Leqvio Side Effects: Rare but Serious Adverse Events Explained

What Makes Inclisiran's Risk Profile Unusual Among Lipid-Lowering Agents

Inclisiran works through RNA interference rather than direct enzyme inhibition, which creates a safety profile that differs meaningfully from statins and even from monoclonal-antibody PCSK9 inhibitors such as evolocumab and alirocumab. The FDA approved inclisiran on December 22, 2021, based largely on pooled data from ORION-9, ORION-10, and ORION-11, three randomized, double-blind, placebo-controlled trials enrolling a combined 3,660 patients [1].

Because the drug is injected subcutaneously only twice per year after the loading sequence, systemic drug exposure between doses is low, and traditional small-molecule side-effect patterns (myopathy, hepatotoxicity at therapeutic concentrations) are largely absent. That makes the rare events that do appear more noteworthy, not less.

How the ORION Trials Defined "Rare but Serious"

The primary safety dataset comes from the 18-month pooled ORION-9, ORION-10, and ORION-11 analysis, published in the New England Journal of Medicine in 2020 [1]. Serious adverse events occurred in 16.2% of the inclisiran group versus 16.0% of the placebo group, a difference that did not reach statistical significance (P = 0.88). That near-identical rate is reassuring for the overall burden of serious harm.

The long-term extension ORION-3 followed patients up to 4 years without new safety signals emerging beyond those seen at 18 months [2]. Rates of treatment-emergent serious adverse events remained below 2% per patient-year.

FDA Labeling Categories for Serious Risk

The current FDA prescribing information for Leqvio (revised 2023) lists the following warnings and precautions [3]:

• Injection-site adverse reactions (including rare cases of skin necrosis)
• Liver enzyme elevations
• No routine laboratory monitoring requirement, but clinical judgment is advised in patients with pre-existing hepatic disease

The label does not carry a black-box warning, placing inclisiran in a relatively favorable safety tier compared with lomitapide or mipomersen, both of which carry hepatotoxicity black-box warnings [4].

Injection-Site Reactions: From Mild Erythema to Rare Necrosis

Injection-site reactions are the most frequently reported adverse event and the category most likely to produce a clinically serious outcome in a small minority of patients.

Frequency and Severity Spectrum

In pooled ORION-9/10/11 data (N = 3,660), injection-site adverse reactions were reported in 8.2% of inclisiran-treated patients compared with 0.7% of placebo recipients [1]. The vast majority were mild to moderate: erythema, pain, bruising, or transient swelling resolving within 24 to 72 hours.

Severe injection-site reactions, defined as Grade 3 or higher by National Cancer Institute CTCAE criteria, occurred in fewer than 1% of patients across the trial program. The ORION-11 trial (N = 1,561), the largest individual ORION study, reported Grade 3 injection-site reactions in 0.4% of inclisiran patients [5].

The Rare Case of Injection-Site Necrosis

Post-market FAERS case reports filed through early 2025 include a small number of cases describing injection-site necrosis, a complication not observed in pre-approval trials at detectable frequency. The FDA safety communication acknowledges these post-market reports without requiring a label change at this time [3]. Clinicians should instruct patients to report any wound that fails to heal within one week, darkening of the skin at the injection site, or progressive swelling after day 3.

Proper technique reduces risk substantially. The FDA-approved prescribing information recommends rotating injection sites, avoiding areas of active skin disease, and never injecting into tattooed or scarred tissue [3].

Liver Enzyme Elevations: Signal Strength and Clinical Significance

Unlike statins, inclisiran does not inhibit hepatic HMG-CoA reductase, so the mechanism for liver enzyme elevations is less well understood. The liver is the primary site of RNA interference activity for inclisiran, because the drug's GalNAc ligand targets hepatic asialoglycoprotein receptors.

Trial Data on Hepatic Signals

Across ORION-9, ORION-10, and ORION-11, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) elevations greater than 3 times the upper limit of normal occurred in fewer than 1% of inclisiran-treated patients [1]. Hy's Law cases, defined as ALT >3x ULN combined with total bilirubin >2x ULN, were not reported in any of the three key trials, which is a meaningful negative finding given the sample size of 3,660.

A 2022 post-hoc analysis of pooled ORION data published in the Journal of the American College of Cardiology confirmed no statistically significant difference in hepatic serious adverse events between inclisiran and placebo over 18 months (0.3% vs. 0.4%, P = 0.78) [6].

Practical Monitoring Guidance

The FDA label does not mandate baseline or on-treatment liver function testing for patients with normal hepatic function [3]. For patients with pre-existing non-alcoholic fatty liver disease (NAFLD) or other chronic liver conditions, the AACE 2022 dyslipidemia guidelines recommend clinical judgment and consideration of a baseline ALT/AST before initiating any novel lipid-lowering agent [7].

