Pegcetacoplan vs Ravulizumab for PNH Treatment

Pegcetacoplan and ravulizumab both treat paroxysmal nocturnal hemoglobinuria (PNH) by blocking the complement system, but they do so at fundamentally different points in the cascade, and that distinction drives most of the clinically meaningful differences between them. Pegcetacoplan targets C3, a protein near the top of the complement pathway, while ravulizumab targets C5, a protein further downstream. That gap in where each drug intervenes shapes how well each one controls the two types of red blood cell destruction that make PNH so debilitating, and it also affects infection risk, dosing logistics, and cost.

Why the Point of Intervention Matters

PNH destroys red blood cells because a genetic mutation leaves them unprotected against complement, a branch of the immune system that normally tags and destroys invaders. The complement cascade works like a chain reaction: early proteins activate middle ones, which activate late ones, which ultimately punch holes in cell membranes. Ravulizumab blocks C5, one of the last steps in that chain. Pegcetacoplan blocks C3, which sits at the convergence point where all three activation routes of complement funnel together before cascading downstream.¹

Blocking at C5 stops the final membrane-attack complex from forming, which prevents the explosive destruction of red blood cells inside blood vessels (intravascular hemolysis). But C5 inhibition leaves the earlier complement fragments, particularly C3b, free to coat red blood cells. Those tagged cells get gobbled up by the spleen and liver, a process called extravascular hemolysis. Patients on C5 inhibitors can therefore still be anemic and tired even though their most dramatic lab markers improve. Pegcetacoplan, by blocking at C3, intercepts both the downstream membrane attack and the upstream tagging that leads to extravascular destruction.²

What the Trial Evidence Actually Shows

There is no randomized head-to-head trial directly comparing pegcetacoplan with ravulizumab. That gap is one of the most frustrating things about the PNH treatment landscape, and it forces clinicians to piece together indirect comparisons. What does exist is a direct trial against eculizumab, the older C5 inhibitor that ravulizumab was engineered to replace.

In the PEGASUS trial, patients who had a suboptimal response to eculizumab were randomized to switch to pegcetacoplan or continue eculizumab. By week 16, the pegcetacoplan group saw hemoglobin levels rise by roughly 4 g/dL more than the eculizumab group, and 85% of pegcetacoplan patients no longer needed transfusions, compared with 15% on eculizumab.³ Those gains held through the 48-week extension.⁴

Ravulizumab’s own pivotal trials compared it to eculizumab and showed non-inferiority across all efficacy and safety endpoints, both in patients who had never been on a C5 inhibitor and in those switching from eculizumab.⁵ Ravulizumab was designed to have a longer half-life than eculizumab, delivering the same C5 blockade with less frequent dosing.⁶ So ravulizumab is essentially a more convenient version of eculizumab, while pegcetacoplan showed superiority over eculizumab in hemoglobin gains and transfusion freedom.

Because no head-to-head trial exists between pegcetacoplan and ravulizumab, researchers have used matching-adjusted indirect comparisons, a statistical technique that tries to balance patient characteristics across separate trials. One such analysis in eculizumab-experienced patients found similar effects on LDH normalization (a marker of intravascular hemolysis), but pegcetacoplan showed better control of both intravascular and extravascular hemolysis.⁷ Indirect comparisons carry inherent uncertainty, though, and the field is well aware that they are no substitute for a proper randomized trial.

Breakthrough Hemolysis

One area where ravulizumab appears to have an edge is breakthrough hemolysis, episodes where complement activity temporarily overwhelms the drug and red blood cell destruction flares. A review of breakthrough events across phase 3 trials found that ravulizumab had a frequency of less than 5% over six months, while pegcetacoplan, eculizumab, and crovalimab each showed rates in the range of 10% to 15%. When the follow-up period extended to a year, the frequency with pegcetacoplan climbed to around 24%, higher than with C5 inhibitors or the newer alternative-pathway inhibitors.⁸

The reasons for this difference are not entirely settled, but the pharmacology offers some clues. Ravulizumab provides very consistent C5 blockade between doses because of its engineered long half-life, leaving fewer windows for complement to sneak through. Pegcetacoplan requires more frequent self-injections, and if a dose is delayed or absorption varies, there is more opportunity for complement to reactivate. Breakthrough events on pegcetacoplan do not necessarily mean the patient is worse off overall, since hemoglobin levels between episodes can remain higher than on C5 therapy, but they can be alarming and occasionally require transfusions.

