Human immunoglobulin-G

• Replacement therapy (Primary and secondary antibody deficiency)
• Replacement of IgG to prevent infections in primary immunodeficiency diseases (PIDs) such as common variable immunodeficiency, X-linked agammaglobulinemia, and other disorders with impaired antibody production.
• Replacement in secondary immunodeficiencies associated with e.g., hematological malignancy, post-stem cell transplant, or other causes when hypogammaglobulinemia with recurrent infections is documented.
• Immunomodulatory / therapeutic uses (high-dose IVIG)
• Autoimmune and inflammatory disorders where pooled IgG exerts immunomodulatory effects, e.g.: idiopathic thrombocytopenic purpura (ITP), Guillain–Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), Kawasaki disease, certain dermatomyositis and selected neurologic or hematologic conditions. Evidence and licensure vary by indication and product.
• Post-exposure prophylaxis (select agents)
• Specific preparations or pathogen-specific immune globulins are used for post-exposure prophylaxis (e.g., hepatitis A, measles in selected persons) per public-health guidance; dosing and product choice depend on indication.

Dosing varies markedly by indication (replacement vs immunomodulation), patient weight, clinical response and product—doses below are general, clinically used regimens; individual product labels and institutional protocols must be followed.

• Replacement therapy (primary immunodeficiency) — IVIG
• Typical maintenance: 300–600 mg/kg (0.3–0.6 g/kg) administered every 3–4 weeks for most patients; many centers target trough IgG levels tailored to infection control (common starting guidance: 400–600 mg/kg every 3–4 weeks). Dose and interval are adjusted to clinical response and trough IgG.
• Replacement therapy — SCIG
• Typical total monthly dose: similar cumulative monthly dose to IVIG, often delivered as weekly or twice-weekly SC infusions; initial SC dose may be calculated as ~1.37 × equivalent IV monthly dose when switching from IV to SC to maintain steady troughs. Dosing frequency and site volumes depend on product concentration (e.g., 10%, 20% formulations) and device (pump vs push).
• Immunomodulatory (high-dose) IVIG
• Common regimens: 0.4 g/kg/day for 5 days (total ~2 g/kg) or 1 g/kg/day for 2 days (total ~2 g/kg) are frequently used in immune-modulation (e.g., GBS, ITP acute regimens); dosing and infusion rates depend on indication and product.
• Pediatric dosing
• Replacement pediatric doses are similar on a mg/kg basis to adults; Kawasaki disease uses age-specific high-dose IVIG regimens (e.g., 2 g/kg as single infusion) per pediatric cardiology/infectious-disease protocols.
• Elderly / renal or hepatic impairment
• No routine dose reduction solely for age, hepatic or renal disease is universally recommended; caution in severe renal impairment—choose products with lower sucrose or stabilizer load and monitor renal function. Individualize dosing and infusion rate.
• Administration route & technique
• IVIG: intravenous infusion with gradual escalation of infusion rate if tolerated; premedication (antipyretic, antihistamine, corticosteroid) may be used for patients with prior infusion reactions. Observe during and after infusion.
• SCIG: subcutaneous infusion by pump or manual push; rotate infusion sites, maintain aseptic technique.
• Missed doses / switching
• For replacement, resume therapy as soon as possible; do not double doses. When switching IV⇄SC, adjust dose per conversion factors and monitor trough IgG and clinical response.

Human immunoglobulin preparations are pooled polyclonal IgG derived from healthy donor plasma. For replacement therapy, they provide passive humoral immunity by supplying a broad repertoire of antibodies that neutralize pathogens, opsonize bacteria for phagocytosis, and restore deficient serum IgG levels to prevent infections. For immunomodulatory effects at high doses, IgG exerts multiple mechanisms including Fc receptor blockade, modulation of complement activation, neutralization of autoantibodies, inhibition of pathogenic cytokines, modulation of B- and T-cell function, and interference with idiotype–anti-idiotype networks—collectively reducing pathogenic immune activity in autoimmune disorders.

• Absorption & distribution: IVIG is delivered directly into the bloodstream; SCIG is absorbed slowly from subcutaneous tissue into systemic circulation producing more stable serum IgG levels. IgG distributes in the intravascular and extravascular compartments.
• Half-life: The typical IgG half-life after infusion is approximately 21–28 days (range ~18–32 days), though individual variability exists.
• Metabolism & elimination: IgG is catabolized by proteolytic pathways (FcRn receptor-mediated salvage influences IgG half-life) rather than hepatic CYP metabolism; catabolic fragments are cleared via normal protein degradation pathways. Renal excretion of intact IgG is minimal under normal renal function.
• Onset & duration of effect: Replacement raises serum IgG and provides immediate passive protection; trough levels decline over weeks and determine infusion intervals. Immunomodulatory effects may occur during and shortly after high-dose administration.

