Drug · FAERS side-effect profile with label screen
Acyclovir side effects: what 113,469 FDA adverse event reports show
Drug class
Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitor, Herpes Zoster Virus Nucleoside Analog DNA Polymerase Inhibitor, Herpesvirus Nucleoside Analog DNA Polymerase Inhibitor
FDA label (Established Pharmacologic Class) · compare the class
Who reports
113,469 reports · 73% serious · 14,477 with death outcome · 50% female
openFDA FAERS counts, all years, deduplication not applied
Used for
Herpes Zoster Infections: Acyclovir capsules are indicated for the acute treatment of herpes zoster (shingles). Genital Herpes: Acyclovir capsules are indicated for the treatment of initial episodes and the management of recurrent episodes of genital herpes. Chickenpox: Acyclovir capsules are indicated for the treatment of chickenpox (varicella).
FDA label, Indications and Usage
What it is
DESCRIPTION Acyclovir is a synthetic nucleoside analogue active against herpesviruses. Acyclovir capsules are formulation for oral administration. Acyclovir is a white or almost white, crystalline powder with the molecular formula C 8 H 11 N 5 O 3 and a molecular weight of 225.20.
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 1Likely indication confounding 1Lab value / disease marker 10Not in label — unassessed 28
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.
- 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, for the 300 most-reported drugs, adjusted for age band), and flags pairs whose reports are unusually skewed by sex or come mostly from consumers. Each row also shows the PRR against the other drugs of the same FDA class, which removes most confounding by the condition being treated, and a calibrated p-value: on validation, known non-causes average an ROR of about 2, so significance is judged against that empirical null (✓ = p < 0.05 after calibration). 1,194 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 |
|---|---|---|---|---|---|---|
| Sensitisation | 159 | 48.3 40.5–57.5ROR 48.3 · calibrated p 2e-5 ✓ | 38.2 EB05 33.4 · IC025 +4.8 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=158 · ♀ 100% (drug 50%) | not reported in cached trials |
| Ejection fraction | 117 | 46.1 37.6–56.5ROR 46.1 · calibrated p 3e-5 ✓ | 36.7 EB05 31.5 · IC025 +4.7 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=117 · ♀ 100% (drug 50%) | not reported in cached trials |
| Encephalitis herpes | 91 | 41.6 33.2–52.3ROR 41.7 · calibrated p 5e-5 ✓ | 33.8 EB05 28.4 · IC025 +4.5 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=91 · 100% clinician | not reported in cached trials |
| Ophthalmic herpes simplex | 80 | 29.8 23.6–37.8ROR 29.9 · calibrated p 3e-4 ✓ | 25.6 EB05 21.2 · IC025 +4.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=79 · 100% clinician | not reported in cached trials |
| Engraftment syndrome | 76 | 27.3 21.5–34.8ROR 27.3 · calibrated p 5e-4 ✓ | 23.8 EB05 19.6 · IC025 +4.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=76 | not reported in cached trials |
| Light chain analysis increased | 125 | 25.5 21.2–30.8ROR 25.5 · calibrated p 7e-4 ✓ | 22.4 EB05 19.3 · IC025 +4.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=75 | not reported in cached trials |
| Urine leukocyte esterase positive | 79 | 23.1 18.3–29.2ROR 23.1 · calibrated p 0.001 ✓ | 20.5 EB05 17.0 · IC025 +3.8 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=79 · ♀ 100% (drug 50%) · 100% clinician | not reported in cached trials |
| Urinary sediment present | 66 | 21.1 16.3–27.2ROR 21.1 · calibrated p 0.002 ✓ | 18.9 EB05 15.4 · IC025 +3.7 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=66 · ♀ 100% (drug 50%) · 100% clinician | not reported in cached trials |
