Nafcillin Sodium side effects: what 918 FDA adverse event reports show

Nafcillin Sodium · 26 reaction terms · 430 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Who reports

918 reports · 85% serious · 110 with death outcome · 34% female

openFDA FAERS counts, all years, deduplication not applied

Used for

Nafcillin is indicated in the treatment of infections caused by penicillinase-producing staphylococci which have demonstrated susceptibility to the drug. Culture and susceptibility tests should be performed initially to determine the causative organism and its susceptibility to the drug (see CLINICAL PHARMACOLOGY - Susceptibility Test Methods ).

FDA label, Indications and Usage

What it is

DESCRIPTION Nafcillin for Injection, USP is a semisynthetic antibiotic penicillin derived from the penicillin nucleus 6-aminopenicillanic acid. It is the sodium salt in a parenteral dosage form.

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 18 strongest signals

Labeled adverse reaction 1Labeled (related wording) 2Likely indication confounding 1Lab value / disease marker 3Not 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.
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.
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. 8 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
Tubulointerstitial nephritis	43	52.6 39.2–70.4ROR 55.1 · χ² 2,120 / p <1e-300	51.3 EB05 39.7 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious PRR 32.4 · ♀ 12% (drug 34%) · 100% clinician	no trial data cached
Nephropathy toxic	24	49.3 33.2–73.2ROR 50.6 · χ² 1,087 / p 1e-238	47.5 EB05 33.6 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious PRR 34.3 · 100% clinician	no trial data cached
Renal failure acute	64	34.0 26.8–43.1ROR 36.5 · χ² 2,019 / p <1e-300	33.7 EB05 27.3 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious PRR 20.4 · 95% clinician	no trial data cached
Renal tubular necrosis	11	25.6 14.2–46.0ROR 25.9 · χ² 236 / p 2e-53	24.4 EB05 14.3 · IC025 +2.6 3/3 methods agree	Labeled (related wording) related wording	serious PRR 14.3	no trial data cached
Hypokalaemia (low potassium)	42	20.9 15.6–28.1ROR 21.9 · χ² 778 / p 2e-171	20.7 EB05 16.0 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious PRR 13.8 · 100% clinician	no trial data cached
Eosinophilia	13	17.0 9.9–29.2ROR 17.2 · χ² 180 / p 2e-41	16.1 EB05 9.3 · IC025 +2.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 11.2	no trial data cached
Hepatotoxicity (liver damage)	15	15.5 9.4–25.6ROR 15.7 · χ² 189 / p 3e-43	14.6 EB05 8.7 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 10.7	no trial data cached
Blood urea increased	11	14.9 8.3–26.9ROR 15.1 · χ² 129 / p 3e-30	13.5 EB05 7.0 · IC025 +2.2 3/3 methods agree	Lab value / disease marker	serious PRR 11.2	no trial data cached
Anhedonia	16	13.8 8.5–22.4ROR 14.0 · χ² 178 / p 8e-41	12.9 EB05 7.8 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 10.4	no trial data cached
Renal injury	18	13.7 8.7–21.7ROR 14.0 · χ² 200 / p 1e-45	12.9 EB05 8.1 · IC025 +2.6 3/3 methods agree	Not in label — unassessed	serious PRR 9.3	no trial data cached
Blood bilirubin increased	16	13.5 8.3–21.9ROR 13.7 · χ² 173 / p 8e-40	12.5 EB05 7.5 · IC025 +2.4 3/3 methods agree	Lab value / disease marker	serious PRR 8.6	no trial data cached
Fear	16	13.5 8.3–21.9ROR 13.7 · χ² 173 / p 9e-40	12.5 EB05 7.5 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 12.5	no trial data cached
Rash generalised	15	13.1 7.9–21.6ROR 13.3 · χ² 155 / p 6e-36	11.9 EB05 7.0 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 11.1	no trial data cached
Staphylococcal infection	18	12.4 7.9–19.6ROR 12.7 · χ² 178 / p 6e-41	11.5 EB05 7.2 · IC025 +2.5 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious PRR 8.8	no trial data cached
Serotonin syndrome	10	11.9 6.4–22.1ROR 12.1 · χ² 90 / p 1e-21	9.9 EB05 5.0 · IC025 +1.9 3/3 methods agree	Not in label — unassessed	serious PRR 8.2	no trial data cached
Drug-induced liver injury	16	11.9 7.3–19.3ROR 12.0 · χ² 148 / p 2e-34	10.7 EB05 6.4 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 8.1	no trial data cached