• Pregnancy: IVIG is not absolutely contraindicated in pregnancy; it has been used for specific indications in pregnancy (e.g., certain obstetric immunologic conditions, some cases of immune thrombocytopenia, or primary immunodeficiency) when benefit outweighs risk. Decision should be individualized; pregnancy testing is not universally required before replacement dosing but is often used when high-dose immunomodulatory IVIG would be considered.
• Lactation: IgG is a normal component of human milk; IVIG given to a lactating mother is not contraindicated and no specific infant adverse effects have been consistently identified—routine breastfeeding may continue. Monitoring is prudent if high-dose regimens are used but overall data support safety in breastfeeding.

• Primary therapeutic class: Immunoglobulin replacement / immunomodulatory biologic therapy.
• Subclass: Pooled human normal immunoglobulin (IgG); administered intravenously (IVIG) or subcutaneously (SCIG); some products are liquid formulations (5% or 10%) or lyophilized; some are virus-inactivated and/or specially purified to reduce adverse events.

• Known anaphylactic reaction to human immunoglobulin preparations or to any component of a specific product (e.g., trace IgA content may provoke reactions in patients with anti-IgA antibodies).
• Selective IgA deficiency with anti-IgA antibodies and a history of severe reactions to IgA-containing products—use cautiously and consider IgA-depleted products or alternative strategies.
• Hypersensitivity to specific excipients (check product label).

• Severe infusion reactions / anaphylaxis: Immediate allergic reactions can occur; staff and equipment for emergency management must be available. Observe during infusion, especially first doses.
• Thromboembolic events: IVIG has been associated with arterial and venous thrombosis; assess and mitigate risk (hydration, slower infusion rate, consider thrombosis risk factors).
• Renal dysfunction / acute renal failure: Rare but serious renal adverse events reported—use caution in patients with preexisting renal disease, diabetes, volume depletion, or when using products containing certain stabilizers (e.g., sucrose); monitor renal function and consider selecting non-sucrose formulations.
• Transfusion-related acute lung injury (TRALI) and pulmonary complications: Monitor respiratory status.
• Aseptic meningitis: Rarely reported—new severe headache, neck stiffness, or photophobia warrant evaluation.
• Infectious agent transmission risk: Plasma-derived products are processed to reduce risk, but theoretical residual risk exists; use licensed products and follow blood-product safety guidance.

• Common / mild
• Infusion-related: headache, flushing, chills, fever, malaise, myalgia, low back pain, nausea. Local injection-site reactions with SCIG (erythema, swelling, itching).
• Less common / serious
• Severe allergic reaction/anaphylaxis, aseptic meningitis, acute renal failure, hemolytic anemia (rare; can occur due to passive anti-A/B antibodies), thromboembolic events, TRALI.
• Timing & dose-dependence
• Mild infusion reactions typically occur during or within 24–48 hours of infusion and often improve with slower infusion rates or premedication. Serious events can be immediate or delayed—monitor for new symptoms post-infusion.

• Vaccine interactions: IVIG can interfere with the immune response to live viral vaccines (e.g., measles, varicella, rubella); administration of live vaccines may be deferred for several months after high-dose IVIG (check vaccine and product guidance).
• Laboratory assay interference: Passive antibodies may transiently interfere with serologic testing (e.g., hepatitis B surface antibody, certain viral serologies, and antibody titers).
• Pharmacologic interactions: No CYP-mediated metabolic drug interactions are expected. Monitor for interaction with concomitant therapies that affect thrombosis risk or renal function.

• Regulatory guidance and clinical practice emphasize individualized dosing based on clinical outcomes and trough IgG monitoring rather than fixed mg/kg alone; many centers aim to titrate dose to achieve minimal infection frequency and acceptable trough IgG.
• SCIG has become an increasingly used option for many PID patients for home administration to improve quality of life and provide steady IgG levels; conversion factors from IVIG to SCIG dosing are widely adopted in practice.
• Product-specific guidance continues to evolve regarding infusion rates, renal safety, and selection of stabilizers—clinicians should follow the latest product and institutional protocols.

• General storage: Follow each product’s label—many liquid IVIG products are stored refrigerated at 2°C to 8°C; do not freeze. Lyophilized products require reconstitution per instructions and have defined in-use stability after reconstitution.
• Light & humidity: Keep in original carton to protect from light.
• Handling precautions: Inspect vial for particulate matter or discoloration; do not use compromised product. Use aseptic technique; discard any unused reconstituted solution per product instructions. Maintain cold chain for storage and transport.