Ziltivekimab sharply lowered inflammation, yet cardiovascular events held steady
Neutralizing interleukin-6 with ziltivekimab produced a marked biologic effect in patients with established atherosclerotic cardiovascular disease and chronic kidney disease, but the clinical payoff never materialized. In a large multinational randomized trial, the drug drove down free interleukin-6 and high-sensitivity C-reactive protein at 24 months, yet the rate of major adverse cardiovascular events was essentially identical to placebo over a median 33 months of follow-up.
The result is difficult to ignore because the trial enrolled a population where inflammatory risk should have been especially relevant. Patients had established atherosclerotic cardiovascular disease, chronic kidney disease, and evidence of cardiovascular inflammation defined by high-sensitivity CRP of at least 2 mg per liter. That combination creates a biologic setting in which interleukin-6 signaling seems plausible as a treatment target: chronic inflammation promotes endothelial dysfunction, plaque instability, and thrombotic activation, while kidney disease amplifies inflammatory burden and cardiovascular risk.
A large, high-risk cohort with persistent inflammatory activity
The study included 6376 patients in the full analysis population, with 3184 assigned to ziltivekimab and 3192 to placebo. The mean age was 69.4 years, and 27.5% of participants were women. Those baseline features matter clinically because this was not a low-risk prevention cohort. These were older patients with established vascular disease and renal impairment, the kind of population in which residual inflammatory risk can remain high even when conventional risk factors are treated aggressively.
Participants received subcutaneous ziltivekimab, 15 mg once monthly, or placebo in a double-blind, randomized, placebo-controlled design. The primary efficacy end point was a 3-point major adverse cardiovascular event composite of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke. That endpoint is familiar to cardiology because it captures the outcomes most closely tied to plaque rupture and arterial thrombosis, and it is the correct test for any anti-inflammatory strategy claiming vascular benefit.
The biomarker data showed that the drug was not pharmacologically inert. At 24 months, the between-group difference in the median percent change favored ziltivekimab by 76 percentage points for free interleukin-6 and by 64 percentage points for high-sensitivity CRP. Those shifts confirm that IL-6 blockade reached its target and materially altered the inflammatory milieu. In mechanistic terms, this is the sort of biomarker suppression one would expect if the pathway were central to the downstream cardiovascular phenotype.
It was not enough.
No reduction in major adverse cardiovascular events
During follow-up, a primary end-point event occurred in 561 patients, or 17.6%, in the ziltivekimab group and in 565 patients, or 17.7%, in the placebo group. The hazard ratio was 0.99, with a 95% confidence interval from 0.88 to 1.11, and the P value was 0.84. Those figures leave little room for a hidden cardiovascular benefit in the studied population. Event curves did not separate in a clinically meaningful way, despite the clear biologic suppression of inflammatory markers.
For clinicians, the disconnect is more instructive than a simple negative result. It suggests that lowering circulating interleukin-6 and CRP in this setting does not automatically translate into fewer myocardial infarctions, strokes, or cardiovascular deaths. One possible explanation is that inflammation may be a marker of advanced vascular disease rather than the dominant driver of events in this subgroup. Another is that the pathway may need to be blocked earlier, more intensely, or in a different phenotype of atherosclerosis to affect hard outcomes. The trial does not answer those questions, but it does constrain the optimism that biomarker improvement alone should guide treatment adoption.
Safety was broadly similar, with more serious infections in the active arm
Serious adverse events occurred in 54.6% of patients receiving ziltivekimab and 54.8% of those receiving placebo, so overall serious toxicity was broadly comparable. Serious infections were reported in 20.4% and 17.9%, respectively. Even without a large overall safety imbalance, that infection signal matters in a population already burdened by chronic kidney disease and vascular comorbidity, where immune modulation can carry clinical costs that are not trivial.
The safety profile fits the broader immunology of IL-6 blockade. Interleukin-6 is a key mediator of acute phase responses, host defense signaling, and inflammatory amplification. Suppressing it can lower CRP and other biomarkers, but the same mechanism can weaken protective immune responses and may increase susceptibility to infection. In a population with chronic illness and older age, even a modest increase in serious infections can influence the risk-benefit calculation, especially when the cardiovascular endpoint remains unchanged.
The study’s main message is straightforward: a strong anti-inflammatory signal did not produce a cardiovascular outcome signal. That should prompt caution whenever biomarker suppression is treated as proof of clinical efficacy. In atherosclerosis, the biology is real, but it is not always sufficient to move the events that matter most at the bedside.
What the ZEUS trial means for anti-inflammatory cardiovascular therapy
The trial’s implications reach beyond ziltivekimab itself. Cardiovascular medicine has already seen that some anti-inflammatory strategies can reduce ischemic events, while others fail despite convincing changes in inflammatory markers. This study adds another example of pathway specificity: not every inflammatory target maps onto the same clinical outcome, and not every biomarker response predicts vascular protection.
For patients with concomitant atherosclerotic cardiovascular disease and chronic kidney disease, the result is particularly important because this is a group with few easy therapeutic options for residual risk. The negative outcome does not erase the biologic plausibility of IL-6 inhibition, but it does weaken the case for routine use of ziltivekimab as a cardiovascular risk-reduction strategy in this population. The practical consequence is that treatment decisions should remain anchored to proven therapies for secondary prevention rather than to inflammatory biomarker improvement alone.
The trial was funded by Novo Nordisk and carried the ZEUS ClinicalTrials.gov identifier NCT05021835. Its design and scale make the findings hard to dismiss, and its biomarker effect makes the neutral cardiovascular result even more consequential. Future work will have to determine whether another IL-6–directed strategy, another dose, or another patient subset can do what this one could not: turn inflammation suppression into fewer deaths, infarctions, or strokes.