Pharmacologic class (EPC) · 3 drug pages

Xanthine oxidase inhibitor: adverse event reports filed with FDA

27,590 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.

27,590
reports across the class: 0.1% of all reports; 1,405
reports, 12 months to June 2026: 1,925 in the 12 months before; 87.7%
marked serious by the reporter: 57.4% across all reports; 3
drugs with a page: brand and generic names counted separately

Xanthine oxidase inhibitor 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 27,590 adverse event reports received by FDA, 0.1% of the database, from January 2004 to June 2026.

1,405 reports arrived in the 12 months to June 2026, down 27% from 1,925 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 87.7% of the class's reports are marked serious, 13% record death among the outcomes and 51.8% record hospitalisation, as reported.

Across the class the reactions recorded most often are drug reaction with eosinophilia and systemic symptoms (11.5%), acute kidney injury (6.1%) and rash (5.8%). 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
Allopurinol	generic	22,514	1,238	95.1%	Drug reaction with eosinophilia and systemic symptoms
UloricFebuxostat	brand	3,100	13	29.4%	Gout
Febuxostat	generic	1,976	154	95.2%	Acute kidney injury

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 reaction with eosinophilia and systemic symptomsDRESS, a severe reaction with rash, fever and organ involvement11.5%3,173
Acute kidney injurysudden loss of kidney function6.1%1,695
Rashskin rash5.8%1,612
Pyrexiafever4.5%1,242
Drug interactionan interaction between medicines4.3%1,179
Dyspnoeashortness of breath4.2%1,164
Off label useused for a purpose or in a way not on the label4.2%1,148
Drug ineffectivethe medicine did not work as expected4.1%1,124
Diarrhoealoose or frequent stools4%1,096
Toxic epidermal necrolysisa severe skin reaction with peeling3.9%1,073
Pruritusitching3.9%1,067
Nauseafeeling sick3.8%1,056
Goutgout3.8%1,042
Stevens-Johnson syndromea severe skin and mucous-membrane reaction3.5%955
Anaemialow red blood cells3.2%890
Condition aggravatedthe condition being treated got worse3.2%878
Vomitingbeing sick2.9%795
Fatiguetiredness2.8%768
Renal failurekidney failure2.8%767
Abdominal painstomach or belly pain2.7%739
Hypotensionlow blood pressure2.5%699
General physical health deteriorationgeneral decline in health2.5%690
Sepsisa severe body-wide response to infection2.5%688
Oedema peripheralswelling of the legs, ankles or hands2.4%667
Dizzinesslight-headedness or unsteadiness2.4%665

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

Death13%3,593

Life-threatening9.5%2,634

Hospitalisation (initial or prolonged)51.8%14,302

Disability3.3%913

Congenital anomaly0.9%237

Other serious50.1%13,833

Not serious12.3%3,393

Patient age

Under 20.1%40

2 to 110.5%128

12 to 170.5%146

18 to 447.7%2,111

45 to 6420.5%5,664

65 to 7419.9%5,480

75 and over28.1%7,754

Age not given22.7%6,267

Who reported

Physician37.7%10,398

Pharmacist10.5%2,884

Other health professional33%9,108

Lawyer0.3%91

Consumer or non-health professional13.7%3,767

Not given4.9%1,342

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 Xanthine oxidase inhibitor reports

Which drugs are in the Xanthine oxidase inhibitor class on this site?

Allopurinol, Uloric and Febuxostat. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

27,590 reports through June 2026, 1,405 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 reaction with eosinophilia and systemic symptoms (11.5%), acute kidney injury (6.1%), rash (5.8%), pyrexia (4.5%) and drug interaction (4.3%).

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.