Drug · FAERS side-effect profile with label screen
Amifampridine side effects: what 2,868 FDA adverse event reports show
Drug class
Potassium channel blocker
FDA label, Indications wording of the closest related product
Label matched
Amifampridine Phosphate (Firdapse)
closest FDA label found for this product string; brand list suppressed because the label is a related product, not an exact match
Who reports
2,868 reports · 52% serious · 207 with death outcome · 61% female
openFDA FAERS counts, all years, deduplication not applied
Used for
FIRDAPSE ® is indicated for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in adults and pediatric patients 6 years of age and older. FIRDAPSE is a potassium channel blocker indicated for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in adults and pediatric patients 6 years of age and older. ( 1 )
FDA label, Indications and Usage
What it is
The active ingredient of FIRDAPSE is amifampridine phosphate, which is a voltage-gated potassium channel blocker. Amifampridine phosphate is described chemically as 3,4-diaminopyridine phosphate with a molecular weight of 207.1 and a molecular formula of C 5 H 7 N 3 • H 3 PO 4 .
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 3Labeled (related wording) 1Reporting / coding artifact 7Not in label — unassessed 29
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.
- 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. 128 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 |
|---|---|---|---|---|---|---|
| Paraesthesia oral | 264 | 136.8 121.8–153.7ROR 150.6 · χ² 34,822 / p <1e-300 | 133.0 EB05 120.1 · IC025 +6.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 102.3 · 96% consumer | no trial data cached |
| Hypoaesthesia oral | 105 | 51.3 42.5–62.0ROR 53.2 · χ² 5,099 / p <1e-300 | 50.5 EB05 42.9 · IC025 +5.0 3/3 methods agree | Not in label — unassessed | serious PRR 43.2 · 97% consumer | no trial data cached |
| Therapeutic response shortened | 92 | 21.2 17.3–25.9ROR 21.9 · χ² 1,748 / p <1e-300 | 21.1 EB05 17.7 · IC025 +3.9 3/3 methods agree | Reporting / coding artifact | serious PRR 26.1 · 95% consumer | no trial data cached |
| Peripheral coldness | 36 | 19.1 13.8–26.5ROR 19.4 · χ² 600 / p 9e-133 | 18.9 EB05 14.2 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious PRR 19.6 · ♀ 89% (drug 61%) · 94% consumer | no trial data cached |
| Diplopia (double vision) | 59 | 16.6 12.9–21.4ROR 17.0 · χ² 851 / p 2e-187 | 16.5 EB05 13.2 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious PRR 15.7 · 97% consumer | no trial data cached |
| Paraesthesia (tingling/numbness) | 327 | 15.2 13.7–16.8ROR 17.0 · χ² 4,344 / p <1e-300 | 15.1 EB05 13.8 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.1 · 97% consumer | no trial data cached |
| Eyelid ptosis | 19 | 13.7 8.7–21.4ROR 13.8 · χ² 211 / p 5e-48 | 12.9 EB05 8.2 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious n=12 | no trial data cached |
| Feeling cold | 51 | 13.4 10.2–17.6ROR 13.6 · χ² 572 / p 1e-126 | 13.2 EB05 10.3 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious PRR 14.6 · 96% consumer | no trial data cached |
| Muscular weakness | 194 | 12.5 10.9–14.3ROR 13.3 · χ² 2,049 / p <1e-300 | 12.4 EB05 11.0 · IC025 +3.4 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 12.5 · 94% consumer | no trial data cached |
