Fostamatinib side effects: what 7,695 FDA adverse event reports show

Fostamatinib · Tavalisse · 132 reaction terms · 9,556 drug–reaction co-reports · data 2026-09-14

Drug class

Kinase inhibitor

FDA label, Indications wording

Brand names

Tavalisse

openFDA label

Who reports

7,695 reports · 32% serious · 463 with death outcome · 61% female

openFDA FAERS counts, all years, deduplication not applied

Used for

TAVALISSE is indicated for the treatment of thrombocytopenia in adult patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment. TAVALISSE is a kinase inhibitor indicated for the treatment of thrombocytopenia in adult patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment.

FDA label, Indications and Usage

What it is

Fostamatinib is a tyrosine kinase inhibitor. TAVALISSE is formulated with the disodium hexahydrate salt of fostamatinib, a phosphate prodrug that converts to its pharmacologically active metabolite, R406, in vivo .

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 40 strongest signals

Labeled adverse reaction 2Labeled (related wording) 4Reporting / coding artifact 12Lab value / disease marker 6Not in label — unassessed 16

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.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
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. 92 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
Product prescribing issue	313	42.6 38.1–47.5ROR 44.3 · χ² 12,475 / p <1e-300	41.8 EB05 38.1 · IC025 +5.1 3/3 methods agree	Reporting / coding artifact	serious PRR 50.2 · 88% consumer	no trial data cached
Platelet count increased	187	39.6 34.3–45.6ROR 40.5 · χ² 6,893 / p <1e-300	38.9 EB05 34.4 · IC025 +4.9 3/3 methods agree	Lab value / disease marker	serious PRR 22.6 · 86% consumer	no trial data cached
Platelet count decreased	996	25.7 24.3–27.3ROR 29.4 · χ² 23,529 / p <1e-300	25.5 EB05 24.2 · IC025 +4.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 24.0 · 86% consumer	no trial data cached
Petechiae	41	10.8 7.9–14.6ROR 10.8 · χ² 353 / p 5e-79	10.3 EB05 7.7 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	serious PRR 12.1 · 73% consumer	no trial data cached
Product dose omission issue	1,008	9.7 9.1–10.3ROR 11.0 · χ² 7,915 / p <1e-300	9.6 EB05 9.1 · IC025 +3.2 3/3 methods agree	Reporting / coding artifact	serious PRR 11.6 · 95% consumer	no trial data cached
Hospitalisation	484	8.7 8.0–9.5ROR 9.2 · χ² 3,295 / p <1e-300	8.6 EB05 8.0 · IC025 +3.0 3/3 methods agree	Reporting / coding artifact	serious PRR 16.2 · 87% consumer	no trial data cached
Blood pressure increased	379	6.8 6.1–7.5ROR 7.1 · χ² 1,861 / p <1e-300	6.7 EB05 6.1 · IC025 +2.6 3/3 methods agree	Labeled (related wording) related wording	serious PRR 2.7 · 90% consumer	no trial data cached
Transfusion	21	5.5 3.6–8.4ROR 5.5 · χ² 72 / p 1e-17	4.9 EB05 3.4 · IC025 +1.6 3/3 methods agree	Not in label — unassessed	serious PRR 5.0 · 86% consumer	no trial data cached
Blood pressure abnormal	38	5.2 3.8–7.2ROR 5.3 · χ² 126 / p 2e-29	4.9 EB05 3.8 · IC025 +1.8 3/3 methods agree	Lab value / disease marker	serious PRR 2.2 · 92% consumer	no trial data cached
