IVIG Dose Calculator

What is IVIG?

Intravenous immunoglobulin (IVIG) is a blood product prepared from the pooled plasma of thousands of healthy donors. It contains primarily immunoglobulin G (IgG) antibodies and is used to treat a wide range of immunological, neurological, and hematological conditions. IVIG works through multiple mechanisms including modulation of the immune system, blocking Fc receptors, providing passive immunity, and suppressing inflammatory pathways.

IVIG has been available since the 1980s and is one of the most commonly used blood-derived therapies worldwide. It is manufactured through a complex fractionation process that involves cold ethanol precipitation, chromatography, and viral inactivation steps to ensure safety and purity. Major commercial brands include Gamunex-C, Privigen, Octagam, Gammagard, and Panzyga, among others.

The demand for IVIG has grown substantially over the past decades as new indications have been identified. Because it is derived from human plasma, IVIG is an expensive therapy (often costing thousands of dollars per infusion) and can be subject to supply shortages. This has led to the development of subcutaneous immunoglobulin (SCIG) as an alternative route of administration for some indications, particularly primary immunodeficiency.

Indications and Dosing

IVIG is approved or commonly used for numerous conditions. The dose varies significantly depending on the indication, and correct dosing is critical for both efficacy and safety:

Indication	Dose	Regimen
Immune Thrombocytopenia (ITP)	1 g/kg	1-2 days
Kawasaki Disease	2 g/kg	Single infusion
Guillain-Barré Syndrome (GBS)	0.4 g/kg/day	5 consecutive days (total 2 g/kg)
Primary Immunodeficiency (PID)	0.4-0.6 g/kg	Every 3-4 weeks
CIDP	1 g/kg	Loading; then 0.4-1 g/kg every 3-4 weeks
Multifocal Motor Neuropathy	1-2 g/kg	Every 2-4 weeks
Myasthenia Gravis (exacerbation)	1-2 g/kg	Over 2-5 days

Dosing by Condition

Immune Thrombocytopenia (ITP): ITP is an autoimmune condition causing low platelet counts and increased bleeding risk. IVIG at 1 g/kg is given as a single dose or over two days, typically when rapid platelet count elevation is needed (e.g., before surgery or with active bleeding). The response is usually rapid but temporary, with platelet counts rising within 24-48 hours and the effect lasting 2-4 weeks.

Kawasaki Disease: Kawasaki disease is a childhood vasculitis that can cause coronary artery aneurysms. IVIG at 2 g/kg as a single infusion, given with aspirin, is the standard treatment. This is the highest single-dose indication for IVIG and should be administered within the first 10 days of illness for maximum benefit in preventing coronary complications.

Guillain-Barré Syndrome (GBS): GBS is an acute inflammatory demyelinating polyneuropathy. The standard IVIG regimen is 0.4 g/kg/day for 5 consecutive days (total dose of 2 g/kg). This regimen is as effective as plasma exchange and is often preferred due to its ease of administration. Treatment should be initiated within 2 weeks of symptom onset for best results.

Primary Immunodeficiency (PID): Patients with primary antibody deficiencies require lifelong immunoglobulin replacement therapy. The typical dose is 0.4-0.6 g/kg every 3-4 weeks, with the goal of maintaining trough IgG levels above 500-800 mg/dL (or higher, depending on clinical response and individual patient needs).

Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): CIDP is a chronic autoimmune neuropathy. The loading dose is typically 1-2 g/kg over 2-4 days, followed by maintenance doses of 0.4-1 g/kg every 3-4 weeks. IVIG is a first-line treatment for CIDP and has been shown to improve both disability and quality of life.

Obesity Adjustment

Dosing IVIG in obese patients (BMI ≥ 30 kg/m²) presents a unique challenge. Using actual body weight in obese patients can lead to excessive dosing, increasing the risk of adverse effects (particularly thromboembolic events, renal impairment, and volume overload) and increasing costs. Most guidelines recommend using an adjusted body weight for obese patients.

The adjusted body weight formula uses the ideal body weight (IBW) as a baseline and adds 40% of the excess weight above IBW. This approach accounts for the fact that while adipose tissue does have some blood supply and extracellular fluid, it does not distribute IgG to the same extent as lean tissue. The 0.4 correction factor is widely used in clinical practice for IVIG dosing, though some institutions may use slightly different factors.

This calculator automatically detects obesity (BMI ≥ 30) and switches to adjusted body weight. For non-obese patients, actual body weight is used for dosing. Always consult with a pharmacist or prescribing physician for final dose verification, particularly in complex patients.