| Polycystic ovaries | 160 | 20.8 17.7–24.5ROR 20.9 · calibrated p 0.002 ✓ | 18.8 EB05 16.4 · IC025 +3.9 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=160 · ♀ 100% (drug 50%) | not reported in cached trials |
| Red blood cells urine positive | 97 | 20.4 16.6–25.2ROR 20.5 · calibrated p 0.002 ✓ | 18.4 EB05 15.5 · IC025 +3.7 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=95 · ♀ 100% (drug 50%) | not reported in cached trials |
| Plasmacytoma | 154 | 16.4 13.9–19.4ROR 16.4 · calibrated p 0.005 ✓ | 15.1 EB05 13.2 · IC025 +3.6 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=148 · 100% clinician | not reported in cached trials |
| Plasma cell myeloma recurrent | 267 | 16.3 14.4–18.5ROR 16.4 · calibrated p 0.005 ✓ | 15.1 EB05 13.6 · IC025 +3.7 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=197 | not reported in cached trials |
| Monoclonal immunoglobulin present | 62 | 16.2 12.5–21.0ROR 16.2 · calibrated p 0.006 ✓ | 14.8 EB05 11.9 · IC025 +3.3 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | ♀ 0% (drug 50%) · 100% clinician | not reported in cached trials |
| Acute graft versus host disease in intestine | 112 | 15.9 13.1–19.3ROR 16.0 · calibrated p 0.006 ✓ | 14.7 EB05 12.5 · IC025 +3.5 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=112 · 100% clinician | not reported in cached trials |
| Varicella zoster virus infection | 160 | 15.4 13.1–18.1ROR 15.5 · calibrated p 0.006 ✓ | 14.3 EB05 12.5 · IC025 +3.5 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Likely indication confounding shares a disease stem with the indications wording | serious n=159 · 100% clinician | not reported in cached trials |
| Graft versus host disease | 547 | 15.0 13.8–16.4ROR 15.1 · calibrated p 0.007 ✓ | 13.9 EB05 13.0 · IC025 +3.6 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious PRR 11.1 | not reported in cached trials |
| Encephalitis viral | 87 | 14.2 11.4–17.7ROR 14.2 · calibrated p 0.009 ✓ | 13.2 EB05 10.9 · IC025 +3.3 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=87 · 100% clinician | not reported in cached trials |
| Acute graft versus host disease in skin | 197 | 14.1 12.2–16.3ROR 14.2 · calibrated p 0.009 ✓ | 13.1 EB05 11.7 · IC025 +3.4 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=197 · 100% clinician | not reported in cached trials |
| Acute graft versus host disease | 320 | 13.7 12.2–15.3ROR 13.7 · calibrated p 0.010 ✓ | 12.8 EB05 11.6 · IC025 +3.5 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=319 · 100% clinician | not reported in cached trials |
| Neutrophil percentage increased | 87 | 13.5 10.9–16.8ROR 13.6 · calibrated p 0.011 ✓ | 12.5 EB05 10.4 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=86 · 100% clinician | not reported in cached trials |
| Lymphocyte percentage decreased | 90 | 13.2 10.6–16.3ROR 13.2 · calibrated p 0.013 ✓ | 12.2 EB05 10.2 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=89 | not reported in cached trials |
| Cytomegalovirus test positive | 118 | 13.1 10.9–15.8ROR 13.1 · calibrated p 0.013 ✓ | 12.2 EB05 10.4 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=118 · 100% clinician | not reported in cached trials |
| Toxoplasmosis | 72 | 13.1 10.3–16.6ROR 13.1 · calibrated p 0.013 ✓ | 12.1 EB05 9.9 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=71 · ♀ 100% (drug 50%) · 100% clinician | not reported in cached trials |
| Plasma cell myeloma | 2,591 | 13.0 12.5–13.6ROR 13.3 · calibrated p 0.011 ✓ | 12.2 EB05 11.8 · IC025 +3.5 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: PRR 67.1 (50.4–89.2) | Not in label — unassessed | age-adj. PRR 9.9 · serious PRR 8.8 | not reported in cached trials |
| Enterococcal bacteraemia | 69 | 12.9 10.1–16.4ROR 12.9 · calibrated p 0.014 ✓ | 11.9 EB05 9.6 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=68 · ♀ 0% (drug 50%) · 100% clinician | not reported in cached trials |