Quality of Life and Fatigue

How patients feel day to day is arguably more important than any lab value. In a matching-adjusted indirect comparison of eculizumab-experienced patients, those on pegcetacoplan reported larger improvements in fatigue, physical functioning, and overall health status than those on ravulizumab at 26 weeks. The fatigue improvement on pegcetacoplan was clinically meaningful (well above the threshold considered noticeable), while the ravulizumab group’s improvement did not cross that threshold.⁹ That makes intuitive sense: if pegcetacoplan is driving hemoglobin higher by addressing both types of hemolysis, people feel less exhausted.

However, a separate matching-adjusted indirect comparison in treatment-naïve patients found no statistically significant difference between pegcetacoplan and ravulizumab on fatigue, physical functioning, or fatigue-symptom scores.¹⁰ The discrepancy probably reflects the patient populations: people already on eculizumab who still have residual anemia (often driven by extravascular hemolysis) stand to gain more from C3 inhibition than patients starting treatment fresh, since the unmet need is different.

Within the PEGASUS trial itself, about 72% of pegcetacoplan-treated patients reached a clinically meaningful improvement in fatigue scores, compared with about 23% on eculizumab.¹¹ Since ravulizumab performs roughly on par with eculizumab for quality-of-life measures, this hints at the scale of pegcetacoplan’s advantage in the suboptimal-responder population, though again, the comparison is indirect.

Infection Risk and Vaccination

Any drug that disables part of the complement system raises concerns about infections with encapsulated bacteria, especially meningococcal disease. The complement pathway’s membrane-attack complex is one of the body’s key defenses against these organisms. Patients on either drug must be vaccinated against meningococcus, and many carry prophylactic antibiotics.

A pooled safety analysis of over 1,700 patients with systemic pegcetacoplan exposure, spanning clinical trials and post-marketing data, found a meningococcal sepsis rate of 0.04 per 100 patient-years, with no cases of encapsulated meningitis. By comparison, registry data from patients on eculizumab or ravulizumab reported meningococcal infection rates of 0.12 per 100 patient-years in Japan and 0.35 per 100 patient-years in the United Kingdom.¹²

These numbers are drawn from different data collection systems (clinical trial databases versus national registries), so they are not perfectly comparable. Still, the finding aligns with what the mechanism would predict. C5 blockade eliminates the membrane-attack complex entirely while leaving C3-mediated opsonization intact, so bacteria that rely on being cleared through C3-tagged pathways might survive if those routes are also impaired. Pegcetacoplan blocks C3, which would seem more dangerous for infection, yet the early data suggest the opposite. One explanation is that systemically delivered pegcetacoplan may not fully suppress complement in all tissue compartments, leaving some residual bacterial clearance capability that is lost when C5 is completely blocked. Regardless of mechanism, vaccination and antibiotic prophylaxis remain non-negotiable for both drugs.

Dosing and Administration

How a drug is given matters enormously for people with a lifelong disease. Ravulizumab is administered by intravenous infusion every eight weeks after an initial loading dose. Each infusion takes roughly an hour or two at an infusion center. Pegcetacoplan is given by subcutaneous injection, typically every three days for the standard dose of 1,080 mg, though a pump or syringe allows self-administration at home. Some patients move to a weekly schedule at a higher dose.

For some people, the every-eight-week infusion visit is manageable and even reassuring, since a healthcare provider monitors each session. For others, especially those who live far from an infusion center or whose schedules make regular visits difficult, self-injection at home offers more flexibility. The trade-off is that pegcetacoplan’s more frequent dosing demands discipline: missing or delaying injections increases the risk of breakthrough hemolysis.

Switching from a C5 inhibitor like ravulizumab to pegcetacoplan requires a bridging period. For the first four weeks, pegcetacoplan is given twice weekly alongside the ongoing C5 inhibitor to prevent a surge in hemolysis from abrupt complement reactivation. After four weeks, the C5 inhibitor is discontinued and pegcetacoplan continues as monotherapy.¹³ This overlap is critical because stopping C5 inhibition suddenly leaves patients with no complement blockade until pegcetacoplan reaches therapeutic levels, a window that could trigger severe hemolysis.

