Drug · FAERS side-effect profile with label screen
Famciclovir side effects: what 2,752 FDA adverse event reports show
Drug class
Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitor
FDA label (Established Pharmacologic Class) · compare the class
Who reports
2,752 reports · 70% serious · 274 with death outcome · 60% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Famciclovir tablet, a prodrug of penciclovir, is a deoxynucleoside analog DNA polymerase inhibitor indicated for: Immunocompetent Adult Patients ( 1.1 ) • Herpes labialis (cold sores) o Treatment of recurrent episodes • Genital herpes o Treatment of re.
FDA label, Indications and Usage
What it is
The active ingredient in famciclovir tablets is famciclovir, USP, an orally administered prodrug of the antiviral agent penciclovir.
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) 4Likely indication confounding 1Reporting / coding artifact 3Lab value / disease marker 4Not in label — unassessed 26
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.
- 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. 98 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
Show:
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Bacteraemia | 22 | 14.3 9.4–21.6ROR 14.4 · χ² 258 / p 2e-58 | 13.7 EB05 9.1 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious PRR 11.8 | no trial data cached |
| Pneumocystis jirovecii pneumonia | 15 | 11.4 6.9–19.0ROR 11.5 · χ² 133 / p 5e-31 | 10.1 EB05 6.0 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 9.4 | no trial data cached |
| Herpes zoster (shingles) | 75 | 9.9 8.0–12.4ROR 10.2 · χ² 595 / p 1e-131 | 9.7 EB05 7.9 · IC025 +2.8 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 9.2 | no trial data cached |
| Acute myeloid leukaemia | 20 | 9.8 6.3–15.2ROR 9.9 · χ² 149 / p 1e-34 | 8.7 EB05 5.7 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 8.1 | no trial data cached |
| Renal tubular necrosis | 11 | 8.5 4.7–15.4ROR 8.6 · χ² 66 / p 3e-16 | 6.8 EB05 3.9 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 7.1 | no trial data cached |
| Osteopenia | 17 | 8.5 5.3–13.7ROR 8.5 · χ² 105 / p 6e-25 | 7.3 EB05 4.7 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 7.3 | no trial data cached |
| Economic problem | 17 | 8.4 5.2–13.5ROR 8.5 · χ² 104 / p 1e-24 | 7.2 EB05 4.6 · IC025 +2.0 3/3 methods agree | Reporting / coding artifact | serious PRR 7.1 | no trial data cached |
| Cytopenia | 13 | 8.3 4.8–14.3ROR 8.3 · χ² 76 / p 1e-18 | 6.8 EB05 4.1 · IC025 +1.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.1 | no trial data cached |
| Erythema multiforme | 10 | 8.2 4.4–15.2ROR 8.2 · χ² 56 / p 4e-14 | 6.4 EB05 3.6 · IC025 +1.5 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.0 | no trial data cached |
| Febrile neutropenia | 70 | 8.1 6.4–10.2ROR 8.2 · χ² 427 / p 4e-95 | 7.8 EB05 6.3 · IC025 +2.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 6.7 · ♀ 28% (drug 60%) · 96% clinician | no trial data cached |
| No therapeutic response | 12 | 7.4 4.2–13.0ROR 7.4 · χ² 60 / p 5e-15 | 6.0 EB05 3.6 · IC025 +1.6 3/3 methods agree | Reporting / coding artifact | serious PRR 8.5 | no trial data cached |
| Anhedonia | 25 | 7.2 4.9–10.6ROR 7.3 · χ² 127 / p 8e-30 | 6.5 EB05 4.6 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · ♀ 28% (drug 60%) | no trial data cached |
| Drug resistance | 24 | 7.1 4.8–10.6ROR 7.2 · χ² 120 / p 3e-28 | 6.4 EB05 4.5 · IC025 +2.0 3/3 methods agree | Reporting / coding artifact | serious PRR 6.6 · 95% clinician | no trial data cached |
| Sinus tachycardia | 13 | 7.0 4.1–12.0ROR 7.0 · χ² 61 / p 3e-15 | 5.8 EB05 3.6 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 5.9 | no trial data cached |
| Eye pain | 50 | 6.9 5.2–9.1ROR 7.0 · χ² 247 / p 6e-56 | 6.5 EB05 5.1 · IC025 +2.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.2 · 72% consumer | no trial data cached |
