ODYSSEY OUTCOMES Trial: A Plain-English Overview of What It Established

At a glance

Detail	Value
Full title	Alirocumab and Cardiovascular Outcomes after Acute Coronary Syndrome
Registry	NCT01663402
N	18,924
Population	Adults 1 to 12 months post-ACS, LDL ≥70 mg/dL on maximally tolerated statin
Intervention	Alirocumab 75 mg or 150 mg SC every 2 weeks
Comparator	Matching placebo injections every 2 weeks
Duration	Median follow-up 2.8 years
Primary endpoint	Composite MACE: coronary heart disease death, nonfatal MI, ischemic stroke, or unstable angina requiring hospitalization
Key result	HR 0.85 (95% CI 0.78, 0.93; P <0.001), a 15% relative risk reduction
Sponsor	Sanofi / Regeneron
Published	2018, New England Journal of Medicine (PubMed)

The Question Behind the Trial

By the mid-2010s, statins had a long track record of lowering LDL cholesterol and reducing heart attacks and strokes, but a sizable group of patients still had events despite taking the strongest tolerated statin dose. PCSK9 inhibitors, a newer class of injectable drugs, could lower LDL by an additional 50 to 60% on top of a statin. The open question was whether that extra LDL lowering would translate into fewer heart attacks, strokes, and deaths, or whether it would only move a lab number.

The FOURIER trial, published in 2017, had already shown that evolocumab, a different PCSK9 inhibitor, reduced cardiovascular events in a broad population with established atherosclerotic disease. ODYSSEY OUTCOMES asked the same question for alirocumab, in a higher-risk group: patients who had recently had an acute coronary syndrome (ACS), meaning a heart attack or an episode of unstable angina severe enough to require hospitalization.

Who Was Enrolled

Patients had to meet all of these criteria:

• Hospitalized for ACS (myocardial infarction or unstable angina) within the previous 1 to 12 months
• LDL cholesterol ≥70 mg/dL, non-HDL cholesterol ≥100 mg/dL, or apolipoprotein B ≥80 mg/dL, despite at least 2 weeks of high-intensity statin therapy (atorvastatin 40 to 80 mg or rosuvastatin 20 to 40 mg)
• Age 40 or older

Exclusion criteria included uncontrolled hypertension, severe renal impairment (eGFR <30), active liver disease, and a history of hemorrhagic stroke. Patients already on stable background therapy such as ezetimibe were allowed to continue it. The trial enrolled across 57 countries and more than 1,300 sites, making it one of the largest cardiovascular outcome trials ever run for a lipid-lowering drug.

What Patients Received

Participants were randomized 1:1 to alirocumab or placebo, both given as subcutaneous injections every two weeks, using a blinded dose-adjustment protocol:

• Starting dose: 75 mg every 2 weeks
• Uptitration: if LDL remained ≥50 mg/dL at month 2, the dose increased to 150 mg every 2 weeks
• Downtitration: if LDL dropped below 15 mg/dL on two consecutive measurements, patients were switched to blinded placebo while remaining in the alirocumab arm for analysis, to avoid sustained very-low LDL

This design let investigators target an LDL range rather than simply maximizing dose in everyone. It also means the intention-to-treat effect size is somewhat diluted, since a portion of the "alirocumab arm" was on placebo by the end of the trial (see Limitations below).

What Was Measured

The primary endpoint was a four-component composite of major adverse cardiovascular events (MACE):

1. Death from coronary heart disease
2. Nonfatal myocardial infarction
3. Fatal or nonfatal ischemic stroke
4. Unstable angina requiring hospitalization

This is a standard composite for cardiovascular outcome trials, though the inclusion of hospitalization for unstable angina, which relies more on clinical judgment than an MI or stroke diagnosis does, has drawn some methodological criticism.

Key secondary endpoints, tested in a hierarchical pre-specified order to control for multiple comparisons, included any coronary heart disease event, any cardiovascular event, a composite of all-cause death plus nonfatal MI plus nonfatal ischemic stroke, and all-cause death alone.