Cost and Health-Economic Modeling

Both drugs are extraordinarily expensive, as are all complement inhibitors for PNH. But economic modeling consistently favors pegcetacoplan over ravulizumab. A UK-based cost-effectiveness analysis of eculizumab-experienced patients found that pegcetacoplan produced both lower lifetime costs and greater quality-adjusted life years than ravulizumab.¹⁴ A US-based analysis in treatment-naïve patients estimated lifetime savings of roughly $213,000 with pegcetacoplan compared with ravulizumab, with a small gain in quality-adjusted life years as well.¹⁵

A European analysis put the five-year per-patient cost at roughly €1.48 million for pegcetacoplan versus €1.57 million for ravulizumab, with pegcetacoplan also delivering more quality-adjusted life years and lower transfusion-related expenses.¹⁶ Much of the cost savings comes from reduced transfusion needs rather than a lower list price for the drug itself. These are model-based analyses, and their conclusions depend on assumptions about long-term hemoglobin stability, breakthrough event rates, and drug pricing, all of which can shift. But the direction of the finding has been consistent across settings.

Beyond PNH

Both molecules are being studied or used outside PNH, and their paths diverge sharply because of where each blocks complement. Ravulizumab has expanded into other complement-driven disorders where C5 blockade is effective: it is approved for atypical hemolytic uremic syndrome and generalized myasthenia gravis, and long-term data from a trial in aquaporin-4-antibody-positive neuromyelitis optica spectrum disorder showed a safety profile consistent with its other indications.¹⁷

Pegcetacoplan, meanwhile, has found an entirely separate niche through a different delivery route. As an intravitreal injection directly into the eye, it became the first FDA-approved treatment for geographic atrophy secondary to age-related macular degeneration in February 2023.¹⁸ In that condition, complement overactivation in the retina drives progressive vision loss, and C3 sits at the convergence point of the pathways involved.¹⁹ The ophthalmic form is delivered locally in tiny volumes and has nothing to do with systemic complement suppression, but it underscores how the C3 target opens up therapeutic territory that a C5 inhibitor cannot reach.

There is also growing interest in C3-level inhibition for kidney diseases like C3 glomerulopathy and IgA nephropathy, where overactive alternative-pathway complement deposits C3 fragments in the kidney. Blocking at C3 is expected to yield greater control over this pathologic deposition than C5-targeted therapy, because the problem originates upstream of C5.²⁰ Ravulizumab has not been pursued in these particular renal conditions, which illustrates how the two drugs’ mechanisms naturally channel them toward different disease landscapes.

Who Gets Which Drug

In practice, the choice between pegcetacoplan and ravulizumab often comes down to whether a patient still has significant residual anemia on a C5 inhibitor. A person who started on ravulizumab (or eculizumab) and whose hemoglobin remains stubbornly low, who still needs transfusions, or who battles persistent fatigue despite good LDH control is the textbook candidate for switching to pegcetacoplan. The residual anemia in this setting is usually driven by extravascular hemolysis, which only C3 inhibition addresses.

Conversely, a patient who is well controlled on ravulizumab, with stable hemoglobin and minimal symptoms, has less reason to switch, especially considering the bridging period required and the higher rate of breakthrough events reported with pegcetacoplan. Some patients also prefer the every-eight-week infusion schedule over frequent self-injections, a preference that is entirely valid and can affect adherence.

For treatment-naïve patients, the choice is less clear-cut. The indirect evidence suggests pegcetacoplan may offer somewhat better hemoglobin outcomes, but the quality-of-life differences in this population appear smaller. Access, insurance coverage, and patient preference for infusion versus self-injection often tip the scale. The complement-inhibitor landscape is also expanding rapidly, with newer oral and subcutaneous options targeting factor B and factor D entering the picture, which may reshape these decisions in the next few years.

Pegcetacoplan’s Ophthalmic Life

It is worth pausing on how unusual it is for a single molecule to have two entirely distinct clinical identities. In hematology, pegcetacoplan is a systemic subcutaneous drug given every few days for a blood disorder. In ophthalmology, it is an intravitreal injection given monthly or every other month for a retinal disease. The underlying mechanism is the same: suppress C3 to tamp down complement-mediated damage. But the formulations, dosing, safety concerns, and patient populations have almost nothing in common. Ophthalmologists evaluating pegcetacoplan for geographic atrophy are thinking about endophthalmitis risk and retinal detachment, not meningococcal prophylaxis. Hematologists prescribing it for PNH have never seen a case of geographic atrophy. The drug lives a double life, and its two user communities rarely overlap.