C3 glomerulopathy is a rare kidney disease driven by an overactive immune system that gradually damages the kidneys’ ability to filter blood properly, requiring careful management to slow its progression and preserve kidney function for as long as possible.

Understanding Treatment Goals for This Complex Kidney Disease

When someone receives a diagnosis of C3 glomerulopathy, the path ahead focuses on managing a disease that affects how the kidneys work. The main goals of treatment center on slowing down the disease’s progression, reducing the amount of protein being lost in the urine, and protecting whatever kidney function remains. Because this condition tends to worsen gradually over time, early and sustained treatment becomes crucial for maintaining quality of life.^[1]

Treatment strategies depend heavily on how severe the disease is at the time of diagnosis and how each person’s body responds to therapy. For some individuals, the disease may progress slowly with mild symptoms that require only supportive care. For others, more aggressive interventions become necessary to prevent rapid deterioration of kidney function. The approach is always individualized, taking into account the patient’s age, overall health, specific laboratory findings, and whether they have the dense deposit disease (DDD) or C3 glomerulonephritis (C3GN) subtype of the condition.^[3]

Medical societies recognize that C3 glomerulopathy presents unique challenges because it’s so rare—affecting only about 2 to 3 people per million—which makes it difficult to conduct large-scale studies to identify the most effective treatments. Standard approaches borrowed from treating other kidney diseases are commonly used, but researchers continue investigating new therapies specifically designed to target the underlying immune system problems that cause C3 glomerulopathy. Clinical trials play an important role in this evolving landscape, offering patients access to innovative treatments that might not otherwise be available.^[6]

Standard Treatment Approaches

The foundation of standard treatment for C3 glomerulopathy starts with medications that help protect the kidneys from further damage, even though they don’t directly address the underlying immune system problem. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) are commonly prescribed blood pressure medications that do double duty—they lower blood pressure and reduce the amount of protein leaking into the urine. These medications work by relaxing blood vessels and decreasing the pressure inside the kidney’s filtering units, which helps preserve kidney function over time.^[9]

People with C3 glomerulopathy often develop high cholesterol levels as a consequence of their kidney disease. To address this, doctors typically prescribe statins, which are cholesterol-lowering drugs also known as HMG-CoA reductase inhibitors. These medications help reduce cardiovascular risk, which becomes particularly important since kidney disease and heart disease often go hand in hand.^[3]

When the disease is mild—meaning protein levels in the urine are below 1.5 grams per day and kidney function remains relatively normal—this supportive care along with dietary modifications may be sufficient. Patients are typically advised to follow a low-sodium diet (less than 2 grams daily) and sometimes a low-protein diet (around 0.8 grams per kilogram of body weight per day) to reduce the strain on their kidneys.^[12]

Immunosuppressive Medications

For moderate to severe disease—defined as more than 1.5 grams of protein in the urine daily or declining kidney function—doctors often turn to medications that suppress the immune system. The most commonly used combination includes mycophenolate mofetil (MMF) together with corticosteroids (steroids). This combination has shown some promise in clinical practice, with studies suggesting it may help reduce protein loss and slow progression to end-stage kidney disease when used for several years.^[12]

Mycophenolate mofetil works by blocking a specific enzyme needed for certain immune cells to multiply, thereby reducing the immune system’s attack on the kidneys. Corticosteroids like prednisone are powerful anti-inflammatory drugs that broadly suppress immune activity. While this combination can be effective, both medications come with significant side effects. Steroids can cause weight gain, mood changes, increased blood sugar levels, bone thinning, and increased risk of infections. Mycophenolate can cause digestive upset, increased infection risk, and may affect blood cell production.^[9]

Other immunosuppressive medications sometimes used include cyclophosphamide, azathioprine, rituximab, tacrolimus, and sirolimus. These drugs have shown mixed results in different patients, and there’s no one-size-fits-all approach. Each medication carries its own profile of potential side effects, from nausea and hair loss to increased susceptibility to serious infections. Treatment duration varies but typically continues for months to years, depending on how well the disease responds and how well the patient tolerates the medications.^[9]

Plasma-Based Therapies

In certain situations, particularly when someone has a genetic mutation in the complement factor H (CFH) gene, plasma-based treatments may be considered. Plasma replacement therapy involves removing the patient’s blood plasma (the liquid part of blood) and replacing it with donor plasma that contains normal complement proteins. This approach may help control the overactive complement system and slow the progression toward kidney failure in select patients. However, this treatment requires specialized medical facilities and is not suitable for everyone with C3 glomerulopathy.^[3]

Plasmapheresis, another plasma-related treatment, works similarly by filtering the blood to remove harmful antibodies or abnormal proteins that contribute to kidney damage. Results with this approach have been inconsistent, and it’s typically reserved for specific situations where other treatments have failed or when certain autoantibodies are identified in laboratory testing.^[9]

Treatment in Clinical Trials

Because standard immunosuppressive treatments show limited and inconsistent benefits for C3 glomerulopathy, researchers have been investigating therapies that more precisely target the root cause of the disease—the dysregulated complement system. The most extensively studied of these novel treatments is a medication called eculizumab, which represents a new class of drugs called complement inhibitors.^[13]

Complement C5 Inhibition with Eculizumab

Eculizumab is a monoclonal antibody—a laboratory-made protein designed to bind to a specific target in the body. In this case, eculizumab attaches to a complement protein called C5, preventing it from being activated and blocking the formation of the membrane attack complex (MAC). The membrane attack complex is the end product of complement activation that causes direct damage to kidney cells. By stopping this final common pathway, eculizumab aims to halt the ongoing injury to the glomeruli.^[13]

