Pharmacologic class (EPC) · 3 drug pages

Nitroimidazole antimicrobial: adverse event reports filed with FDA

32,128 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.

32,128
reports across the class: 0.2% of all reports; 1,897
reports, 12 months to June 2026: 2,087 in the 12 months before; 84.2%
marked serious by the reporter: 57.4% across all reports; 3
drugs with a page: brand and generic names counted separately

Nitroimidazole antimicrobial is a pharmacologic class (an FDA Established Pharmacologic Class) with 3 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 32,128 adverse event reports received by FDA, 0.2% of the database, from January 2004 to June 2026.

1,897 reports arrived in the 12 months to June 2026, close to the 2,087 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 84.2% of the class's reports are marked serious, 8.9% record death among the outcomes and 37.3% record hospitalisation, as reported.

Across the class the reactions recorded most often are drug ineffective (11.5%), drug hypersensitivity (9.1%) and nausea (8.6%). 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
Metronidazole	generic	24,332	1,694	90.1%	Drug ineffective
FlagylMetronidazole	brand	6,804	112	63.1%	Drug hypersensitivity
PyleraBismuth subcitrate potassium, metronidazole, and tetracycline hydrochloride	brand	992	91	83.5%	Nausea

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 expected11.5%3,706
Drug hypersensitivityan allergic-type reaction to a medicine9.1%2,917
Nauseafeeling sick8.6%2,764
Off label useused for a purpose or in a way not on the label5.9%1,887
Vomitingbeing sick5.7%1,836
Diarrhoealoose or frequent stools5.4%1,722
Headachehead pain4.9%1,587
Abdominal painstomach or belly pain4.8%1,527
Pyrexiafever4.7%1,499
Dizzinesslight-headedness or unsteadiness4.1%1,303
Malaisegeneral feeling of being unwell3.5%1,131
Fatiguetiredness3.5%1,116
Painpain, site not specified3.2%1,037
Rashskin rash3.2%1,019
Condition aggravatedthe condition being treated got worse3%959
Dyspnoeashortness of breath2.7%866
Pruritusitching2.6%847
Drug interactionan interaction between medicines2.6%834
Macular degenerationa disease of the central retina2.6%834
Weight decreasedweight loss2.5%794
Anaemialow red blood cells2.5%791
Paraesthesiatingling or pins and needles2.4%780
Erythemaskin redness2.4%778
Clostridium difficile infection2.4%766
Constipationconstipation2.4%764

Solid bar: share of all class reports. Hollow bar: the median share across the 3 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death8.9%2,863

Life-threatening8.1%2,618

Hospitalisation (initial or prolonged)37.3%11,999

Disability4.8%1,533

Congenital anomaly0.8%252

Other serious59.1%18,977

Not serious15.8%5,073

Patient age

Under 20.9%282

2 to 111.6%516

12 to 171.9%598

18 to 4422%7,076

45 to 6423%7,404

65 to 7413.3%4,264

75 and over12.1%3,875

Age not given25.3%8,113

Who reported

Physician27.2%8,739

Pharmacist5.9%1,901

Other health professional40.5%13,018

Lawyer0.3%87

Consumer or non-health professional20.6%6,621

Not given5.5%1,762

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 Nitroimidazole antimicrobial reports

Which drugs are in the Nitroimidazole antimicrobial class on this site?

Metronidazole, Flagyl and Pylera. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

32,128 reports through June 2026, 1,897 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 (11.5%), drug hypersensitivity (9.1%), nausea (8.6%), off label use (5.9%) and vomiting (5.7%).

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.