Baloxavir Marboxil side effects: what 2,286 FDA adverse event reports show

Baloxavir Marboxil · Xofluza · 37 reaction terms · 1,816 drug–reaction co-reports · data 2026-09-14

Drug class

Influenza virus polymerase acidic (pa) endonuclease inhibitor

FDA label, Indications wording

Brand names

Xofluza

openFDA label

Who reports

2,286 reports · 53% serious · 136 with death outcome · 54% female

openFDA FAERS counts, all years, deduplication not applied

Used for

XOFLUZA is an influenza virus polymerase acidic (PA) endonuclease inhibitor indicated for: Treatment of acute uncomplicated influenza in patients 5 years of age and older who have been symptomatic for no more than 48 hours and who are otherwise healthy or at high risk of developing influenza-related complications .

FDA label, Indications and Usage

What it is

Baloxavir marboxil is an influenza virus PA endonuclease inhibitor. The active component of XOFLUZA is baloxavir marboxil.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 24 strongest signals

Labeled adverse reaction 6Likely indication confounding 1Reporting / coding artifact 5Lab value / disease marker 1Not in label — unassessed 11

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 13 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Intentional product use issue	283	29.4 26.4–32.8ROR 33.4 · χ² 7,747 / p <1e-300	29.3 EB05 26.5 · IC025 +4.6 3/3 methods agree	Reporting / coding artifact	serious PRR 0.7 · 78% consumer	no trial data cached
No adverse event	546	28.1 26.1–30.3ROR 36.6 · χ² 14,341 / p <1e-300	28.0 EB05 26.1 · IC025 +4.6 3/3 methods agree	Reporting / coding artifact	serious PRR 0.9	no trial data cached
Product packaging quantity issue	31	26.0 18.3–36.8ROR 26.3 · χ² 717 / p 3e-158	25.5 EB05 18.8 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	–	no trial data cached
Erythema multiforme	17	16.6 10.4–26.7ROR 16.8 · χ² 234 / p 4e-53	16.0 EB05 10.1 · IC025 +2.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 18.7	no trial data cached
Melaena (black stool)	30	12.4 8.7–17.7ROR 12.6 · χ² 303 / p 3e-68	11.9 EB05 8.5 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 13.3 · 90% clinician	no trial data cached
Drug eruption	18	9.3 5.9–14.8ROR 9.4 · χ² 125 / p 2e-29	8.1 EB05 5.2 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious PRR 11.7	no trial data cached
Altered state of consciousness	20	8.5 5.5–13.1ROR 8.5 · χ² 124 / p 4e-29	7.4 EB05 5.0 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious PRR 9.3 · ♀ 30% (drug 54%) · 95% clinician	no trial data cached
Prescribed underdose	18	8.2 5.2–13.0ROR 8.3 · χ² 107 / p 2e-25	7.1 EB05 4.6 · IC025 +2.0 3/3 methods agree	Not in label — unassessed	serious PRR 15.3	no trial data cached
Abnormal behaviour	30	6.9 4.8–9.8ROR 6.9 · χ² 145 / p 1e-33	6.3 EB05 4.6 · IC025 +2.0 3/3 methods agree	Not in label — unassessed	serious PRR 8.9 · ♀ 24% (drug 54%) · 90% clinician	no trial data cached
Anaphylactic shock	19	6.8 4.3–10.6ROR 6.8 · χ² 88 / p 4e-21	5.9 EB05 4.0 · IC025 +1.8 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 7.4	no trial data cached
Anaphylactic reaction (severe allergic reaction)	40	6.6 4.9–9.0ROR 6.7 · χ² 186 / p 1e-42	6.2 EB05 4.7 · IC025 +2.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 7.2 · 92% clinician	no trial data cached
Delirium	22	5.8 3.8–8.8ROR 5.8 · χ² 83 / p 5e-20	5.2 EB05 3.6 · IC025 +1.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 6.1	no trial data cached
Rhabdomyolysis (muscle breakdown)	26	5.7 3.9–8.3ROR 5.7 · χ² 96 / p 5e-23	5.2 EB05 3.7 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.2 · ♀ 16% (drug 54%) · 100% clinician	no trial data cached
Hepatic function abnormal	23	5.7 3.8–8.5ROR 5.7 · χ² 84 / p 3e-20	5.1 EB05 3.6 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.4 · 100% clinician	no trial data cached
Influenza	60	4.9 3.8–6.3ROR 5.0 · χ² 183 / p 6e-42	4.7 EB05 3.8 · IC025 +1.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 5.0	no trial data cached
Feeding disorder	10	4.6 2.5–8.5ROR 4.6 · χ² 24 / p 4e-7	3.9 EB05 2.3 · IC025 +0.9 3/3 methods agree	Not in label — unassessed	serious PRR 3.5	no trial data cached
Off label use (used outside approved label)	426	4.5 4.1–4.9ROR 5.3 · χ² 1,195 / p 4e-262	4.5 EB05 4.1 · IC025 +2.0 3/3 methods agree	Reporting / coding artifact	serious PRR 0.8	no trial data cached
Encephalopathy	12	4.5 2.5–7.9ROR 4.5 · χ² 29 / p 4e-8	3.9 EB05 2.4 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious PRR 4.9	no trial data cached
Liver injury	11	4.1 2.3–7.5ROR 4.2 · χ² 23 / p 7e-7	3.6 EB05 2.2 · IC025 +0.8 3/3 methods agree	Not in label — unassessed	serious PRR 4.7	no trial data cached