What the Trial Found

Primary endpoint

Over a median follow-up of 2.8 years, the primary MACE endpoint occurred in 9.5% of the alirocumab group versus 11.1% of the placebo group:

• Hazard ratio: 0.85 (95% CI 0.78, 0.93)
• P value: <0.001
• Absolute risk reduction: 1.6 percentage points
• Number needed to treat: approximately 63 over 2.8 years (calculated from the absolute risk reduction above, not a separately published figure)

The Kaplan-Meier event curves began separating within the first year and continued to diverge through the end of follow-up.

Individual components

The trial's original results tables report specific rates and hazard ratios for each component; a medical reviewer should confirm the exact percentages and confidence intervals against the primary publication before those numbers are cited elsewhere on this page. Directionally, the composite benefit was driven mainly by fewer nonfatal MIs and ischemic strokes; CHD death alone did not reach statistical significance as an individual endpoint.

All-cause mortality

All-cause death was a pre-specified secondary endpoint. The numerical difference favored alirocumab (3.5% vs. 4.1%, HR 0.85, 95% CI 0.73, 0.98), but because of the hierarchical testing procedure, this comparison did not meet the pre-specified threshold for formal statistical significance: the mortality test only "counts" if every endpoint earlier in the pre-specified sequence is also significant, and one of those intermediate comparisons narrowly missed.

Several post hoc analyses have explored whether the mortality signal is stronger in specific subgroups, such as patients with higher baseline LDL. Post hoc subgroup findings carry less evidentiary weight than the pre-specified primary analysis, and the exact figures from any single subgroup analysis should be verified against the specific publication before being treated as an established result. The safest reading of the trial itself is that alirocumab showed a suggestive, not proven, mortality benefit in this population.

LDL reduction

The trial's reported LDL trajectories showed a large, sustained separation between arms, consistent with the drug's known LDL-lowering mechanism and dose-titration design. Exact month-by-month values shifted as patients were dose-adjusted or switched to blinded placebo, so a reviewer should pull precise figures directly from the primary publication rather than relying on rounded figures in secondary sources.

Safety Profile

Injection-site reactions were more common with alirocumab than placebo. The trial did not find a significant difference between groups in new-onset diabetes, neurocognitive adverse events, hepatic events, or myalgia and rhabdomyolysis.

The neurocognitive finding is worth emphasizing. Because PCSK9 inhibitors can push LDL to levels well below what most people sustain naturally, there were theoretical concerns about brain cholesterol metabolism. The absence of a neurocognitive signal in ODYSSEY OUTCOMES, combined with findings from a dedicated neurocognitive sub-study of evolocumab reported elsewhere, is reassuring, though it does not by itself establish long-term (beyond a few years) cognitive safety at very low LDL.

Limitations the Authors Acknowledged

Trial duration. A median 2.8-year follow-up may not capture longer-term benefits or risks. Whether the benefit persists, and whether any delayed harms emerge, beyond 3 to 4 years is not answered by this trial alone.

Adaptive dosing complicates interpretation. The blinded dose-switching protocol was clinically sensible but means a portion of the "alirocumab arm" was actually receiving placebo by the end of the trial, which would tend to understate the drug's true effect in an intention-to-treat analysis.

Population specificity. ODYSSEY OUTCOMES enrolled only patients with a recent ACS. Extending these results to primary prevention or to stable coronary disease without a recent event requires caution, even though the broader LDL-lowering evidence base is generally consistent across populations.

Subgroup-driven mortality signal. Any suggestion that mortality benefit is concentrated in patients with higher baseline LDL is biologically plausible, since there is more room for LDL lowering to matter, but it is a post hoc observation, not a pre-specified confirmed result.

Cost and access. At launch, alirocumab's US list price was reported in the tens of thousands of dollars annually. The drug's prescribing information includes the cardiovascular risk reduction indication, and pricing and insurance coverage have both changed materially since the trial's publication; a reviewer should confirm current figures before publishing any specific price.

What Changed in Clinical Practice

Before ODYSSEY OUTCOMES, the 2018 AHA/ACC cholesterol guideline already positioned PCSK9 inhibitors as an option for very-high-risk patients not at LDL goal on maximally tolerated statin plus ezetimibe. ODYSSEY OUTCOMES reinforced that recommendation by confirming a MACE benefit in a second PCSK9 inhibitor, alirocumab, supporting the idea of a class effect rather than a molecule-specific one, and by providing outcome data in a very-high-risk group (recent ACS) where absolute benefit tends to be largest. The adaptive dosing model also influenced real-world prescribing, with many clinicians starting at a lower dose and titrating based on LDL response rather than starting everyone at the maximum dose.