| Graft versus host disease in skin | 137 | 12.2 10.3–14.5ROR 12.2 · calibrated p 0.016 ✓ | 11.4 EB05 9.8 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=135 | not reported in cached trials |
| Stem cell transplant | 153 | 12.1 10.3–14.3ROR 12.1 · calibrated p 0.017 ✓ | 11.3 EB05 9.9 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=150 | not reported in cached trials |
| Ejection fraction abnormal | 76 | 12.1 9.6–15.3ROR 12.1 · calibrated p 0.018 ✓ | 11.2 EB05 9.2 · IC025 +3.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=76 · ♀ 100% (drug 50%) | not reported in cached trials |
| Systemic mycosis | 72 | 12.1 9.5–15.3ROR 12.1 · calibrated p 0.018 ✓ | 11.2 EB05 9.1 · IC025 +3.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=72 · 100% clinician | not reported in cached trials |
| Cytokine release syndrome | 1,168 | 12.0 11.3–12.7ROR 12.1 · calibrated p 0.016 ✓ | 11.3 EB05 10.8 · IC025 +3.4 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: PRR 103.7 (61.2–175.5) | Not in label — unassessed | age-adj. PRR 12.4 · serious PRR 9.0 · 96% clinician | not reported in cached trials |
| Parainfluenzae virus infection | 93 | 11.7 9.5–14.5ROR 11.8 · calibrated p 0.019 ✓ | 10.9 EB05 9.1 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=92 · ♀ 0% (drug 50%) · 100% clinician | NCT05098938: 1/497 (0.2%) control |
| Pneumonia cytomegaloviral | 115 | 11.7 9.7–14.1ROR 11.7 · calibrated p 0.019 ✓ | 10.9 EB05 9.3 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=114 · 100% clinician | not reported in cached trials |
| White blood cells urine positive | 107 | 11.2 9.2–13.6ROR 11.2 · calibrated p 0.023 ✓ | 10.4 EB05 8.8 · IC025 +3.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=103 · ♀ 100% (drug 50%) | not reported in cached trials |
| Plasma cell myeloma refractory | 74 | 11.1 8.8–14.1ROR 11.1 · calibrated p 0.024 ✓ | 10.3 EB05 8.4 · IC025 +2.9 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=72 | not reported in cached trials |
| Herpes simplex | 368 | 11.1 10.0–12.3ROR 11.1 · calibrated p 0.023 ✓ | 10.4 EB05 9.6 · IC025 +3.2 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled adverse reaction exact term | serious n=330 | not reported in cached trials |
| Chronic graft versus host disease | 206 | 11.0 9.6–12.7ROR 11.0 · calibrated p 0.023 ✓ | 10.4 EB05 9.2 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=205 · 100% clinician | not reported in cached trials |
| Culture urine positive | 80 | 11.0 8.8–13.8ROR 11.0 · calibrated p 0.024 ✓ | 10.2 EB05 8.4 · IC025 +2.9 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Lab value / disease marker | serious n=76 · ♀ 100% (drug 50%) | not reported in cached trials |
| Epstein-barr virus infection reactivation | 70 | 10.8 8.5–13.7ROR 10.8 · calibrated p 0.027 ✓ | 9.9 EB05 8.1 · IC025 +2.9 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=70 · ♀ 0% (drug 50%) · 100% clinician | not reported in cached trials |
| Acute myeloid leukaemia recurrent | 116 | 10.6 8.8–12.8ROR 10.6 · calibrated p 0.028 ✓ | 9.9 EB05 8.4 · IC025 +3.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=116 | not reported in cached trials |
| Immune effector cell-associated neurotoxicity syndrome | 305 | 10.6 9.4–11.8ROR 10.6 · calibrated p 0.027 ✓ | 10.0 EB05 9.1 · IC025 +3.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | serious n=304 · 100% clinician | not reported in cached trials |
Clinical concept groups
MedDRA splits one clinical problem across several terms (e.g. "neutropenia", "neutrophil count decreased", "agranulocytosis"), which dilutes term-level signals. These rows count reports with any term in a concept group (an exact union, not a sum), compared with all other drugs. Groups are hand-built and listed in the methods.