| Prescribed overdose | 33 | 12.5 8.9–17.5ROR 12.6 · χ² 337 / p 1e-75 | 12.0 EB05 8.7 · IC025 +2.8 3/3 methods agree | Not in label — unassessed | serious PRR 13.5 · 94% consumer | no trial data cached |
| Brain fog | 24 | 12.0 8.1–17.9ROR 12.1 · χ² 232 / p 1e-52 | 11.3 EB05 7.7 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 14.9 · 100% consumer | no trial data cached |
| Malnutrition | 15 | 9.9 6.0–16.4ROR 9.9 · χ² 111 / p 3e-26 | 8.5 EB05 5.1 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 11.3 | no trial data cached |
| Pulmonary mass | 20 | 9.8 6.4–15.2ROR 9.9 · χ² 150 / p 8e-35 | 8.8 EB05 5.7 · IC025 +2.3 3/3 methods agree | Not in label — unassessed | serious PRR 11.2 · 95% consumer | no trial data cached |
| Limb discomfort | 41 | 9.7 7.2–13.1ROR 9.8 · χ² 311 / p 6e-70 | 9.2 EB05 6.9 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 11.5 · 100% consumer | no trial data cached |
| Therapeutic product effect incomplete | 87 | 9.0 7.3–11.1ROR 9.3 · χ² 612 / p 2e-135 | 8.8 EB05 7.3 · IC025 +2.7 3/3 methods agree | Reporting / coding artifact | serious PRR 9.5 · 89% consumer | no trial data cached |
| Aspiration | 13 | 8.8 5.1–15.1ROR 8.8 · χ² 82 / p 7e-20 | 7.2 EB05 4.3 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 10.0 | no trial data cached |
| Autoimmune disorder | 11 | 8.4 4.7–15.2ROR 8.4 · χ² 65 / p 5e-16 | 6.7 EB05 3.8 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 9.9 | no trial data cached |
| Incontinence | 12 | 8.3 4.7–14.6ROR 8.3 · χ² 70 / p 3e-17 | 6.7 EB05 4.0 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 7.2 | no trial data cached |
| Skin laceration | 12 | 8.1 4.6–14.3ROR 8.2 · χ² 68 / p 8e-17 | 6.6 EB05 3.9 · IC025 +1.7 3/3 methods agree | Not in label — unassessed | serious PRR 10.8 | no trial data cached |
| Leukocytosis | 20 | 8.1 5.2–12.5ROR 8.1 · χ² 117 / p 1e-27 | 7.1 EB05 4.7 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 9.1 · ♀ 90% (drug 61%) · 80% consumer | no trial data cached |
| Acute respiratory failure | 21 | 8.0 5.2–12.3ROR 8.1 · χ² 122 / p 1e-28 | 7.1 EB05 4.8 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 8.9 | no trial data cached |
| Motor dysfunction | 11 | 8.0 4.4–14.4ROR 8.0 · χ² 60 / p 5e-15 | 6.3 EB05 3.7 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 9.0 | no trial data cached |
| Gait inability | 34 | 7.5 5.4–10.5ROR 7.6 · χ² 186 / p 1e-42 | 6.9 EB05 5.1 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 9.4 · 91% consumer | no trial data cached |
| Rib fracture | 21 | 7.5 4.9–11.5ROR 7.5 · χ² 112 / p 2e-26 | 6.6 EB05 4.5 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 9.0 · 95% consumer | no trial data cached |
| Movement disorder | 33 | 7.5 5.3–10.5ROR 7.6 · χ² 179 / p 4e-41 | 6.9 EB05 5.1 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 6.1 · 94% consumer | no trial data cached |
| Diverticulitis | 28 | 7.4 5.1–10.7ROR 7.5 · χ² 149 / p 1e-34 | 6.7 EB05 4.8 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 8.7 · ♀ 82% (drug 61%) · 93% consumer | no trial data cached |
| Product substitution issue | 58 | 7.4 5.7–9.5ROR 7.5 · χ² 314 / p 2e-70 | 7.0 EB05 5.6 · IC025 +2.4 3/3 methods agree | Reporting / coding artifact | serious PRR 9.0 · 97% consumer | no trial data cached |
