Pharmacologic class (EPC) · 5 drug pages

Herpes simplex virus nucleoside analog DNA polymerase inhibitor: adverse event reports filed with FDA

29,855 reports list a drug in this class as a suspect or interacting product, 2004–2026.

Read first · FDA's statement on these data

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product. openFDA, FDA

FDA adds: "There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event." The information in these reports "cannot be used to estimate the incidence of these events."

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

29,855
reports across the class: 0.1% of all reports; 2,203
reports, 12 months to June 2026: 2,601 in the 12 months before; 78.9%
marked serious by the reporter: 57.4% across all reports; 5
drugs with a page: brand and generic names counted separately

Herpes simplex virus nucleoside analog DNA polymerase inhibitor is a pharmacologic class (an FDA Established Pharmacologic Class) with 5 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 29,855 adverse event reports received by FDA, 0.1% of the database, from January 2004 to June 2026.

2,203 reports arrived in the 12 months to June 2026, down 15% from 2,601 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 78.9% of the class's reports are marked serious, 8.8% record death among the outcomes and 39.8% record hospitalisation, as reported.

Across the class the reactions recorded most often are drug ineffective (11.8%), acute kidney injury (5.6%) and off label use (4.4%). The class median share shown beside each term is the middle value across the member drugs; it is the comparison used on every drug page in this class.

The members table is 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."

Drugs in the class

Drug	Name type	Reports	Latest 12 months	Marked serious	Top term recorded
Acyclovir	generic	11,095	950	91.2%	Drug ineffective
ValtrexValacyclovir hydrochloride	brand	7,793	154	55.1%	Drug ineffective
Valacyclovir hydrochloride	generic	5,237	773	92.4%	Drug ineffective
Valacyclovir	generic	3,307	312	72.5%	Drug ineffective
ZoviraxAcyclovir	brand	2,423	14	78.6%	Drug ineffective

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."

Reports by month, five years

FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

Reactions recorded across the class

share of class reports recording the termmedian drug in the class

Drug ineffectivethe medicine did not work as expected11.8%3,522
Acute kidney injurysudden loss of kidney function5.6%1,684
Off label useused for a purpose or in a way not on the label4.4%1,316
Nauseafeeling sick4.4%1,304
Headachehead pain4.2%1,268
Pyrexiafever3.8%1,127
Dizzinesslight-headedness or unsteadiness3.3%980
Rashskin rash3.2%960
Confusional stateconfusion3.2%941
Condition aggravatedthe condition being treated got worse3%896
Vomitingbeing sick2.9%878
Diarrhoealoose or frequent stools2.7%818
Neurotoxicity2.7%817
Renal failure acute2.6%791
Altered state of consciousness2.6%790
Dyspnoeashortness of breath2.5%757
Fatiguetiredness2.5%747
Malaisegeneral feeling of being unwell2.3%696
Encephalopathy2.3%694
Herpes zostershingles2.3%678
Painpain, site not specified2.3%672
Renal impairmentreduced kidney function2.1%627
Blood creatinine increasedraised creatinine, a kidney test2.1%614
Pruritusitching2%603
Drug interactionan interaction between medicines1.9%579

Solid bar: share of all class reports. Hollow bar: the median share across the 5 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death8.8%2,639

Life-threatening6.7%2,004

Hospitalisation (initial or prolonged)39.8%11,877

Disability2.3%682

Congenital anomaly0.8%240

Other serious51.3%15,311

Not serious21.1%6,299

Patient age

Under 21.4%405

2 to 112.5%739

12 to 171.7%500

18 to 4414.8%4,416

45 to 6421.2%6,320

65 to 7413.2%3,941

75 and over13.1%3,909

Age not given32.2%9,625

Who reported

Physician32.7%9,754

Pharmacist9.9%2,960

Other health professional24.2%7,216

Lawyer0.1%17

Consumer or non-health professional30.9%9,217

Not given2.3%691

Grey bar: all 20,646,523 reports in the database. Outcome flags are as the reporter set them and are not verified by FDA.

Questions about Herpes simplex virus nucleoside analog DNA polymerase inhibitor reports

Which drugs are in the Herpes simplex virus nucleoside analog DNA polymerase inhibitor class on this site?

Acyclovir, Valtrex, Valacyclovir hydrochloride, Valacyclovir and Zovirax. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

29,855 reports through June 2026, 2,203 of them in the latest 12 months. A report listing two drugs of the class counts once for each.

What reactions are recorded most often?

drug ineffective (11.8%), acute kidney injury (5.6%), off label use (4.4%), nausea (4.4%) and headache (4.2%).

Can the members table be used to rank the drugs?

No. 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." Drugs differ in how many people take them, in the conditions they treat, in time on the market and in how diligently reports are collected.

How do I report an adverse event?

Through FDA MedWatch (Form FDA 3500, or 1-800-FDA-1088) or to the manufacturer. 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 class is the Established Pharmacologic Class most often attached to a drug's reports by openFDA's label harmonisation, or from the NDC Directory where reports carry none. 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.