PCSK9 inhibitors are now standard options in guidelines from the ACC/AHA and ESC/EAS for patients with atherosclerotic cardiovascular disease who remain above LDL targets despite statin plus ezetimibe.

Does This Trial's Evidence Apply to a Given Patient? A Decision Framework

This trial answers a specific question for a specific population. Use the steps below to sort out whether it is relevant to a particular situation, and what still needs a clinician's judgment rather than a trial statistic.

Step 1: Check the population match.

• Recent ACS (heart attack or hospitalized unstable angina) within the last 1 to 12 months? If not, this trial's data do not directly apply; ask about the evidence base for primary prevention or stable coronary disease instead.
• LDL still ≥70 mg/dL (or non-HDL ≥100, or ApoB ≥80) despite at least 2 weeks on high-intensity statin therapy? If LDL is already at goal on a statin, this trial does not speak to adding a PCSK9 inhibitor.
• Age 40 or older, and no severe kidney disease (eGFR <30), active liver disease, or history of hemorrhagic stroke? Each of these was an exclusion criterion, so the trial has no direct safety data for these groups.

Step 2: Weigh the size of the benefit against the burden.

• Relative benefit: about 15% fewer MACE events over roughly 3 years.
• Absolute benefit: about 1.6 percentage points, meaning roughly 63 similar patients need to be treated for 2.8 years to prevent one MACE event.
• Burden: an injection every two weeks, indefinitely, plus periodic LDL monitoring and dose review.
• Mortality: a favorable trend that did not reach statistical significance in the primary analysis; treat any death-reduction claim as suggestive rather than proven.

Step 3: Know the exceptions that change the calculus.

• Statin-intolerant patients were not the focus of this trial. Alirocumab was tested on top of statin therapy, not in place of it.
• Patients whose ACS happened more than 12 months ago, or who have never had ACS, fall outside the population actually tested here, even though current guidelines extend PCSK9 inhibitor use more broadly based on other evidence.
• Very low achieved LDL (below 15 mg/dL) triggered a dose-hold in the trial; the trial does not directly address sustained ultra-low LDL beyond its own follow-up window.

Step 4: Practical next steps.

• Confirm current LDL on maximum tolerated statin, plus ezetimibe if already in use, before a PCSK9 inhibitor is considered.
• Ask about insurance prior authorization and current cost, since pricing and coverage have changed since this trial's publication.
• Plan a follow-up LDL check roughly two months after starting therapy, consistent with the trial's own titration schedule.
• Discuss with a cardiologist whether the unresolved mortality question changes shared decision-making for a specific person's overall risk.

Bottom Line for Patients

If someone had a heart attack or a severe episode of unstable angina in the past year, and their LDL cholesterol is still 70 mg/dL or higher despite a high-intensity statin, ODYSSEY OUTCOMES showed that adding alirocumab (an injection every two weeks) reduced the chance of another major cardiovascular event by about 15% relative to placebo over roughly three years. The absolute risk reduction was modest, about 1.6 percentage points, but in a population at this level of risk, that reduction can still be clinically meaningful. The drug was generally well tolerated in the trial, including at very low achieved LDL levels, though whether it reduces the risk of death outright is still an open question rather than a settled one.

Frequently asked questions

›What does ODYSSEY OUTCOMES stand for?

ODYSSEY was the name of the alirocumab clinical development program, and OUTCOMES refers to this specific cardiovascular outcomes trial within that program. Its formal title is "Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab."

›How is alirocumab different from evolocumab?

Both are PCSK9 inhibitors that lower LDL cholesterol by blocking the same protein. Alirocumab (Praluent) was studied in ODYSSEY OUTCOMES; evolocumab (Repatha) was studied in the FOURIER trial. Both trials showed cardiovascular event reduction. The two drugs differ in dosing options and injection devices, but they have not been compared head to head in a clinical trial.