| Gastroenteritis viral | 18 | 7.3 4.6–11.5ROR 7.3 · χ² 91 / p 6e-22 | 6.3 EB05 4.2 · IC025 +1.8 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Unevaluable event | 75 | 7.3 5.8–9.1ROR 7.4 · χ² 399 / p 4e-89 | 7.0 EB05 5.7 · IC025 +2.4 3/3 methods agree | Reporting / coding artifact | serious PRR 8.5 · 97% consumer | no trial data cached |
| Balance disorder | 85 | 7.2 5.8–8.9ROR 7.4 · χ² 448 / p 1e-99 | 7.0 EB05 5.8 · IC025 +2.4 3/3 methods agree | Not in label — unassessed | serious PRR 8.6 · 99% consumer | no trial data cached |
| Hypoaesthesia (numbness) | 143 | 7.0 6.0–8.2ROR 7.3 · χ² 732 / p 2e-161 | 6.8 EB05 5.9 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · 99% consumer | no trial data cached |
| Muscle twitching | 22 | 7.0 4.6–10.6ROR 7.0 · χ² 107 / p 3e-25 | 6.2 EB05 4.3 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 6.5 · 91% consumer | no trial data cached |
| Asthenia (weakness) | 356 | 6.9 6.3–7.6ROR 7.8 · χ² 1,831 / p <1e-300 | 6.9 EB05 6.3 · IC025 +2.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.2 · 90% consumer | no trial data cached |
| Therapeutic product effect decreased | 39 | 6.4 4.7–8.8ROR 6.5 · χ² 174 / p 6e-40 | 6.0 EB05 4.6 · IC025 +2.1 3/3 methods agree | Reporting / coding artifact | serious PRR 6.1 · 92% consumer | no trial data cached |
| Dysphagia (difficulty swallowing) | 80 | 6.2 5.0–7.7ROR 6.3 · χ² 344 / p 5e-77 | 6.0 EB05 5.0 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 6.6 · 96% consumer | no trial data cached |
| Intentional product use issue | 73 | 6.1 4.8–7.6ROR 6.2 · χ² 305 / p 1e-68 | 5.9 EB05 4.8 · IC025 +2.2 3/3 methods agree | Reporting / coding artifact | serious PRR 6.6 · 94% consumer | no trial data cached |
| Muscle atrophy | 10 | 5.8 3.1–10.8ROR 5.8 · χ² 35 / p 1e-9 | 4.7 EB05 2.7 · IC025 +1.2 3/3 methods agree | Not in label — unassessed | serious PRR 7.5 | no trial data cached |
| Cold sweat | 14 | 5.8 3.4–9.8ROR 5.8 · χ² 51 / p 5e-13 | 4.9 EB05 3.1 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| Dry mouth | 63 | 5.7 4.5–7.3ROR 5.8 · χ² 240 / p 2e-54 | 5.5 EB05 4.4 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 · 97% consumer | no trial data cached |
| Treatment noncompliance | 42 | 5.7 4.2–7.6ROR 5.7 · χ² 157 / p 3e-36 | 5.3 EB05 4.1 · IC025 +1.9 3/3 methods agree | Reporting / coding artifact | serious PRR 5.3 · 98% consumer | 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 |
|---|---|---|---|---|---|---|
| Asthenia (weakness) | 356 | 6.9 6.3–7.6ROR 7.8 · χ² 1,831 / p <1e-300 | 6.9 EB05 6.3 · IC025 +2.6 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.2 · 90% consumer | no trial data cached |
| Paraesthesia (tingling/numbness) | 327 | 15.2 13.7–16.8ROR 17.0 · χ² 4,344 / p <1e-300 | 15.1 EB05 13.8 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 13.1 · 97% consumer | no trial data cached |
| Paraesthesia oral | 264 | 136.8 121.8–153.7ROR 150.6 · χ² 34,822 / p <1e-300 | 133.0 EB05 120.1 · IC025 +6.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 102.3 · 96% consumer | no trial data cached |
| Fall | 238 | 5.2 4.6–5.9ROR 5.6 · χ² 824 / p 2e-181 | 5.2 EB05 4.7 · IC025 +2.2 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 5.9 · 92% consumer | no trial data cached |