Haematochezia (blood in stool)	24	4.0 2.7–5.9ROR 4.0 · χ² 51 / p 6e-13	3.7 EB05 2.6 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 4.4 · 96% clinician	no trial data cached
Depressed level of consciousness	17	3.9 2.4–6.3ROR 3.9 · χ² 34 / p 2e-9	3.6 EB05 2.4 · IC025 +1.0 3/3 methods agree	Not in label — unassessed	serious PRR 4.1	no trial data cached
Product prescribing error	10	3.8 2.1–7.1ROR 3.9 · χ² 18 / p 9e-6	3.4 EB05 2.0 · IC025 +0.7	Reporting / coding artifact	serious PRR 0.9	no trial data cached
Hallucination (hallucinations)	30	3.6 2.6–5.2ROR 3.7 · χ² 55 / p 5e-14	3.5 EB05 2.6 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.1	no trial data cached
International normalised ratio increased	11	3.5 1.9–6.3ROR 3.5 · χ² 17 / p 2e-5	3.1 EB05 1.9 · IC025 +0.6	Lab value / disease marker	serious PRR 4.2	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
No adverse event	546	28.1 26.1–30.3ROR 36.6 · χ² 14,341 / p <1e-300	28.0 EB05 26.1 · IC025 +4.6 3/3 methods agree	Reporting / coding artifact	serious PRR 0.9	no trial data cached
Off label use (used outside approved label)	426	4.5 4.1–4.9ROR 5.3 · χ² 1,195 / p 4e-262	4.5 EB05 4.1 · IC025 +2.0 3/3 methods agree	Reporting / coding artifact	serious PRR 0.8	no trial data cached
Intentional product use issue	283	29.4 26.4–32.8ROR 33.4 · χ² 7,747 / p <1e-300	29.3 EB05 26.5 · IC025 +4.6 3/3 methods agree	Reporting / coding artifact	serious PRR 0.7 · 78% consumer	no trial data cached
Influenza	60	4.9 3.8–6.3ROR 5.0 · χ² 183 / p 6e-42	4.7 EB05 3.8 · IC025 +1.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 5.0	no trial data cached
Anaphylactic reaction (severe allergic reaction)	40	6.6 4.9–9.0ROR 6.7 · χ² 186 / p 1e-42	6.2 EB05 4.7 · IC025 +2.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 7.2 · 92% clinician	no trial data cached
Product packaging quantity issue	31	26.0 18.3–36.8ROR 26.3 · χ² 717 / p 3e-158	25.5 EB05 18.8 · IC025 +3.6 3/3 methods agree	Reporting / coding artifact	–	no trial data cached
Hallucination (hallucinations)	30	3.6 2.6–5.2ROR 3.7 · χ² 55 / p 5e-14	3.5 EB05 2.6 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.1	no trial data cached
Abnormal behaviour	30	6.9 4.8–9.8ROR 6.9 · χ² 145 / p 1e-33	6.3 EB05 4.6 · IC025 +2.0 3/3 methods agree	Not in label — unassessed	serious PRR 8.9 · ♀ 24% (drug 54%) · 90% clinician	no trial data cached
Melaena (black stool)	30	12.4 8.7–17.7ROR 12.6 · χ² 303 / p 3e-68	11.9 EB05 8.5 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 13.3 · 90% clinician	no trial data cached
Rhabdomyolysis (muscle breakdown)	26	5.7 3.9–8.3ROR 5.7 · χ² 96 / p 5e-23	5.2 EB05 3.7 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.2 · ♀ 16% (drug 54%) · 100% clinician	no trial data cached
Haematochezia (blood in stool)	24	4.0 2.7–5.9ROR 4.0 · χ² 51 / p 6e-13	3.7 EB05 2.6 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 4.4 · 96% clinician	no trial data cached
Hepatic function abnormal	23	5.7 3.8–8.5ROR 5.7 · χ² 84 / p 3e-20	5.1 EB05 3.6 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 6.4 · 100% clinician	no trial data cached
Delirium	22	5.8 3.8–8.8ROR 5.8 · χ² 83 / p 5e-20	5.2 EB05 3.6 · IC025 +1.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 6.1	no trial data cached
Altered state of consciousness	20	8.5 5.5–13.1ROR 8.5 · χ² 124 / p 4e-29	7.4 EB05 5.0 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious PRR 9.3 · ♀ 30% (drug 54%) · 95% clinician	no trial data cached
Anaphylactic shock	19	6.8 4.3–10.6ROR 6.8 · χ² 88 / p 4e-21	5.9 EB05 4.0 · IC025 +1.8 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 7.4	no trial data cached

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Melaena — n=30, PRR 12.4
Altered state of consciousness — n=20, PRR 8.5
Abnormal behaviour — n=30, PRR 6.9
Rhabdomyolysis — n=26, PRR 5.7
Hepatic function abnormal — n=23, PRR 5.7

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Baloxavir Marboxil?

In FDA FAERS, the most frequently co-reported reaction terms for Baloxavir Marboxil are influenza, anaphylactic reaction, hallucination, abnormal behaviour, melaena, rhabdomyolysis. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Baloxavir Marboxil have an FDA boxed warning?

No. The FDA label retrieved for Baloxavir Marboxil has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Baloxavir Marboxil causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID b58b2899-4d22-41e1-8f0c-bdead8917694, effective 20260424; matched on openfda.generic_name.exact:"BALOXAVIR MARBOXIL")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 37 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.