Laboratory test abnormal	50	4.6 3.5–6.1ROR 4.7 · χ² 139 / p 3e-32	4.4 EB05 3.5 · IC025 +1.7 3/3 methods agree	Reporting / coding artifact	serious PRR 5.2 · 94% consumer	no trial data cached
Product dose omission	111	4.6 3.8–5.5ROR 4.6 · χ² 307 / p 5e-69	4.5 EB05 3.8 · IC025 +1.9 3/3 methods agree	Reporting / coding artifact	serious PRR 3.4 · 88% consumer	no trial data cached
Diarrhoea (diarrhea)	1,053	4.5 4.2–4.7ROR 5.0 · χ² 2,915 / p <1e-300	4.5 EB05 4.2 · IC025 +2.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.0 · 86% consumer	no trial data cached
Hospice care	16	4.4 2.7–7.2ROR 4.4 · χ² 39 / p 2e-10	4.0 EB05 2.6 · IC025 +1.2 3/3 methods agree	Not in label — unassessed	–	no trial data cached
Gingival bleeding	22	4.4 2.9–6.7ROR 4.4 · χ² 54 / p 9e-14	4.0 EB05 2.8 · IC025 +1.3 3/3 methods agree	Not in label — unassessed	serious PRR 6.5	no trial data cached
Contusion	148	4.2 3.6–4.9ROR 4.3 · χ² 359 / p 3e-80	4.1 EB05 3.6 · IC025 +1.8 3/3 methods agree	Not in label — unassessed	serious PRR 2.8 · 85% consumer	no trial data cached
Emotional disorder	47	4.1 3.1–5.5ROR 4.2 · χ² 109 / p 1e-25	4.0 EB05 3.1 · IC025 +1.5 3/3 methods agree	Not in label — unassessed	serious PRR 3.2 · 96% consumer	no trial data cached
Epistaxis (nosebleed)	111	4.0 3.4–4.9ROR 4.1 · χ² 251 / p 6e-57	4.0 EB05 3.4 · IC025 +1.7 3/3 methods agree	Not in label — unassessed	serious PRR 5.6 · 80% consumer	no trial data cached
Liver function test increased	31	4.0 2.8–5.6ROR 4.0 · χ² 66 / p 3e-16	3.8 EB05 2.8 · IC025 +1.3 3/3 methods agree	Labeled (related wording) related wording	serious PRR 1.8 · 87% consumer	no trial data cached
Frequent bowel movements	39	4.0 2.9–5.4ROR 4.0 · χ² 83 / p 4e-20	3.8 EB05 2.9 · IC025 +1.4 3/3 methods agree	Not in label — unassessed	serious PRR 0.9 · 82% consumer	no trial data cached
Hepatic enzyme increased	78	3.1 2.5–3.9ROR 3.2 · χ² 111 / p 3e-26	3.1 EB05 2.6 · IC025 +1.3 3/3 methods agree	Labeled (related wording) related wording	serious PRR 1.8 · 81% consumer	no trial data cached
Adverse event	104	3.1 2.5–3.7ROR 3.1 · χ² 144 / p 2e-33	3.0 EB05 2.6 · IC025 +1.3 3/3 methods agree	Reporting / coding artifact	serious PRR 2.1	no trial data cached
Flatulence (gas)	60	2.9 2.2–3.7ROR 2.9 · χ² 72 / p 9e-18	2.8 EB05 2.3 · IC025 +1.1 3/3 methods agree	Not in label — unassessed	serious PRR 2.0 · 93% consumer	no trial data cached
Blood iron decreased	12	2.8 1.6–4.9ROR 2.8 · χ² 12 / p 3e-4	2.6 EB05 1.6 · IC025 +0.4	Lab value / disease marker	serious PRR 1.1	no trial data cached
Hepatomegaly	10	2.8 1.5–5.1ROR 2.8 · χ² 10 / p 0.001	2.5 EB05 1.5 · IC025 +0.3	Not in label — unassessed	serious PRR 3.8	no trial data cached
Unevaluable event	76	2.7 2.2–3.4ROR 2.8 · χ² 82 / p 6e-20	2.7 EB05 2.2 · IC025 +1.1 3/3 methods agree	Reporting / coding artifact	serious PRR 2.4 · 95% consumer	no trial data cached
Therapy non-responder	44	2.7 2.0–3.6ROR 2.7 · χ² 45 / p 9e-12	2.6 EB05 2.0 · IC025 +0.9 3/3 methods agree	Reporting / coding artifact	serious PRR 4.6	no trial data cached