| Acute respiratory failure | 16 | 6.4 3.9–10.4ROR 6.4 · χ² 67 / p 1e-16 | 5.5 EB05 3.6 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 | no trial data cached |
| Ankle fracture | 12 | 5.9 3.4–10.4ROR 5.9 · χ² 44 / p 2e-11 | 4.9 EB05 3.0 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| Respiratory distress | 20 | 5.5 3.6–8.5ROR 5.6 · χ² 70 / p 4e-17 | 4.9 EB05 3.4 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Oral herpes | 14 | 5.5 3.3–9.3ROR 5.5 · χ² 47 / p 4e-12 | 4.7 EB05 3.0 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 1.5 | no trial data cached |
| Plasma cell myeloma | 28 | 5.5 3.8–7.9ROR 5.5 · χ² 98 / p 2e-23 | 5.0 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 | no trial data cached |
| Photophobia (light sensitivity) | 13 | 5.3 3.1–9.1ROR 5.3 · χ² 41 / p 7e-11 | 4.5 EB05 2.8 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 1.1 | no trial data cached |
| Blood lactate dehydrogenase increased | 11 | 5.3 2.9–9.5ROR 5.3 · χ² 34 / p 3e-9 | 4.4 EB05 2.6 · IC025 +1.1 3/3 methods agree | Lab value / disease marker | serious PRR 4.6 | no trial data cached |
| Blood pressure systolic increased | 13 | 5.1 2.9–8.7ROR 5.1 · χ² 38 / p 3e-10 | 4.3 EB05 2.7 · IC025 +1.2 3/3 methods agree | Lab value / disease marker | serious PRR 4.5 | no trial data cached |
| End stage renal disease | 12 | 5.0 2.8–8.7ROR 5.0 · χ² 34 / p 3e-9 | 4.2 EB05 2.6 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 4.1 | no trial data cached |
| Haematocrit decreased | 13 | 5.0 2.9–8.5ROR 5.0 · χ² 37 / p 5e-10 | 4.3 EB05 2.7 · IC025 +1.2 3/3 methods agree | Lab value / disease marker | serious PRR 4.3 | no trial data cached |
| Lymphocyte count decreased | 11 | 4.7 2.6–8.6ROR 4.8 · χ² 29 / p 4e-8 | 4.0 EB05 2.4 · IC025 +1.0 3/3 methods agree | Lab value / disease marker | serious PRR 4.3 | no trial data cached |
| Neuropathy peripheral (nerve damage in hands/feet) | 57 | 4.6 3.6–5.9ROR 4.7 · χ² 157 / p 2e-36 | 4.4 EB05 3.6 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Cytomegalovirus infection | 10 | 4.6 2.5–8.5ROR 4.6 · χ² 25 / p 4e-7 | 3.9 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Upper gastrointestinal haemorrhage | 10 | 4.5 2.4–8.4ROR 4.5 · χ² 24 / p 5e-7 | 3.8 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.7 | no trial data cached |
| Pancytopenia (all blood cells low) | 33 | 4.5 3.2–6.3ROR 4.6 · χ² 87 / p 6e-21 | 4.3 EB05 3.2 · IC025 +1.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.6 | no trial data cached |
| Tubulointerstitial nephritis | 11 | 4.5 2.5–8.1ROR 4.5 · χ² 26 / p 1e-7 | 3.8 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.7 | no trial data cached |
| Rash maculo-papular | 13 | 4.5 2.6–7.7ROR 4.5 · χ² 32 / p 9e-9 | 3.9 EB05 2.5 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 4.1 | no trial data cached |
| Rib fracture | 12 | 4.5 2.5–7.8ROR 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 4.0 | no trial data cached |
| Hypocalcaemia (low calcium) | 11 | 4.4 2.5–8.0ROR 4.5 · χ² 26 / p 2e-7 | 3.8 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 3.9 | no trial data cached |
| Urinary incontinence | 17 | 4.4 2.7–7.0ROR 4.4 · χ² 41 / p 8e-11 | 4.0 EB05 2.6 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.8 | no trial data cached |
| Rash generalised | 15 | 4.4 2.6–7.2ROR 4.4 · χ² 35 / p 1e-9 | 3.9 EB05 2.5 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 5.3 | no trial data cached |
| Neutrophil count decreased | 23 | 4.3 2.9–6.5ROR 4.4 · χ² 56 / p 4e-14 | 4.0 EB05 2.8 · IC025 +1.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.8 | no trial data cached |
| Pericardial effusion | 13 | 4.3 2.5–7.4ROR 4.3 · χ² 30 / p 2e-8 | 3.8 EB05 2.4 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
| Eating disorder | 12 | 4.3 2.4–7.5ROR 4.3 · χ² 27 / p 1e-7 | 3.7 EB05 2.3 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 2.9 | no trial data cached |