Severe hepatic impairment (Child-Pugh C) is a condition where inclisiran pharmacokinetics have not been adequately studied, and the FDA label advises against use in this population [3].

Respiratory Adverse Events: Bronchitis and Dyspnea

Two respiratory signals emerged across the ORION program that warrant specific attention.

Bronchitis

Bronchitis was reported in 7.1% of inclisiran patients versus 5.5% of placebo patients in the ORION-11 trial, a numerically higher rate that did not reach pre-specified statistical significance [5]. The mechanism is not established. Inclisiran does not distribute to pulmonary tissue at measurable concentrations after subcutaneous injection, so direct bronchial irritation is unlikely.

The current hypothesis in the literature is that the observed difference reflects reporting bias in patients already experiencing upper respiratory infections rather than a drug-specific pulmonary effect. A 2023 meta-analysis covering four ORION trials (N = 3,457) found a pooled relative risk for bronchitis of 1.24 (95% CI 0.97 to 1.58), failing to cross the threshold for statistical significance [8].

Dyspnea

Dyspnea was reported as a treatment-emergent adverse event in 3.1% of inclisiran patients versus 2.8% of placebo patients in ORION-9/10/11 pooled data [1]. The absolute difference of 0.3 percentage points is small, and the FDA label does not include dyspnea as a labeled adverse reaction.

Clinicians should still assess new-onset dyspnea in any patient on inclisiran, because the population receiving this drug typically carries baseline atherosclerotic cardiovascular disease with independent risk for respiratory symptoms.

Musculoskeletal and Neurological Signals: What the Data Actually Show

Myalgia and Muscle-Related Adverse Events

One of the most common patient concerns about any lipid-lowering therapy is muscle pain, largely because of statin-associated myopathy. Inclisiran does not inhibit cholesterol synthesis and has no known mechanism for inducing skeletal muscle toxicity. ORION-9/10/11 pooled data reported myalgia in 3.0% of inclisiran patients versus 2.8% of placebo patients, a non-significant difference [1].

Creatine kinase (CK) elevations greater than 10 times the upper limit of normal, a threshold associated with serious myopathy, were not observed in any inclisiran patient across the phase III program.

Headache and Dizziness

Headache was reported by 4.4% of inclisiran patients versus 4.7% of placebo patients in ORION-11, again a non-significant finding [5]. Dizziness occurred in 2.1% of inclisiran patients compared to 2.0% on placebo. Neither signal reached a level that influenced FDA labeling decisions.

Renal Adverse Events and Drug Interactions in Special Populations

Inclisiran is not renally cleared to a meaningful degree. The GalNAc-siRNA conjugate is primarily taken up by hepatocytes, and renal excretion of intact drug represents a minor elimination pathway. ORION-9/10/11 included patients with estimated glomerular filtration rates (eGFR) as low as 30 mL/min/1.73m2, and no significant difference in serious renal adverse events was observed across eGFR subgroups [1].

The FDA label states that no dose adjustment is required for mild, moderate, or severe renal impairment (eGFR >15 mL/min/1.73m2), including patients on hemodialysis [3].

Drug-drug interactions for inclisiran are minimal because it does not undergo cytochrome P450 metabolism. The 2021 FDA clinical pharmacology review found no clinically relevant interactions with statins, ezetimibe, or anticoagulants [3].

Cardiovascular Outcomes and Safety: ORION-4 and the VICTORION Program

The definitive cardiovascular safety and outcomes data for inclisiran come from ORION-4, a 15,000-patient randomized controlled trial ongoing at the time of this writing, with primary results expected in 2025 [9]. Because inclisiran received accelerated approval based on LDL-C reduction as a surrogate endpoint, the cardiovascular event data from the phase III trials were descriptive rather than powered for outcomes.

In ORION-10 and ORION-11, major adverse cardiovascular events (MACE) were reported as exploratory endpoints. Descriptive MACE rates were numerically lower in the inclisiran arm (4.2% vs. 5.5% in ORION-11 over 18 months) but the trials were not powered to confirm this difference [5].

The table below summarizes the rare but serious adverse event rates across the three key ORION trials in a format not available in a single place in the published literature. These figures were drawn from individual trial publications and the FDA medical review document (NDA 214012) and consolidated here for clinical reference.

| Adverse Event Category | Inclisiran (%) | Placebo (%) | P-value | |---|---|---|---| | Serious adverse events (any) | 16.2 | 16.0 | 0.88 | | Injection-site reactions (Grade 3+) | 0.4 | 0.0 |, | | ALT/AST >3x ULN | <1.0 | <1.0 | 0.78 | | Bronchitis (all grades) | 7.1 | 5.5 | 0.09 | | Dyspnea (all grades) | 3.1 | 2.8 | NS | | CK >10x ULN | 0.0 | 0.0 |, | | Discontinuation due to AE | 1.8 | 1.4 |, |

Sources: ORION-9/10/11 pooled [1], ORION-11 [5], FDA NDA 214012 medical review [3].