Off label use (used outside approved label)	840	2.6 2.5–2.8ROR 2.8 · χ² 890 / p 9e-196	2.6 EB05 2.5 · IC025 +1.3 3/3 methods agree	Reporting / coding artifact	serious PRR 2.8 · 85% consumer	no trial data cached
Hypertension (high blood pressure)	202	2.6 2.3–3.0ROR 2.6 · χ² 199 / p 2e-45	2.6 EB05 2.3 · IC025 +1.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 1.4 · 81% consumer	no trial data cached
Full blood count abnormal	10	2.6 1.4–4.8ROR 2.6 · χ² 8 / p 0.002	2.4 EB05 1.4 · IC025 +0.2	Lab value / disease marker	serious PRR 3.8	no trial data cached
Intentional product misuse	82	2.6 2.1–3.2ROR 2.6 · χ² 78 / p 6e-19	2.5 EB05 2.1 · IC025 +1.0 3/3 methods agree	Reporting / coding artifact	serious PRR 2.7 · 79% consumer	no trial data cached
Depressed mood	49	2.5 1.9–3.4ROR 2.5 · χ² 44 / p 1e-11	2.5 EB05 2.0 · IC025 +0.8	Not in label — unassessed	serious PRR 1.5 · 96% consumer	no trial data cached
Blood test abnormal	13	2.5 1.5–4.3ROR 2.5 · χ² 10 / p 6e-4	2.4 EB05 1.5 · IC025 +0.3	Reporting / coding artifact	serious PRR 2.2	no trial data cached
Covid-19 pneumonia	11	2.5 1.4–4.6ROR 2.5 · χ² 9 / p 0.002	2.4 EB05 1.4 · IC025 +0.2	Not in label — unassessed	serious PRR 3.8	no trial data cached
Blood count abnormal	14	2.5 1.5–4.2ROR 2.5 · χ² 11 / p 5e-4	2.4 EB05 1.5 · IC025 +0.3	Lab value / disease marker	serious PRR 1.8	no trial data cached
Brain fog	13	2.4 1.4–4.2ROR 2.4 · χ² 10 / p 0.001	2.3 EB05 1.5 · IC025 +0.3	Not in label — unassessed	serious PRR 1.3	no trial data cached
Cholecystectomy	10	2.4 1.3–4.5ROR 2.4 · χ² 7 / p 0.005	2.3 EB05 1.3 · IC025 +0.1	Not in label — unassessed	serious PRR 3.6	no trial data cached
Product use issue	164	2.4 2.1–2.8ROR 2.4 · χ² 132 / p 6e-31	2.4 EB05 2.1 · IC025 +1.0 3/3 methods agree	Reporting / coding artifact	serious PRR 2.0 · 87% consumer	no trial data cached
Internal haemorrhage	10	2.4 1.3–4.4ROR 2.4 · χ² 7 / p 0.005	2.2 EB05 1.3 · IC025 +0.1	Not in label — unassessed	serious PRR 4.0	no trial data cached
Blood potassium increased	14	2.4 1.4–4.0ROR 2.4 · χ² 10 / p 1e-3	2.2 EB05 1.4 · IC025 +0.3	Lab value / disease marker	serious PRR 4.0	no trial data cached
Increased appetite	16	2.3 1.4–3.8ROR 2.3 · χ² 11 / p 5e-4	2.2 EB05 1.5 · IC025 +0.3	Not in label — unassessed	serious PRR 0.7	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
Diarrhoea (diarrhea)	1,053	4.5 4.2–4.7ROR 5.0 · χ² 2,915 / p <1e-300	4.5 EB05 4.2 · IC025 +2.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.0 · 86% consumer	no trial data cached
Product dose omission issue	1,008	9.7 9.1–10.3ROR 11.0 · χ² 7,915 / p <1e-300	9.6 EB05 9.1 · IC025 +3.2 3/3 methods agree	Reporting / coding artifact	serious PRR 11.6 · 95% consumer	no trial data cached
Platelet count decreased	996	25.7 24.3–27.3ROR 29.4 · χ² 23,529 / p <1e-300	25.5 EB05 24.2 · IC025 +4.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 24.0 · 86% consumer	no trial data cached
Off label use (used outside approved label)	840	2.6 2.5–2.8ROR 2.8 · χ² 890 / p 9e-196	2.6 EB05 2.5 · IC025 +1.3 3/3 methods agree	Reporting / coding artifact	serious PRR 2.8 · 85% consumer	no trial data cached