Clinical experience with eculizumab in C3 glomerulopathy has shown mixed results. Some patients, particularly those with a rapidly progressive form of the disease characterized by crescentic glomerulonephritis (severe inflammation with crescent-shaped scars in the kidney tissue), have responded well to treatment. In these cases, kidney function stabilized or even improved, and protein loss in the urine decreased. However, other patients showed little to no benefit, with their disease continuing to progress despite treatment.^[9]

Before starting eculizumab, doctors may measure blood levels of a substance called soluble C5b-9 (also known as sC5b-9). This marker indicates how active the terminal complement pathway is. Studies suggest that patients with elevated soluble C5b-9 levels are more likely to respond positively to eculizumab treatment, though this isn’t a guarantee. The medication is given as an intravenous infusion at regular intervals—initially weekly, then every two weeks for maintenance therapy.^[19]

A significant challenge with eculizumab is that it’s primarily being tested in Phase II and early Phase III studies for C3 glomerulopathy. These phases focus on determining optimal dosing, efficacy compared to standard treatments, and safety profiles in larger patient groups. One retrospective study from Germany examined 11 patients with C3 glomerulopathy treated with eculizumab. Among these patients, five showed stable kidney function during treatment, while six continued to experience decline. The median treatment duration was 10 months, though some patients remained on the medication much longer. This real-world data highlights that while eculizumab can help some patients, it’s not universally effective.^[13]

Other Complement-Targeted Therapies Under Investigation

Given the variable response to C5 inhibition with eculizumab, researchers are exploring other points in the complement cascade where intervention might be more effective for C3 glomerulopathy. Some experimental drugs target the complement system earlier in the activation process, closer to where the initial dysfunction occurs in this disease.^[6]

Several molecules are in various stages of preclinical and early clinical development. These include inhibitors that block complement factor B or factor D, which are essential components of the alternative pathway. By targeting these earlier steps, these investigational drugs aim to prevent the excessive generation of C3 fragments that deposit in the kidneys. Other approaches include engineered versions of naturally occurring complement regulatory proteins, designed to be more stable or more potent than the body’s own regulators.^[6]

Clinical trials investigating these newer agents are primarily in Phase I (focused on safety and initial dosing in small numbers of healthy volunteers or patients) or early Phase II (testing efficacy in larger patient groups with the disease). Because C3 glomerulopathy is so rare, recruiting enough patients for robust clinical trials presents a major challenge. Many trials are conducted at multiple centers internationally, including specialized kidney disease research centers in the United States, Europe, and other regions.^[6]

Patient eligibility for these clinical trials typically requires confirmed diagnosis through kidney biopsy showing the characteristic C3 deposits, evidence of active disease (such as ongoing protein loss in urine), and sometimes specific laboratory findings related to complement testing. Some trials exclude patients who have already progressed to end-stage kidney disease or who have certain genetic mutations, while other studies specifically seek patients with particular genetic profiles to test precision-based approaches.^[11]

FDA-Approved Breakthrough: Iptacopan (Fabhalta)

In a significant development for C3 glomerulopathy treatment, the medication iptacopan, sold under the brand name Fabhalta, recently received FDA approval specifically for adults with this condition. Iptacopan represents a different approach to complement inhibition—it’s a small molecule drug taken by mouth (rather than by infusion) that inhibits complement factor B. By blocking factor B, iptacopan prevents formation of the C3 convertase enzyme complex, which is hyperactive in C3 glomerulopathy. This earlier intervention in the complement cascade may offer advantages over blocking only the terminal pathway. This approval marks the first time any medication has been specifically authorized by regulators for treating C3 glomerulopathy, offering new hope for better disease management and outcomes.^[11]

Most common treatment methods

• Blood pressure medications (ACE inhibitors and ARBs)
  • Prescribed to lower blood pressure and reduce protein loss in urine
  • Help protect kidney function by decreasing pressure in glomeruli
  • Used as first-line therapy for mild disease
  • Typically continued long-term as part of kidney protection strategy
• Cholesterol-lowering medications (Statins)
  • Reduce cardiovascular risk associated with kidney disease
  • Address elevated cholesterol levels that commonly occur with C3G
  • Part of standard supportive care for kidney protection
• Immunosuppressive therapy
  • Mycophenolate mofetil combined with corticosteroids is the most studied combination
  • Reserved for moderate to severe disease with significant protein loss
  • Treatment duration typically spans months to years
  • Other immunosuppressants include cyclophosphamide, azathioprine, rituximab, tacrolimus, and sirolimus
  • Requires careful monitoring for side effects including infection risk
• Complement-targeted therapies
  • Eculizumab blocks complement C5 and prevents membrane attack complex formation
  • Given as intravenous infusion every two weeks after loading doses
  • Most effective in patients with elevated soluble C5b-9 levels or crescentic disease
  • Requires meningococcal vaccination before starting treatment
  • Iptacopan (Fabhalta) is the first FDA-approved oral medication specifically for C3G
  • Works by inhibiting complement factor B earlier in the pathway
• Plasma-based treatments
  • Plasma replacement therapy may benefit patients with CFH gene mutations
  • Plasmapheresis removes harmful antibodies from blood circulation
  • Results have been inconsistent and use is limited to specific situations
  • Requires specialized medical facilities and expertise
• Dietary modifications
  • Low-sodium diet (less than 2 grams daily) reduces kidney strain
  • Low-protein diet (about 0.8 grams per kilogram body weight) may be recommended
  • Helps manage blood pressure and reduce proteinuria
  • Consultation with registered dietitian recommended for meal planning
• Kidney transplantation
  • Option when disease progresses to end-stage kidney disease
  • C3 glomerulopathy recurs in nearly all transplanted kidneys
  • Recurrent disease is major cause of graft failure in 50-90% of cases
  • May require continued complement inhibition after transplant