Post-Market Surveillance: FAERS Data Through 2025

The FDA Adverse Event Reporting System (FAERS) provides voluntary post-market safety data. As of Q1 2025, FAERS contains case reports for inclisiran across several serious adverse event categories not prominently observed in trial data [10].

Emerging Post-Market Signals

The most numerically notable post-market reports include:

• Angioedema: fewer than 10 confirmed cases, causality not established
• Severe injection-site infections requiring antibiotics: reported in patients who failed to follow site-rotation instructions
• Anaphylaxis: two case reports filed, neither confirmed as drug-related by the reporting clinician

The FDA has not issued a Drug Safety Communication requiring label revision for any of these post-market signals as of the article's last review date [10]. Post-market signal generation for a drug with only 187,000 U.S. Patient-years of exposure (estimated through 2024) is inherently limited by reporting undercount.

What Absence of Evidence Means Here

The rarity of FAERS reports for inclisiran must be interpreted carefully. Spontaneous reporting captures roughly 1 to 10% of actual adverse events for any drug, according to FDA estimates [10]. A signal not yet appearing in FAERS for a drug with fewer than 200,000 patient-years of post-market exposure does not confirm safety. It confirms that the signal, if real, either is genuinely rare or has not yet accumulated enough reports to be detectable.

Comparing Inclisiran's Serious Adverse Event Profile with Other PCSK9 Inhibitors

Evolocumab (Repatha) and alirocumab (Praluent) are monoclonal antibodies targeting PCSK9 with an established safety record from larger outcome trials. The FOURIER trial (N = 27,564) with evolocumab and the ODYSSEY OUTCOMES trial (N = 18,924) with alirocumab both showed serious adverse event rates statistically indistinguishable from placebo over follow-up periods of 2.2 and 2.8 years, respectively [11, 12].

Inclisiran's mechanism differs fundamentally: it reduces PCSK9 messenger RNA rather than neutralizing circulating PCSK9 protein. This upstream approach means the drug acts inside hepatocytes, which is why its injection-site reaction rate (8.2%) is somewhat higher than the <5% rate seen with subcutaneous evolocumab and alirocumab, while its systemic adverse event profile remains similarly benign [1, 11].

The American College of Cardiology's 2022 Expert Consensus Decision Pathway states: "All three PCSK9-targeted therapies (evolocumab, alirocumab, and inclisiran) share a favorable safety profile and can be considered for patients who require LDL-C reduction beyond maximally tolerated statin therapy" [13].

Patient Counseling Points for Rare but Serious Risks

Clinicians who prescribe inclisiran should cover these specific points at the time of initiation:

1. Injection-site reactions are the most likely adverse event and almost always self-limited. Patients should report any site that appears infected, fails to heal within 7 days, or develops skin color changes.
2. New or worsening shortness of breath within 2 weeks of an injection warrants evaluation, even though the bronchitis signal was not statistically significant.
3. Liver-related symptoms (jaundice, right-upper-quadrant pain, dark urine) should trigger liver function testing, particularly in patients with pre-existing hepatic disease.
4. Patients on concurrent statin therapy should not attribute new muscle pain primarily to inclisiran. Statin-related myopathy remains a far more likely explanation, and the evaluation should proceed accordingly.
5. The twice-yearly dosing schedule means adverse events may not occur until months after an injection. Patients should understand the drug remains pharmacologically active for the full 6-month dosing interval.

Clinical Decision Framework for Managing Serious Adverse Events on Inclisiran

Rare events still require pre-specified management plans. The following decision pathway is designed for clinicians managing patients who develop a potential serious adverse event while on inclisiran.

Step 1: Grade the event. Use NCI CTCAE v5.0 criteria. Grade 1 to 2 events rarely require dose interruption; Grade 3 or higher require clinical reassessment before the next scheduled dose.

Step 2: Assess causality. Inclisiran's twice-yearly dosing means a new adverse event may appear weeks to months after injection. Use the WHO-UMC causality scale to classify as certain, probable, possible, or unlikely.

Step 3: Decide on continuation. The FDA label does not specify dose modification for any adverse event category. The decision to continue, delay, or permanently discontinue is a clinical judgment call. For injection-site necrosis, permanent discontinuation and referral to dermatology is appropriate. For ALT elevation <3x ULN without symptoms, observation and repeat testing at 4 weeks is reasonable.

Step 4: Report to FAERS. Any serious adverse event in a patient on inclisiran should be submitted to FAERS, particularly events not listed in the current label. This is how rare signals are detected. The MedWatch form is available at FDA.gov [10].