| Condition aggravated | 200 | 4.8 4.2–5.5ROR 5.1 · χ² 615 / p 5e-136 | 4.8 EB05 4.3 · IC025 +2.0 3/3 methods agree | Reporting / coding artifact | serious PRR 6.6 · 94% consumer | no trial data cached |
| Muscular weakness | 194 | 12.5 10.9–14.3ROR 13.3 · χ² 2,049 / p <1e-300 | 12.4 EB05 11.0 · IC025 +3.4 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 12.5 · 94% consumer | no trial data cached |
| Product dose omission issue | 147 | 3.8 3.2–4.4ROR 3.9 · χ² 301 / p 9e-68 | 3.7 EB05 3.3 · IC025 +1.6 3/3 methods agree | Reporting / coding artifact | serious PRR 11.7 · 96% consumer | no trial data cached |
| Hypoaesthesia (numbness) | 143 | 7.0 6.0–8.2ROR 7.3 · χ² 732 / p 2e-161 | 6.8 EB05 5.9 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · 99% consumer | no trial data cached |
| Abdominal pain upper | 137 | 4.9 4.1–5.7ROR 5.1 · χ² 422 / p 4e-94 | 4.8 EB05 4.2 · IC025 +2.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 5.6 · 96% consumer | no trial data cached |
| Gait disturbance | 135 | 5.1 4.4–6.1ROR 5.4 · χ² 451 / p 3e-100 | 5.1 EB05 4.4 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 6.1 · 96% consumer | no trial data cached |
| Muscle spasms | 110 | 4.4 3.6–5.3ROR 4.5 · χ² 286 / p 2e-64 | 4.3 EB05 3.7 · IC025 +1.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 5.5 · 99% consumer | no trial data cached |
| Abdominal discomfort | 110 | 4.8 4.0–5.8ROR 5.0 · χ² 331 / p 3e-74 | 4.7 EB05 4.0 · IC025 +1.9 3/3 methods agree | Not in label — unassessed | serious PRR 6.0 · 95% consumer | no trial data cached |
| Feeling abnormal | 105 | 3.2 2.6–3.9ROR 3.3 · χ² 158 / p 2e-36 | 3.2 EB05 2.7 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 4.5 · 95% consumer | no trial data cached |
| Hypoaesthesia oral | 105 | 51.3 42.5–62.0ROR 53.2 · χ² 5,099 / p <1e-300 | 50.5 EB05 42.9 · IC025 +5.0 3/3 methods agree | Not in label — unassessed | serious PRR 43.2 · 97% consumer | no trial data cached |
| Urinary tract infection (bladder infection) | 102 | 4.4 3.6–5.3ROR 4.5 · χ² 265 / p 6e-60 | 4.3 EB05 3.6 · IC025 +1.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.2 · 92% 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.
- Hypoaesthesia oral — n=105, PRR 51.3
- Peripheral coldness — n=36, PRR 19.1
- Diplopia — n=59, PRR 16.6
- Feeling cold — n=51, PRR 13.4
- Prescribed overdose — n=33, PRR 12.5
- Brain fog — n=24, PRR 12.0
- Pulmonary mass — n=20, PRR 9.8
- Limb discomfort — n=41, PRR 9.7
- Leukocytosis — n=20, PRR 8.1
- Acute respiratory failure — n=21, PRR 8.0
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 Amifampridine?
In FDA FAERS, the most frequently co-reported reaction terms for Amifampridine are asthenia, paraesthesia, paraesthesia oral, fall, muscular weakness, hypoaesthesia. 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 Amifampridine have an FDA boxed warning?
No. The FDA label retrieved for Amifampridine has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Amifampridine 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 f015fe60-3128-4a43-8c31-19fc6b5def3f, effective 20260416; matched on
openfda.generic_name.exact:"AMIFAMPRIDINE PHOSPHATE") - 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, 168 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.