Drug reaction with eosinophilia and systemic symptoms	13	11.6 6.8–19.9ROR 11.8 · χ² 116 / p 2e-27	10.1 EB05 5.7 · IC025 +2.1 3/3 methods agree	Labeled (related wording) related wording	serious PRR 7.3	no trial data cached
International normalised ratio increased	12	9.5 5.4–16.7ROR 9.6 · χ² 83 / p 4e-20	7.8 EB05 4.5 · IC025 +1.8 3/3 methods agree	Lab value / disease marker	serious PRR 5.4	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
Renal failure acute	64	34.0 26.8–43.1ROR 36.5 · χ² 2,019 / p <1e-300	33.7 EB05 27.3 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious PRR 20.4 · 95% clinician	no trial data cached
Tubulointerstitial nephritis	43	52.6 39.2–70.4ROR 55.1 · χ² 2,120 / p <1e-300	51.3 EB05 39.7 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious PRR 32.4 · ♀ 12% (drug 34%) · 100% clinician	no trial data cached
Hypokalaemia (low potassium)	42	20.9 15.6–28.1ROR 21.9 · χ² 778 / p 2e-171	20.7 EB05 16.0 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious PRR 13.8 · 100% clinician	no trial data cached
Nephropathy toxic	24	49.3 33.2–73.2ROR 50.6 · χ² 1,087 / p 1e-238	47.5 EB05 33.6 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious PRR 34.3 · 100% clinician	no trial data cached
Staphylococcal infection	18	12.4 7.9–19.6ROR 12.7 · χ² 178 / p 6e-41	11.5 EB05 7.2 · IC025 +2.5 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious PRR 8.8	no trial data cached
Renal injury	18	13.7 8.7–21.7ROR 14.0 · χ² 200 / p 1e-45	12.9 EB05 8.1 · IC025 +2.6 3/3 methods agree	Not in label — unassessed	serious PRR 9.3	no trial data cached
Drug-induced liver injury	16	11.9 7.3–19.3ROR 12.0 · χ² 148 / p 2e-34	10.7 EB05 6.4 · IC025 +2.3 3/3 methods agree	Not in label — unassessed	serious PRR 8.1	no trial data cached
Fear	16	13.5 8.3–21.9ROR 13.7 · χ² 173 / p 9e-40	12.5 EB05 7.5 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 12.5	no trial data cached
Blood bilirubin increased	16	13.5 8.3–21.9ROR 13.7 · χ² 173 / p 8e-40	12.5 EB05 7.5 · IC025 +2.4 3/3 methods agree	Lab value / disease marker	serious PRR 8.6	no trial data cached
Anhedonia	16	13.8 8.5–22.4ROR 14.0 · χ² 178 / p 8e-41	12.9 EB05 7.8 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 10.4	no trial data cached
Rash generalised	15	13.1 7.9–21.6ROR 13.3 · χ² 155 / p 6e-36	11.9 EB05 7.0 · IC025 +2.4 3/3 methods agree	Not in label — unassessed	serious PRR 11.1	no trial data cached
Hepatotoxicity (liver damage)	15	15.5 9.4–25.6ROR 15.7 · χ² 189 / p 3e-43	14.6 EB05 8.7 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious PRR 10.7	no trial data cached
Drug reaction with eosinophilia and systemic symptoms	13	11.6 6.8–19.9ROR 11.8 · χ² 116 / p 2e-27	10.1 EB05 5.7 · IC025 +2.1 3/3 methods agree	Labeled (related wording) related wording	serious PRR 7.3	no trial data cached
Eosinophilia	13	17.0 9.9–29.2ROR 17.2 · χ² 180 / p 2e-41	16.1 EB05 9.3 · IC025 +2.5 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 11.2	no trial data cached
International normalised ratio increased	12	9.5 5.4–16.7ROR 9.6 · χ² 83 / p 4e-20	7.8 EB05 4.5 · IC025 +1.8 3/3 methods agree	Lab value / disease marker	serious PRR 5.4	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.

Tubulointerstitial nephritis — n=43, PRR 52.6
Nephropathy toxic — n=24, PRR 49.3
Renal failure acute — n=64, PRR 34.0
Hypokalaemia — n=42, PRR 20.9

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 Nafcillin?

In FDA FAERS, the most frequently co-reported reaction terms for Nafcillin are renal failure acute, tubulointerstitial nephritis, hypokalaemia, nephropathy toxic, staphylococcal infection, renal injury. 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 Nafcillin have an FDA boxed warning?

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

Do FAERS signals prove that Nafcillin 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 91ebf84a-310f-4271-8446-5a10a877883a, effective 20240227; matched on openfda.generic_name.exact:"NAFCILLIN")
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, 26 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.