters. It then rounds up to the nearest whole number to ensure no site receives more than the specified maximum volume.

5. Is the “Estimated Minimum Infusion Time” the actual time it will take?
It is an estimate based on the maximum infusion rate per site. The actual time may be longer, especially during the initial ramp-up phase or if a lower rate is used for patient tolerance.

6. What is a typical ramp-up schedule?
A new patient often starts at 25% of the target volume for the first week, increasing to 50%, 75%, and finally 100% over the subsequent weeks. The calculator includes a button to generate a sample 4-week ramp-up schedule after the initial calculation.

7. Why can the SCIG dosing frequency be more flexible than IVIG?
Subcutaneous administration leads to more stable serum IgG levels, which allows for a variety of dosing schedules, from daily to bi-weekly, depending on patient preference and the total volume required.

8. What is a typical maximum volume and rate per infusion site?
This varies by product and patient tolerance. Common initial values are 20-25 mL/site at a rate of 15-20 mL/hr/site. As tolerated, these can be increased, with some products allowing for higher volumes and rates. Always consult the product monograph.

References

• 1. Gernez, Y., & Jolles, S. (2017). Practical guidance for the use of subcutaneous immunoglobulin in patients with primary immunodeficiencies. Clinical & Experimental Immunology, 188(3), 329–342. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5422830/
• 2. Shapiro, R. S. (2010). A practical guide to the use of subcutaneous immunoglobulin in patients with primary immune deficiency. Current allergy and asthma reports, 10(1), 13–18. https://pubmed.ncbi.nlm.nih.gov/20425482/
• 3. U.S. Food and Drug Administration. (2023). Immune Globulins. https://www.fda.gov/vaccines-blood-biologics/approved-blood-products/immune-globulins
• 4. Provan, D., Chapel, H., & Sewell, W. A. C. (2019). Clinical guidelines for immunoglobulin use, 3rd edition. UK Department of Health.