| Concept | Reports | PRR 95% CI | Reading |
|---|---|---|---|
| Neutropenia / agranulocytosis | 7,020 | 5.45.2–5.5 | signal |
| Thrombocytopenia | 5,483 | 4.74.6–4.8 | signal |
| Opportunistic infection | 2,609 | 3.63.5–3.7 | signal |
| Serious infection | 11,432 | 2.82.7–2.8 | signal |
| Anaemia | 4,363 | 2.72.6–2.8 | signal |
| Kidney injury | 6,483 | 2.62.6–2.7 | signal |
| Venous thromboembolism | 3,032 | 2.62.5–2.7 | signal |
| Severe cutaneous reaction | 983 | 2.52.3–2.6 | signal |
| Hyponatraemia | 790 | 1.81.7–2.0 | raised |
| Arrhythmia / qt | 1,781 | 1.71.6–1.8 | raised |
| Liver injury | 2,431 | 1.51.4–1.6 | raised |
| Interstitial lung disease | 686 | 1.31.2–1.4 | raised |
| Heart failure | 1,191 | 1.21.2–1.3 | raised |
| Fall / fracture | 2,525 | 1.21.2–1.3 | raised |
| Osteonecrosis | 368 | 1.21.1–1.3 | raised |
| Seizure | 1,090 | 1.01.0–1.1 | no difference |
Trial evidence (ClinicalTrials.gov)
✓ Trial adverse-event data found on ClinicalTrials.gov
Largest completed trials with posted results that list Acyclovir as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (1 of 40 signal terms matched).
- NCT05098938 — A Study to Compare Sitavig (Acyclovir) Buccal Tablet With a Placebo in the Treatment of Herpes Labialis in Par (N=2020, PHASE3; 196 AE terms posted; arms: Sitavig; Placebo)
Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.
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 |
|---|---|---|---|---|---|---|
| Fatigue (tiredness) | 7,954 | 1.9 1.9–1.9ROR 2.0 · calibrated p 0.926 | 1.9 EB05 1.9 · IC025 +0.9 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | age-adj. PRR 1.6 · serious PRR 1.6 | NCT05098938: 2/504 (0.4%) on Acyclovir; 1/497 (0.2%) control |
| Diarrhoea (diarrhea) | 7,284 | 2.1 2.1–2.2ROR 2.2 · calibrated p 0.962 | 2.1 EB05 2.1 · IC025 +1.0 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled adverse reaction exact term | age-adj. PRR 1.7 · serious PRR 1.7 | NCT05098938: 4/504 (0.8%) on Acyclovir; 3/497 (0.6%) control |
| Off label use (used outside approved label) | 6,225 | 1.3 1.3–1.4ROR 1.3 · calibrated p 0.539 | 1.3 EB05 1.3 · IC025 +0.4 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Reporting / coding artifact | age-adj. PRR 1.5 · serious PRR 1.5 | not reported in cached trials |
| Pneumonia (lung infection) | 5,644 | 3.3 3.2–3.3ROR 3.4 · calibrated p 0.514 | 3.2 EB05 3.2 · IC025 +1.6 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | age-adj. PRR 2.8 · serious PRR 2.6 | NCT05098938: 1/504 (0.2%) on Acyclovir (serious AE) |
| Nausea | 5,561 | 1.3 1.3–1.3ROR 1.3 · calibrated p 0.521 | 1.3 EB05 1.3 · IC025 +0.3 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled adverse reaction exact term | age-adj. PRR 1.1 · serious PRR 1.3 | NCT05098938: 4/504 (0.8%) on Acyclovir; 2/497 (0.4%) control |
| Pyrexia (fever) | 4,899 | 2.6 2.6–2.7ROR 2.7 · calibrated p 0.728 | 2.6 EB05 2.6 · IC025 +1.3 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled (related wording) related wording | age-adj. PRR 2.5 · serious PRR 2.4 | NCT05098938: 2/504 (0.4%) on Acyclovir; 2/497 (0.4%) control |
| Death | 4,869 | 1.0 1.0–1.1ROR 1.0 · calibrated p 0.337 | 1.0 EB05 1.0 · IC025 +0.0 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Outcome field, not a reaction | age-adj. PRR 1.0 · serious PRR 0.8 | NCT05098938: 1/504 (0.2%) on Acyclovir (serious AE) |
| Drug ineffective (drug did not work) | 4,641 | 0.6 0.6–0.7ROR 0.6 · calibrated p 0.099 | 0.7 EB05 0.6 · IC025 -0.7 PRR-only: not supported by EBGM or IC vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Reporting / coding artifact | age-adj. PRR 0.9 · serious PRR 1.1 | not reported in cached trials |