Hospitalisation	484	8.7 8.0–9.5ROR 9.2 · χ² 3,295 / p <1e-300	8.6 EB05 8.0 · IC025 +3.0 3/3 methods agree	Reporting / coding artifact	serious PRR 16.2 · 87% consumer	no trial data cached
Fatigue (tiredness)	396	1.4 1.3–1.5ROR 1.4 · χ² 44 / p 1e-11	1.4 EB05 1.3 · IC025 +0.3	Labeled adverse reaction exact term	serious PRR 0.8 · 91% consumer	no trial data cached
Blood pressure increased	379	6.8 6.1–7.5ROR 7.1 · χ² 1,861 / p <1e-300	6.7 EB05 6.1 · IC025 +2.6 3/3 methods agree	Labeled (related wording) related wording	serious PRR 2.7 · 90% consumer	no trial data cached
Death	336	1.1 1.0–1.2ROR 1.1 · χ² 1 / p 0.132	1.1 EB05 1.0 · IC025 -0.1 PRR-only: not supported by EBGM or IC	Outcome field, not a reaction	serious PRR 1.9	no trial data cached
Product prescribing issue	313	42.6 38.1–47.5ROR 44.3 · χ² 12,475 / p <1e-300	41.8 EB05 38.1 · IC025 +5.1 3/3 methods agree	Reporting / coding artifact	serious PRR 50.2 · 88% consumer	no trial data cached
Hypertension (high blood pressure)	202	2.6 2.3–3.0ROR 2.6 · χ² 199 / p 2e-45	2.6 EB05 2.3 · IC025 +1.1 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 1.4 · 81% consumer	no trial data cached
Platelet count increased	187	39.6 34.3–45.6ROR 40.5 · χ² 6,893 / p <1e-300	38.9 EB05 34.4 · IC025 +4.9 3/3 methods agree	Lab value / disease marker	serious PRR 22.6 · 86% consumer	no trial data cached
Product use issue	164	2.4 2.1–2.8ROR 2.4 · χ² 132 / p 6e-31	2.4 EB05 2.1 · IC025 +1.0 3/3 methods agree	Reporting / coding artifact	serious PRR 2.0 · 87% consumer	no trial data cached
Contusion	148	4.2 3.6–4.9ROR 4.3 · χ² 359 / p 3e-80	4.1 EB05 3.6 · IC025 +1.8 3/3 methods agree	Not in label — unassessed	serious PRR 2.8 · 85% consumer	no trial data cached
Abdominal discomfort	132	2.2 1.8–2.5ROR 2.2 · χ² 81 / p 1e-19	2.1 EB05 1.9 · IC025 +0.8	Not in label — unassessed	serious PRR 1.3 · 89% consumer	no trial data cached
Covid-19	124	1.9 1.6–2.3ROR 1.9 · χ² 53 / p 1e-13	1.9 EB05 1.6 · IC025 +0.6	Not in label — unassessed	serious PRR 2.4 · 88% consumer	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.

Petechiae — n=41, PRR 10.8
Transfusion — n=21, PRR 5.5
Gingival bleeding — n=22, PRR 4.4
Contusion — n=148, PRR 4.2
Emotional disorder — n=47, PRR 4.1
Epistaxis — n=111, PRR 4.0
Frequent bowel movements — n=39, PRR 4.0
Flatulence — n=60, PRR 2.9
Depressed mood — n=49, PRR 2.5

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 Fostamatinib?

In FDA FAERS, the most frequently co-reported reaction terms for Fostamatinib are diarrhoea, platelet count decreased, fatigue, blood pressure increased, hypertension, platelet count increased. 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 Fostamatinib have an FDA boxed warning?

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

Do FAERS signals prove that Fostamatinib 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 21149cc3-049b-43e2-b141-c9499160556c, effective 20251105; matched on openfda.generic_name.exact:"FOSTAMATINIB")
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, 132 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.