Infusion Procedure

IVIG administration requires careful preparation and monitoring throughout the infusion. The procedure typically follows these steps:

1. Pre-medication: Many protocols include pre-medication with acetaminophen, diphenhydramine, and sometimes corticosteroids (e.g., methylprednisolone) to reduce the risk of infusion reactions. Adequate hydration before and during the infusion is also recommended.
2. Initial rate: Infusions typically begin at a slow rate (0.5-1 mL/kg/hr) for the first 30 minutes. If tolerated, the rate is gradually increased.
3. Rate escalation: The infusion rate is typically doubled every 15-30 minutes if no adverse reactions occur, up to a maximum rate that varies by product (typically 4-8 mL/kg/hr).
4. Monitoring: Vital signs (blood pressure, heart rate, temperature, respiratory rate) are monitored at baseline, with each rate change, and at regular intervals throughout the infusion.
5. Duration: A typical IVIG infusion takes 4-6 hours, though this varies based on the dose, product concentration, and individual patient tolerance.

For patients receiving IVIG for the first time, extra caution is warranted as the risk of adverse reactions is highest with initial infusions. Subsequent infusions may be administered at faster rates if previous infusions were well-tolerated.

Side Effects and Precautions

IVIG is generally well-tolerated but can cause a range of adverse effects. Most are mild and infusion-related, but serious complications can occur:

• Common (10-20%): Headache, fever, chills, fatigue, nausea, myalgia, back pain. These often resolve with slowing the infusion rate or pre-medication.
• Moderate: Migraine, aseptic meningitis (severe headache with neck stiffness, usually within 48 hours), transient hypertension, flushing, urticaria.
• Serious (rare): Thromboembolic events (DVT, pulmonary embolism, stroke, MI), acute renal failure (particularly with sucrose-containing products), hemolytic anemia (due to anti-A/anti-B antibodies in the product), transfusion-related acute lung injury (TRALI), anaphylaxis (especially in IgA-deficient patients with anti-IgA antibodies).

Risk factors for thromboembolic events include advanced age, immobility, cardiovascular risk factors, hypercoagulable states, and high-dose IVIG regimens. Adequate hydration and slower infusion rates can help mitigate this risk. Renal function should be monitored, especially in patients with pre-existing renal impairment, diabetes, or those receiving nephrotoxic medications concurrently.

Worked Example

A 45-year-old male patient weighing 110 kg and 175 cm tall is diagnosed with Guillain-Barré Syndrome. Calculate the IVIG dose.

First, calculate BMI: BMI = 110 / (1.75)² = 110 / 3.0625 = 35.9 kg/m² (obese)

Since BMI ≥ 30, use adjusted body weight:

GBS dose: 0.4 g/kg/day for 5 days. Daily dose = 0.4 × 86.3 = 34.5 g/day. Total course = 34.5 × 5 = 172.5 g.

Number of 5g vials per day = 34.5 / 5 = 6.9, round up to 7 vials/day (35 vials total for the course).

Frequently Asked Questions

Why is IVIG so expensive?

IVIG is derived from human plasma collected from thousands of donors, requiring extensive screening, fractionation, purification, and viral inactivation processes. The manufacturing process is time-consuming and complex, and the raw material (human plasma) is inherently limited. A single treatment course can cost $5,000-$30,000 or more depending on the dose and indication.

Can IVIG be given subcutaneously?

Yes, subcutaneous immunoglobulin (SCIG) is an alternative for certain indications, primarily primary immunodeficiency. SCIG allows patients to self-administer at home, which improves convenience and quality of life. However, SCIG is not appropriate for all indications and requires more frequent administration (usually weekly) with smaller volumes per site.

Why is obesity adjustment needed?

IgG distributes primarily in lean tissue and plasma. Using actual body weight in obese patients would result in higher doses than necessary, increasing the risk of adverse effects (especially thromboembolic events and renal complications) and cost without proportional clinical benefit. Adjusted body weight accounts for the reduced distribution of IgG in adipose tissue.

How many vials should I order?

IVIG is typically available in 5g, 10g, 20g, and sometimes 25g vials. The calculator shows the number based on 5g vials. In practice, round up to the nearest available vial size. Some institutions allow partial vial use if the product will be used promptly, while others require using whole vials to minimize waste and contamination risk.

Are there any contraindications to IVIG?

The primary absolute contraindication is a history of anaphylaxis to immunoglobulin products. Patients with selective IgA deficiency who have anti-IgA antibodies are at risk for anaphylaxis and should receive IgA-depleted products if IVIG is required. Relative contraindications include renal insufficiency, hypercoagulable states, and congestive heart failure (due to volume load).

How long does the effect of IVIG last?

The duration of IVIG effect varies by indication. For ITP, the platelet response typically lasts 2-4 weeks. For immunodeficiency, trough levels guide dosing frequency (usually every 3-4 weeks). For neurological conditions like GBS, IVIG is given as a single course, while CIDP often requires ongoing maintenance therapy. The half-life of infused IgG is approximately 21-28 days.