›Did ODYSSEY OUTCOMES prove that alirocumab reduces death?

Not definitively. All-cause death was numerically lower with alirocumab (3.5% vs. 4.1%), but this result did not clear the pre-specified statistical threshold required by the trial's hierarchical testing plan. Some post hoc subgroup analyses have suggested a stronger mortality signal in certain patients, but post hoc findings are considered hypothesis-generating rather than confirmatory.

›Who was actually studied in this trial?

Adults 40 or older who had an acute coronary syndrome in the preceding 1 to 12 months and whose LDL remained ≥70 mg/dL (or equivalent non-HDL or ApoB thresholds) despite high-intensity statin therapy. People with severe kidney disease, active liver disease, or a prior hemorrhagic stroke were excluded, so the trial does not directly address safety in those groups.

›Is it safe to lower LDL below 25 mg/dL?

In this trial, patients whose LDL dropped below 15 mg/dL on two consecutive checks were switched to blinded placebo as a precaution. Over the trial's follow-up, there was no increase in neurocognitive events, liver problems, or other serious harms at very low LDL. Longer-term safety data beyond a few years at extremely low LDL are still limited.

›Can alirocumab replace a statin?

No. ODYSSEY OUTCOMES tested alirocumab on top of a statin, not as a substitute for one. Guidelines generally call for maximizing statin therapy first, adding ezetimibe if needed, and considering a PCSK9 inhibitor as a later step, with an exception for patients who are truly statin-intolerant.

›How long do you need to take alirocumab to see a benefit?

In the trial, the event curves for the two groups began separating within the first year and continued to diverge through the 2.8-year median follow-up. Guidelines generally support continuing therapy for as long as a patient remains at elevated cardiovascular risk, which for most post-ACS patients is indefinitely.

›Did this trial change treatment guidelines?

It reinforced recommendations already emerging in the 2018 AHA/ACC cholesterol guideline and later ESC/EAS guidance supporting PCSK9 inhibitor use in very-high-risk patients with atherosclerotic cardiovascular disease who remain above their LDL target on maximally tolerated statin plus ezetimibe.

References

1. Schwartz GG, Steg PG, Szarek M, et al. Alirocumab and cardiovascular outcomes after acute coronary syndrome. N Engl J Med. 2018;379(22):2097-2107. PubMed
2. Sabatine MS, Giugliano RP, Keech AC, et al. Evolocumab and clinical outcomes in patients with cardiovascular disease. N Engl J Med. 2017;376(18):1713-1722. PubMed
3. Praluent (alirocumab) prescribing information. US Food and Drug Administration.
4. Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of blood cholesterol. Circulation. 2019;139(25):e1082-e1143. PubMed
5. A separate analysis of total (recurrent) nonfatal cardiovascular and fatal events from the ODYSSEY OUTCOMES trial has been reported elsewhere; exact figures should be confirmed against a verified source before citing any LDL-based mortality subgroup figure.
6. An additional LDL-lowering meta-analysis was previously cited here; the bibliographic details could not be confirmed and the reference has been removed pending verification.

Note for Medical Reviewer (remove before publication)

The following items in this draft rely on figures or citation pairings from the prior version of this page that could not be independently re-verified during this rewrite and should be checked before this page goes live:

• Exact per-component rates and hazard ratios for CHD death, nonfatal MI, ischemic stroke, and unstable angina hospitalization, against the primary publication (PMID 30403574).
• The claimed post hoc subgroup mortality figures (previously stated as HR 0.71, 95% CI 0.56 to 0.90, in patients with baseline LDL ≥100 mg/dL) and which publication actually reports them; PMID 31116920 as linked concerns total event counts rather than a mortality subgroup analysis, so that pairing needs confirmation or correction.
• Reference 7 (PMID 30735837): the previous draft attributed this link to the 2015 Lancet Cholesterol Treatment Trialists' Collaboration meta-analysis, but the PMID does not fall in the expected range for a 2015 publication. Confirm what this record actually is, or remove the citation and the claim it supported.
• Exact month-4 LDL values and dose-distribution percentages (75 mg vs. 150 mg vs. blinded placebo), and current US pricing and access information for alirocumab, both of which change over time and were stated as specific figures in the prior draft.