About This Calculator

The SCIG Dose Calculator is a clinical support tool for healthcare professionals to estimate dosing for subcutaneous immunoglobulin (SCIG) therapy. It facilitates dose planning based on patient weight and target dose, assists with converting patients from intravenous immunoglobulin (IVIG), and provides guidance on infusion parameters and ramp-up schedules.

Calculator Outputs Explained

After entering the necessary patient and product data, the calculator provides three main outputs:

• Dosing Recommendation: This section details the core dosing plan, including the total monthly dose in grams (g), the calculated dose per infusion, and the equivalent volume per infusion in milliliters (mL).
• Infusion Plan: Based on the total infusion volume and the maximum volume allowed per injection site, this output calculates the minimum number of sites required and the suggested volume to administer per site. It also provides a range for starting and maximum total infusion rates (mL/hr).
• Ramp-Up Schedule Example: For patients new to SCIG therapy, this section generates a four-week dose titration schedule. It incrementally increases the dose (25%, 50%, 75%, 100%) to help improve tolerability as the patient adjusts to the target maintenance dose.

How to Use the Calculator

1. Enter Patient Data: Input the patient's weight and select the unit (kg or lbs). Choose the appropriate SCIG product from the dropdown list.
2. Define Target Dose: Enter the desired target dose. You can specify this as a weekly dose (mg/kg/wk) or a monthly dose (g/kg/mo) using the toggle buttons. Select the planned dosing frequency (e.g., weekly, biweekly).
3. (Optional) IVIG Conversion: If switching a patient from IVIG, enter their previous IVIG dose in grams, the infusion interval in weeks, and the Dose Adjustment Factor (DAF). The calculator will use this information to determine the equivalent SCIG dose, overriding the target dose entered in step 2.
4. (Optional) Manage Infusion: The tool auto-fills the calculated infusion volume. You can adjust this and the "Max Volume per Site" to see how it affects the required number of infusion sites and suggested administration rates.
5. Calculate: Click the "Calculate" button to generate the dosing, infusion, and ramp-up plans.

Dosing Overview

SCIG therapy is individualized based on clinical response and serum IgG trough levels. The initial dose is often derived from the patient's previous IVIG regimen or based on standard weight-based calculations. The concentration of the SCIG product (e.g., 10%, 16.5%, 20%) directly impacts the volume required for administration; higher concentration products require less volume for an equivalent gram dose. Frequent, smaller infusions (e.g., weekly) often lead to more stable serum IgG levels and may improve tolerability compared to less frequent, larger-volume infusions.

Switching from IVIG to SCIG

When converting a patient from IVIG to SCIG, a Dose Adjustment Factor (DAF) is typically applied to account for the difference in bioavailability. Since SCIG is not fully absorbed into the systemic circulation like IVIG, a higher total dose is needed to achieve a comparable systemic exposure. The DAF commonly ranges from 1.3 to 1.5. This calculator defaults to a DAF of 1.37, but this should be adjusted based on clinical judgment and product-specific recommendations from the prescribing information.

Managing a Missed Dose

If a patient misses a scheduled SCIG dose, it should be administered as soon as they remember. The patient should then resume their regular dosing schedule. If the missed dose is discovered close to the time of the next scheduled dose, the healthcare provider should be consulted. Doubling the dose to make up for a missed one is not recommended. Always refer to the specific product's prescribing information for detailed guidance.

Safety Alerts

Immunoglobulin products, including SCIG, are associated with potential risks. Key safety considerations include:

• Injection Site Reactions: Local reactions such as swelling, redness, itching, and discomfort are common and usually mild to moderate.
• Thrombosis: Arterial and venous thromboembolic events have been reported. Patients with known risk factors should be monitored closely.
• Aseptic Meningitis Syndrome (AMS): AMS can occur, typically within several hours to 2 days following treatment.
• Renal Dysfunction/Failure: Acute renal dysfunction has been reported, particularly with IG products containing sucrose.

This is not a complete list of potential adverse events. Always consult the full prescribing information for the selected product.

Frequently Asked Questions (FAQ)

Why is a Dose Adjustment Factor (DAF) used for IVIG to SCIG conversion?
The DAF compensates for the lower bioavailability of subcutaneously administered immunoglobulin compared to intravenous administration, ensuring the patient achieves a comparable systemic IgG exposure.

How does the calculator determine the number of infusion sites?
It divides the "Total Volume per Infusion" by the "Max Volume per Site" and rounds up to the nearest whole number to ensure the volume at any single site does not exceed the specified maximum.

Can I calculate a dose based on a monthly target (g/kg/mo)?
Yes. In the "Target Dose" field, you can toggle the unit from the default "mg/kg/wk" to "g/kg/mo" to perform calculations based on a monthly dosing target.

What is the purpose of the ramp-up schedule?
The ramp-up, or dose titration, schedule gradually introduces the full SCIG dose over four weeks. This can help improve patient tolerability and minimize local site reactions, especially for patients new to SCIG therapy.

What if my patient’s weight changes significantly?
SCIG dosing is weight-based. If a patient has a significant change in body weight, their dose should be recalculated and adjusted accordingly to maintain therapeutic efficacy.

Does this calculator select the best SCIG product for my patient?
No. The choice of SCIG product depends on clinical factors, patient preference, and formulary access. This tool only calculates the dose for the product you select.

Why are suggested infusion rates provided as a range?
Infusion rates must be individualized. The provided ranges are typical starting points and maximums based on common clinical practice and product labels, but the actual rate should be based on patient tolerance.

Is the calculation for Hyqvia® different from other SCIGs?
Hyqvia is co-administered with recombinant human hyaluronidase, which allows for larger infusion volumes at a single site and less frequent administration (every 3 or 4 weeks). While this calculator computes the gram dose correctly for its 10% concentration, always consult the Hyqvia prescribing information for specific guidance on its unique administration protocol.

References

1. Hizentra® (Immune Globulin Subcutaneous [Human]) 20% Liquid. Full Prescribing Information. CSL Behring. Link to FDA Label
2. Cutaquig® (Immune Globulin Subcutaneous [Human]-hipp) 16.5% Solution. Full Prescribing Information. Octapharma. Link to FDA Label
3. Cuvitru® (Immune Globulin Subcutaneous [Human]) 20% Solution. Full Prescribing Information. Takeda. Link to FDA Label
4. Xembify® (immune globulin subcutaneous, human-klhw) 20% Solution. Full Prescribing Information. Grifols. Link to FDA Label
5. Gammagard Liquid (Immune Globulin Infusion [Human]) 10% Solution. Full Prescribing Information. Takeda. Link to FDA Label (Note: For SC administration details, refer to label sections on SC use).
6. Hyqvia® (Immune Globulin Infusion 10% [Human] with Recombinant Human Hyaluronidase). Full Prescribing Information. Takeda. Link to FDA Label
7. FDA. Drugs@FDA: FDA-Approved Drugs. U.S. Food and Drug Administration. accessdata.fda.gov