Subcutaneous Immunoglobulin (SCIg)
Weekly home injections that eliminate infusion center visits and the wearing-off effect
Route
Subcutaneous injection
Frequency
Once weekly (typical)
Setting
Home self-administration
FDA Status
FDA-approved for CIDP maintenance
Educational use only. This page explains how SCIg works based on clinical guidelines and trial data. It cannot replace your neurologist. All treatment decisions must be made with your medical team.
How SCIg Works
Subcutaneous immunoglobulin (SCIg) delivers the same pooled human immunoglobulin as intravenous IVIG, but through small needles placed under the skin rather than into a vein. The immunological mechanism is identical to IVIG — the key difference is pharmacokinetics: SCIg's slower, continuous absorption produces much more stable blood IgG levels.
- •Same immunological mechanisms as IVIG: Fc receptor blockade, complement inhibition, anti-idiotypic antibodies, regulatory T-cell modulation
- •Absorbed slowly through the subcutaneous lymphatic system rather than directly into the bloodstream
- •Weekly smaller doses (vs. monthly large IVIG doses) result in steady-state IgG trough levels — the "peaks and troughs" of IVIG are eliminated
- •Steady levels mean IgG never falls below the therapeutic threshold — eliminating the wearing-off effect
- •Self-administered at home using a small pump, fine needles (4–8mm), and 1–6 injection sites simultaneously
- •Hizentra and Cuvitru are 20% concentration formulations, allowing smaller injection volumes
Clinical Evidence
SCIg is non-inferior (clinically equivalent) to IVIG for CIDP maintenance therapy, established by the Phase 3 PATH study (NEJM 2017/2018). The PATH study is the largest CIDP trial to directly compare both routes of immunoglobulin delivery.
| Metric | Value | Source |
|---|---|---|
| Equivalence to IV IVIG | Non-inferior | PATH Study, NEJM 2017/2018 |
| Relapse risk reduction vs. placebo | Significant (both IVIG and SCIg arms) | PATH Study |
| Wearing-off episodes vs. IVIG | Significantly reduced | Patient-reported outcomes, PATH |
| FDA approval (Hizentra) | 2018 for CIDP | FDA |
| FDA approval (Cuvitru) | 2018 for CIDP | FDA |
| Typical weekly dose | ~0.2–0.4 g/kg/week | Standard conversion from IVIG |
SCIg dose is typically calculated by dividing the patient's monthly IVIG dose by 4 (or the biweekly dose by 2) to approximate equivalent weekly dosing. Individual titration is common based on IgG trough levels and clinical response.
Patients who switch from IVIG to SCIg specifically to address wearing-off almost universally report improvement in end-of-cycle symptoms. The steady IgG level means symptom stability throughout the week rather than peaking and declining.
Side Effects
Common
- •Local injection site reactions: temporary lumps (pseudocysts), redness, itching, or mild swelling — resolve within hours
- •Mild headache (less common than with IVIG due to slower absorption)
- •Local bruising at injection sites
- •Transient soreness during and after injections
Serious (less common)
- •Systemic reactions (rare with SCIg vs. IVIG): fever, chills, nausea — occur if infusion rate is too fast
- •Anaphylaxis: very rare; same IgA deficiency warning applies as with IVIG
- •Infection at injection site (uncommon with proper technique)
Systemic side effects (headache, fever, fatigue) that are common with IVIG are significantly less frequent with SCIg because the slow subcutaneous absorption prevents the blood level spikes that trigger these reactions. Local site reactions are the primary trade-off — they're almost universal in the first weeks but typically diminish as the skin adapts to regular injections.
Pros & Cons
Advantages
- ✓Home self-administration — no infusion center visits
- ✓Eliminates wearing-off effect (steady weekly IgG levels)
- ✓Fewer systemic side effects than IVIG (no headache/fever spikes)
- ✓More flexible scheduling (split across multiple days if preferred)
- ✓Same clinical efficacy as IVIG (Level A evidence, PATH study)
- ✓Both Hizentra and Cuvitru have robust patient support programs
Drawbacks
- –Requires weekly self-injections and training
- –Pump, supplies, and needles add equipment burden
- –Local site reactions in early weeks
- –Not suitable for patients with poor subcutaneous tissue (very thin or scarred)
- –Insurers may require documented IVIG use first before approving home SCIg
- –Weekly discipline required — missing doses affects blood levels
Insurance & Access
- →Typically covered similarly to IVIG — Medicare Part B and most commercial insurers; prior authorization required
- →Many insurers require documentation of prior IV IVIG use, though this is not a clinical requirement (it is a coverage requirement)
- →Home health nurse training visit at initiation is usually covered and necessary for insurance approval
- →Hizentra: CSL Behring offers the "HIZENTRA CARES" program with copay assistance and nursing support
- →Cuvitru: Takeda offers the "IMMUNOGLOBULIN THERAPY" support program
- →If your IVIG prior authorization is approved, ask your neurologist's office to simultaneously submit for SCIg — many patients prefer to switch once they learn about home administration
Have a question about SCIg?
Ask the AI assistant for more detail — dosing questions, wearing-off, insurance appeals, how SCIg compares to other options, and more.
Ask the AI →Other CIDP Treatments
IVIG
The most widely used first-line treatment for CIDP, with Level A evidence
Vyvgart Hytrulo
First FDA-approved FcRn inhibitor for CIDP — a 30-second weekly injection at home
Plasma Exchange
A fast-acting procedure that physically removes harmful antibodies from the blood
Corticosteroids
Oral or IV steroids that broadly suppress immune activity — effective but with long-term trade-offs
Sources
- van Schaik IN, et al. Subcutaneous immunoglobulin for maintenance treatment in CIDP (PATH Study). N Engl J Med. 2018;378(9):802–812.
- FDA. Approval of Hizentra for CIDP. 2018.
- FDA. Approval of Cuvitru for CIDP. 2018.