Gamunex-C is a liquid immune globulin therapy made from donated human plasma. It contains a concentrated solution of IgG antibodies, the same infection-fighting proteins your immune system naturally produces. The product is manufactured by Grifols Therapeutics and is FDA-approved to treat three distinct conditions: primary immunodeficiency (PI), idiopathic thrombocytopenic purpura (ITP), and chronic inflammatory demyelinating polyneuropathy (CIDP).
How Gamunex-C Works
Your blood contains antibodies called immunoglobulins that recognize and neutralize bacteria, viruses, parasites, and toxins. Gamunex-C delivers a broad spectrum of these protective IgG antibodies collected from thousands of plasma donors, giving you access to immune defenses your body may not be producing on its own.
The exact way Gamunex-C works depends on the condition being treated, and the precise mechanisms are not fully understood for any of its three approved uses. In primary immunodeficiency, the infused antibodies essentially replace the ones your body fails to make, reducing how often you get infections. In ITP, where the immune system mistakenly destroys platelets, high doses of immune globulin appear to temporarily block that destructive process and allow platelet counts to recover. In CIDP, a nerve condition, the therapy seems to calm the immune system’s attack on the protective coating around nerves, improving strength and function.
Conditions It Treats
Primary Immunodeficiency
PI refers to a group of inherited conditions in which the body doesn’t produce enough antibodies to fight off infections. People with PI often deal with recurring sinus infections, pneumonia, and other illnesses that healthy immune systems handle easily. Gamunex-C is given every three to four weeks to keep antibody levels high enough to prevent these infections. This is the only condition for which Gamunex-C can be given either intravenously (through a vein) or subcutaneously (under the skin).
Idiopathic Thrombocytopenic Purpura
ITP is an autoimmune condition where the body destroys its own platelets, the blood cells responsible for clotting. This leads to easy bruising, bleeding gums, and tiny red dots on the skin. Gamunex-C is used to rapidly raise platelet counts, typically given over two to five consecutive days depending on the dosing schedule. For ITP, the treatment is only given intravenously, never subcutaneously, because of the risk of bruising and blood pooling at injection sites.
Chronic Inflammatory Demyelinating Polyneuropathy
CIDP is a rare neurological disorder in which the immune system damages the myelin sheath, the insulation around peripheral nerves. This causes progressive weakness, numbness, and tingling in the legs and arms. Gamunex-C treatment for CIDP starts with a loading dose given over two to four days, followed by maintenance infusions every three weeks to prevent symptoms from returning.
How It Is Given
Gamunex-C is a ready-to-use liquid that does not need to be mixed or reconstituted before infusion. It can be administered two ways, depending on the condition.
Intravenous (IV) infusions deliver the medication directly into a vein, typically at an infusion center or hospital. Sessions start at a slow drip and gradually speed up as tolerated. For PI, infusions happen every three to four weeks. For ITP, the treatment is compressed into two to five days. For CIDP, maintenance infusions occur every three weeks after the initial loading period. IV infusions can take several hours depending on the dose and how quickly the rate is increased.
Subcutaneous (SC) infusions are only approved for PI. Instead of a single monthly IV session, the medication is delivered in smaller, more frequent doses, usually weekly, through one or more small needles placed just under the skin of the abdomen, thigh, or upper arm. Adults may use up to eight infusion sites at once, while children use up to six, each spaced at least two inches apart. Many patients learn to do subcutaneous infusions at home, which avoids regular trips to an infusion center. The weekly subcutaneous dose is typically about 37% higher than what the equivalent IV dose would be, because the body absorbs the medication differently through tissue under the skin.
Common Side Effects
Side effects vary depending on the condition being treated and the route of administration. Headache is the most consistently reported reaction across all uses.
For PI patients receiving IV infusions, the most common side effects in clinical trials were cough (31%), runny nose (24%), sore throat (16%), headache (15%), and nausea (12%). These tend to be mild and often improve as the body adjusts to treatment over time.
For PI patients using subcutaneous infusions, reactions at the infusion site are by far the most common issue. In trials, 75% of adults and 100% of children experienced some local reaction, typically redness, swelling, or mild pain where the needle was placed. These reactions usually fade within a day or two and tend to become less noticeable after the first few months of treatment. Fatigue (16%), headache (13%), and upper respiratory infections (13%) were also reported.
ITP patients reported higher rates of headache (52%), which may be related to the larger doses used for this condition. Vomiting (13%), bruising (15%), fever (13%), and nausea (13%) were also common. The headache can sometimes be severe enough to need treatment on its own.
CIDP patients experienced headache (31%), fever (13%), high blood pressure (9%), chills (8%), nausea (6%), and rash (6%) most frequently.
Serious Risks to Know About
While most side effects are manageable, Gamunex-C carries FDA boxed warnings for two serious but rare complications: blood clots and kidney problems.
Blood clots (thrombosis) can occur in arteries or veins after immune globulin infusions, potentially leading to heart attack, stroke, deep vein thrombosis, or pulmonary embolism. Risk is higher in people who are older, have a history of blood vessel disease, use estrogen-based medications, are immobilized for long periods, or have blood that tends to clot easily. Staying well hydrated before and during infusions helps reduce this risk.
Kidney dysfunction, including acute kidney failure, has been reported with IV immune globulin products. People with pre-existing kidney disease, diabetes, or dehydration are at greater risk. The infusion rate also matters: slower infusions are generally gentler on the kidneys.
Allergic reactions, including severe anaphylaxis, are possible. This risk is particularly relevant for people with IgA deficiency, a condition where the body makes little or no IgA (a different type of antibody). If you have IgA deficiency and have developed antibodies against IgA, an immune globulin infusion could trigger a serious allergic reaction.
Because Gamunex-C is made from human plasma, there is a theoretical risk of transmitting infectious agents despite extensive screening and purification of the donor plasma. No cases of viral transmission have been identified with the current manufacturing process, but the risk cannot be completely eliminated.
What the Infusion Experience Is Like
If you’re receiving Gamunex-C intravenously for the first time, expect to spend several hours at an infusion center. The infusion starts slowly so the clinical team can watch for any immediate reactions, then the rate gradually increases if you tolerate it well. Most people sit in a reclining chair and can read, watch something on their phone, or nap during the session. Your first few infusions may take longer than later ones, because the rate is increased more cautiously while your care team learns how you respond.
Subcutaneous infusions at home are shorter and more flexible. After training from a healthcare provider, most people learn the routine within a few sessions. You set up a small pump, insert one or more thin needles into fatty tissue (commonly on the belly or thighs), and let the pump deliver the medication over roughly one to two hours. Weekly subcutaneous infusions tend to keep antibody levels more stable than the peaks and valleys of monthly IV infusions, and some patients find they feel better overall with this approach.
Regardless of the method, treatment with Gamunex-C is ongoing. PI requires lifelong therapy, while ITP and CIDP treatment duration depends on how the condition responds and whether symptoms return when treatment is paused.