| Rash | 4,245 | 1.8 1.8–1.9ROR 1.8 · calibrated p 0.858 | 1.8 EB05 1.8 · IC025 +0.8 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled adverse reaction exact term | age-adj. PRR 1.8 · serious PRR 1.8 | NCT05098938: 1/504 (0.2%) on Acyclovir |
| Dyspnoea (shortness of breath) | 3,570 | 1.2 1.1–1.2ROR 1.2 · calibrated p 0.421 | 1.2 EB05 1.1 · IC025 +0.2 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | age-adj. PRR 1.0 · serious PRR 1.0 | not reported in cached trials |
| Asthenia (weakness) | 3,310 | 1.6 1.6–1.7ROR 1.7 · calibrated p 0.738 | 1.6 EB05 1.6 · IC025 +0.6 vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Not in label — unassessed | age-adj. PRR 1.3 · serious PRR 1.3 | not reported in cached trials |
| Headache | 3,221 | 0.9 0.9–1.0ROR 0.9 · calibrated p 0.273 | 1.0 EB05 0.9 · IC025 -0.1 PRR-only: not supported by EBGM or IC vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: only this drug | Labeled adverse reaction exact term | age-adj. PRR 1.0 · serious PRR 1.1 · ♀ 71% (drug 50%) | NCT05098938: 8/504 (1.6%) on Acyclovir; 2/497 (0.4%) control |
| Neutropenia (low neutrophils (infection-fighting cells)) | 3,210 | 4.5 4.3–4.6ROR 4.6 · calibrated p 0.288 | 4.4 EB05 4.2 · IC025 +2.1 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: PRR 41.1 (33.6–50.3) | Not in label — unassessed | age-adj. PRR 4.3 · serious PRR 3.3 | not reported in cached trials |
| White blood cell count decreased | 3,178 | 5.5 5.4–5.7ROR 5.7 · calibrated p 0.173 | 5.4 EB05 5.2 · IC025 +2.4 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: PRR 80.6 (60.8–106.8) | Labeled (related wording) related wording | age-adj. PRR 4.7 · serious PRR 4.2 | not reported in cached trials |
| Platelet count decreased | 3,064 | 5.4 5.3–5.6ROR 5.6 · calibrated p 0.182 | 5.3 EB05 5.2 · IC025 +2.3 3/3 methods agree vs other Herpes Simplex Virus Nucleoside Analog DNA Polymerase Inhibitors: PRR 33.7 (27.9–40.6) | Labeled (related wording) related wording | age-adj. PRR 4.7 · serious PRR 4.1 | not reported in cached trials |
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.
- Sensitisation — n=159, PRR 48.3
- Ejection fraction — n=117, PRR 46.1
- Encephalitis herpes — n=91, PRR 41.6
- Ophthalmic herpes simplex — n=80, PRR 29.8
- Engraftment syndrome — n=76, PRR 27.3
- Light chain analysis increased — n=125, PRR 25.5
- Polycystic ovaries — n=160, PRR 20.8
- Plasmacytoma — n=154, PRR 16.4
- Plasma cell myeloma recurrent — n=267, PRR 16.3
- Acute graft versus host disease in intestine — n=112, PRR 15.9
✓ A hand-written Bradford Hill causality assessment exists for this drug: Acyclovir ↔ Acute kidney injury.
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 Acyclovir?
In FDA FAERS, the most frequently co-reported reaction terms for Acyclovir are fatigue, diarrhoea, pneumonia, nausea, pyrexia, rash. 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 Acyclovir have an FDA boxed warning?
No. The FDA label retrieved for Acyclovir has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Acyclovir 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 0990b625-5dfe-4810-b5b4-ac5948599e79, effective 20260427; matched on
openfda.generic_name.exact:"ACYCLOVIR" AND openfda.product_type:"HUMAN PRESCRIPTION DRUG") - 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, 1,234 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 - ClinicalTrials.gov API v2 (query
ACYCLOVIR, results-bearing studies sorted by enrollment)
Page generated 2026-10-14. 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.