| Eye irritation | 31 | 4.2 3.0–6.0ROR 4.3 · χ² 74 / p 5e-18 | 4.0 EB05 3.0 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 2.2 | 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 |
|---|---|---|---|---|---|---|
| Herpes zoster (shingles) | 75 | 9.9 8.0–12.4ROR 10.2 · χ² 595 / p 1e-131 | 9.7 EB05 7.9 · IC025 +2.8 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 9.2 | no trial data cached |
| Febrile neutropenia | 70 | 8.1 6.4–10.2ROR 8.2 · χ² 427 / p 4e-95 | 7.8 EB05 6.3 · IC025 +2.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 6.7 · ♀ 28% (drug 60%) · 96% clinician | no trial data cached |
| Platelet count decreased | 57 | 4.1 3.2–5.3ROR 4.1 · χ² 130 / p 2e-30 | 4.0 EB05 3.2 · IC025 +1.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.4 | no trial data cached |
| Neuropathy peripheral (nerve damage in hands/feet) | 57 | 4.6 3.6–5.9ROR 4.7 · χ² 157 / p 2e-36 | 4.4 EB05 3.6 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Neutropenia (low neutrophils (infection-fighting cells)) | 51 | 2.9 2.2–3.8ROR 2.9 · χ² 61 / p 3e-15 | 2.8 EB05 2.2 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.3 | no trial data cached |
| Eye pain | 50 | 6.9 5.2–9.1ROR 7.0 · χ² 247 / p 6e-56 | 6.5 EB05 5.1 · IC025 +2.2 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.2 · 72% consumer | no trial data cached |
| White blood cell count decreased | 49 | 3.4 2.6–4.5ROR 3.5 · χ² 83 / p 4e-20 | 3.3 EB05 2.6 · IC025 +1.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 2.6 | no trial data cached |
| Chronic kidney disease | 36 | 3.6 2.6–5.0ROR 3.6 · χ² 65 / p 5e-16 | 3.4 EB05 2.6 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 3.0 | no trial data cached |
| Emotional distress | 34 | 2.1 1.5–3.0ROR 2.1 · χ² 19 / p 5e-6 | 2.1 EB05 1.6 · IC025 +0.5 | Not in label — unassessed | serious PRR 1.9 · ♀ 38% (drug 60%) | no trial data cached |
| Pancytopenia (all blood cells low) | 33 | 4.5 3.2–6.3ROR 4.6 · χ² 87 / p 6e-21 | 4.3 EB05 3.2 · IC025 +1.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.6 | no trial data cached |
| Epistaxis (nosebleed) | 32 | 3.3 2.3–4.6ROR 3.3 · χ² 48 / p 2e-12 | 3.1 EB05 2.3 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
| Stomatitis (mouth sores) | 32 | 4.0 2.8–5.7ROR 4.1 · χ² 70 / p 3e-17 | 3.8 EB05 2.8 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 · ♀ 29% (drug 60%) | no trial data cached |
| Eye irritation | 31 | 4.2 3.0–6.0ROR 4.3 · χ² 74 / p 5e-18 | 4.0 EB05 3.0 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 2.2 | no trial data cached |
| Plasma cell myeloma | 28 | 5.5 3.8–7.9ROR 5.5 · χ² 98 / p 2e-23 | 5.0 EB05 3.7 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 4.2 | no trial data cached |
| Rash pruritic | 27 | 3.8 2.6–5.6ROR 3.8 · χ² 53 / p 1e-13 | 3.6 EB05 2.6 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 · ♀ 81% (drug 60%) | 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.
- Bacteraemia — n=22, PRR 14.3
- Acute myeloid leukaemia — n=20, PRR 9.8
- Anhedonia — n=25, PRR 7.2
- Respiratory distress — n=20, PRR 5.5
- Plasma cell myeloma — n=28, PRR 5.5
- Neuropathy peripheral — n=57, PRR 4.6
- Eye irritation — n=31, PRR 4.2
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 Famciclovir?
In FDA FAERS, the most frequently co-reported reaction terms for Famciclovir are herpes zoster, febrile neutropenia, platelet count decreased, neuropathy peripheral, neutropenia, eye pain. 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 Famciclovir have an FDA boxed warning?
No. The FDA label retrieved for Famciclovir has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Famciclovir 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 08c58224-5920-4853-8c59-ec5fbb66c2f6, effective 20250109; matched on
openfda.generic_name.exact:"FAMCICLOVIR") - 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, fieldpatient.drug.openfda.generic_name.exact, 138 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.