Drugs › Herpes simplex virus nucleoside analog DNA polymerase inhibitor
Generic name
Acyclovir: adverse event reports filed with FDA
11,095 reports list it as a suspect or interacting product, 2004–2026. Class: Herpes simplex virus nucleoside analog DNA polymerase inhibitor. Also reported as Acyclovir Caps, Acyclovir /00587301/, Acyclovir 800mg.
- 11,095
- reports as suspect product
- 0.1% of all reports · about 493 a year
- 950
- reports, 12 months to June 2026
- 1,247 in the 12 months before
- 91.2%
- marked serious by the reporter
- 78.9% across the class
- 16.3%
- record death among outcomes, as reported
- 1,803 reports · not verified by FDA
Between January 2004 and June 2026, 11,095 adverse event reports received by FDA list acyclovir, a generic name as a suspect or interacting product. Reports that mention it only as a concomitant medication (100,542) are left out of every figure here.
In the 12 months to June 2026, 950 reports listed it, down 24% from 1,247 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 493 reports a year and 0.1% of the 20,646,523 reports in the database, and 37.2% of the reports for the herpes simplex virus nucleoside analog DNA polymerase inhibitor class. How many people take it is not in the data, so a count is not a rate of occurrence.
The reactions recorded most often are drug ineffective (12.5%), acute kidney injury (7.9%) and off label use (6.5%). A report can list several reactions, so shares add to more than 100%; 1,932 different terms appear across these reports. Drug ineffective is recorded in 12.5% of these reports, about the same share as in the median herpes simplex virus nucleoside analog DNA polymerase inhibitor drug (12.5%).
91.2% of the reports are marked serious by the reporter (78.9% across the class); 16.3% record death among the outcomes and 42.7% record hospitalisation, as reported. 40.2% of the reports came from other health professionals, and the largest patient age group is 45 to 64 (22.3%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
Reports by month, five years
Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.
By year received
2026 covers reports received through June 2026 only.
Reactions recorded in the reports
share of Acyclovir reports recording the termmedian drug in herpes simplex virus nucleoside analog dna polymerase inhibitor
- Drug ineffectivethe medicine did not work as expected12.5%1,383
- Acute kidney injurysudden loss of kidney function7.9%876
- Off label useused for a purpose or in a way not on the label6.5%720
- Headachehead pain4.6%515
- Pyrexiafever4.3%472
- Condition aggravatedthe condition being treated got worse4.2%467
- Neurotoxicity4%448
- Nauseafeeling sick3.7%415
- Confusional stateconfusion3.5%388
- Dyspnoeashortness of breath3.3%364
- Drug interactionan interaction between medicines2.9%327
- Rashskin rash2.9%319
- Fatiguetiredness2.8%310
- Diarrhoealoose or frequent stools2.8%309
- Deaththe patient died; cause not stated by this term2.7%300
- Drug resistance2.7%300
- Dizzinesslight-headedness or unsteadiness2.5%276
- Herpes zostershingles2.3%252
- Renal failurekidney failure2.3%250
- Pneumonialung infection2.2%249
- Encephalopathy2.2%247
- Thrombocytopenialow platelets2.2%246
- Product use in unapproved indicationused for a purpose not on the label2.2%241
- Malaisegeneral feeling of being unwell2.1%234
- Pruritusitching2.1%233
- Hypertensionhigh blood pressure2%225
- Multiple organ dysfunction syndromeseveral organs failing2%217
- Hypotensionlow blood pressure1.9%213
- Renal impairmentreduced kidney function1.9%213
- Vomitingbeing sick1.9%208
Top 30 of 1,932 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 5 drugs in the herpes simplex virus nucleoside analog dna polymerase inhibitor class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Outcomes recorded
Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 29,855 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."
Patients and reporters
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 28.7% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Herpes zoster | 1,044 | 9.4% |
| Antiviral prophylaxis | 600 | 5.4% |
| Herpes simplex | 562 | 5.1% |
| Prophylaxis | 552 | 5% |
| Encephalitis | 197 | 1.8% |
| Infection prophylaxis | 192 | 1.7% |
The indication field is filled in by the reporter and is often blank; shares are of all 11,095 reports.
Drugs most often listed in the same reports
| Drug (any role in the report) | Reports | Share of Acyclovir reports |
|---|---|---|
| Dexamethasone | 1,143 | 10.3% |
| Prednisone | 895 | 8.1% |
| Cyclophosphamide | 832 | 7.5% |
| Methylprednisolone | 799 | 7.2% |
| Vancomycin | 628 | 5.7% |
| Mycophenolate mofetil | 620 | 5.6% |
| Acetaminophen | 607 | 5.5% |
| Ceftriaxone | 579 | 5.2% |
| Prednisolone | 570 | 5.1% |
| Fluconazole | 560 | 5% |
Other products listed in reports where Acyclovir is a suspect product, whatever their own role. Co-listing means the two were recorded together; it says nothing about either product's part in the event. Only the 2,500 most-reported names are counted here.
In context
| Measure | Acyclovir | Herpes simplex virus nucleoside analog DNA polymerase inhibitor | All reports |
|---|---|---|---|
| Reports as suspect product | 11,095 | 29,855 | 20,646,523 |
| Share of that pool | — | 37.2% | 0.1% |
| Reports, latest 12 months | 950 | — | 1,332,454 |
| Marked serious | 91.2% | 78.9% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 163 | 88 | 91 |
| Hospitalisation recorded, per 1,000 reports | 427 | 398 | 213 |
| Consumer-filed share | 16.9% | 30.9% | 45.8% |
| Top term, share of reports | Drug ineffective 12.5% | median 12.5% | 6.3% |
Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."
Other drugs in the herpes simplex virus nucleoside analog dna polymerase inhibitor class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Valtrex | brand | 7,793 | 154 | 55.1% |
| Valacyclovir hydrochloride | generic | 5,237 | 773 | 92.4% |
| Valacyclovir | generic | 3,307 | 312 | 72.5% |
| Zovirax | brand | 2,423 | 14 | 78.6% |
Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.
Questions about Acyclovir reports
How many adverse event reports has FDA received for Acyclovir?
11,095 reports list Acyclovir as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 950 of them arrived in the latest 12 months. Another 100,542 list it only as a concomitant medication.
What reactions are recorded in Acyclovir reports?
drug ineffective (12.5%), acute kidney injury (7.9%), off label use (6.5%), headache (4.6%) and pyrexia (4.3%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Acyclovir was responsible.
How serious are the reports?
91.2% are marked serious by the reporter. Among the outcomes recorded, 16.3% of reports include death and 42.7% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
other health professional (40.2%), physician (31.9%) and consumer or non-health professional (16.9%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Acyclovir rising?
950 reports in the 12 months to June 2026, down 24% from 1,247 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Acyclovir was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Acyclovir?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. See the guide on how to report.
Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Acyclovir as a suspect or interacting product; reports listing it only as a concomitant medication (100,542) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.
Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.