Pharmacologic class (EPC) · 5 drug pages

Purine antimetabolite: adverse event reports filed with FDA

49,725 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.

49,725
reports across the class: 0.2% of all reports; 4,791
reports, 12 months to June 2026: 5,283 in the 12 months before; 90.3%
marked serious by the reporter: 57.4% across all reports; 5
drugs with a page: brand and generic names counted separately

Purine antimetabolite 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 49,725 adverse event reports received by FDA, 0.2% of the database, from January 2004 to June 2026.

4,791 reports arrived in the 12 months to June 2026, close to the 5,283 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 90.3% of the class's reports are marked serious, 14.2% record death among the outcomes and 31.9% record hospitalisation, as reported.

Across the class the reactions recorded most often are drug ineffective (18.5%), off label use (13.1%) and drug intolerance (7.7%). 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
Azathioprine	generic	33,639	2,890	94.7%	Drug ineffective
MavencladCladribine	brand	6,763	1,128	67.2%	Fatigue
ImuranAzathioprine	brand	5,749	407	87.3%	Drug ineffective
Cladribine	generic	2,083	200	96.2%	Off label use
Azathioprine sodium	generic	1,491	166	99.3%	Off label use

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 expected18.5%9,176
Off label useused for a purpose or in a way not on the label13.1%6,507
Drug intolerancethe medicine was not tolerated7.7%3,845
Condition aggravatedthe condition being treated got worse7.3%3,631
Rheumatoid arthritisrheumatoid arthritis, an inflammatory joint disease6.5%3,231
Fatiguetiredness6.5%3,211
Nauseafeeling sick6.3%3,142
Pneumonialung infection6.2%3,088
Arthralgiajoint pain6%3,008
Treatment failurethe treatment did not work6%2,993
Drug hypersensitivityan allergic-type reaction to a medicine5.8%2,884
Headachehead pain5.6%2,785
Diarrhoealoose or frequent stools5.4%2,678
Rashskin rash5.3%2,624
Painpain, site not specified5%2,468
Product use in unapproved indicationused for a purpose not on the label4.9%2,448
Dyspnoeashortness of breath4.7%2,338
Pyrexiafever4.6%2,301
Pain in extremitypain in an arm or leg4.6%2,295
Joint swellinga swollen joint4.5%2,232
Maternal exposure during pregnancythe mother took the medicine during pregnancy4.4%2,172
Hypersensitivityan allergic-type reaction4.4%2,170
Vomitingbeing sick4.1%2,044
Malaisegeneral feeling of being unwell4.1%2,037
Therapeutic product effect decreased3.9%1,951

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

Death14.2%7,083

Life-threatening9%4,473

Hospitalisation (initial or prolonged)31.9%15,862

Disability5.2%2,596

Congenital anomaly4.2%2,067

Other serious71.8%35,696

Not serious9.7%4,815

Patient age

Under 20.7%349

2 to 111.8%905

12 to 172.4%1,218

18 to 4426.8%13,336

45 to 6423.5%11,709

65 to 748.6%4,268

75 and over2.7%1,361

Age not given33.3%16,579

Who reported

Physician29.6%14,738

Pharmacist1.8%912

Other health professional47.3%23,529

Lawyer0.1%35

Consumer or non-health professional18.3%9,117

Not given2.8%1,394

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 Purine antimetabolite reports

Which drugs are in the Purine antimetabolite class on this site?

Azathioprine, Mavenclad, Imuran, Cladribine and Azathioprine sodium. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

49,725 reports through June 2026, 4,791 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 (18.5%), off label use (13.1%), drug intolerance (7.7%), condition aggravated (7.3%) and rheumatoid arthritis (6.5%).

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.