Pharmacologic class (EPC) · 3 drug pages

Antimetabolite: adverse event reports filed with FDA

8,764 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.

8,764
reports across the class: 0% of all reports; 431
reports, 12 months to June 2026: 644 in the 12 months before; 89.5%
marked serious by the reporter: 57.4% across all reports; 3
drugs with a page: brand and generic names counted separately

Antimetabolite 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 8,764 adverse event reports received by FDA, 0% of the database, from January 2004 to June 2026.

431 reports arrived in the 12 months to June 2026, down 33% from 644 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 89.5% of the class's reports are marked serious, 13.9% record death among the outcomes and 39.4% record hospitalisation, as reported.

Across the class the reactions recorded most often are febrile neutropenia (8.1%), off label use (7%) and pyrexia (5.1%). 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
Hydroxyurea	generic	4,260	326	86.8%	Off label use
HydreaHydroxyurea	brand	2,669	38	88%	Off label use
Thioguanine	generic	1,835	67	97.9%	Febrile neutropenia

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

Febrile neutropeniafever with low white blood cells8.1%706
Off label useused for a purpose or in a way not on the label7%615
Pyrexiafever5.1%444
Anaemialow red blood cells4.8%420
Drug ineffectivethe medicine did not work as expected4.7%416
Thrombocytopenialow platelets4.2%371
Fatiguetiredness3.8%329
Nauseafeeling sick3.6%312
Diarrhoealoose or frequent stools3.1%274
Neutropenialow neutrophils, a type of white blood cell3%260
Pancytopenialow counts of all blood cells2.8%249
Platelet count decreasedlow platelet count2.8%242
Vomitingbeing sick2.7%236
Headachehead pain2.6%229
Pneumonialung infection2.6%228
Skin ulceran open sore on the skin2.5%221
Deaththe patient died; cause not stated by this term2.4%213
Dyspnoeashortness of breath2.4%213
Astheniaweakness or lack of energy2.4%206
Haemoglobin decreasedlow haemoglobin2.4%206
Platelet count increased2.2%197
Intentional product use issuedeliberate use not as intended2.1%186
Product use in unapproved indicationused for a purpose not on the label2.1%181
Painpain, site not specified2%177
White blood cell count decreasedlow white cell count1.9%166

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

Death13.9%1,216

Life-threatening6.7%591

Hospitalisation (initial or prolonged)39.4%3,454

Disability1.7%151

Congenital anomaly0.6%54

Other serious62.1%5,445

Not serious10.5%919

Patient age

Under 20.9%82

2 to 117.6%662

12 to 175.5%484

18 to 4410.9%959

45 to 6414%1,230

65 to 7413.5%1,180

75 and over15.5%1,355

Age not given32.1%2,812

Who reported

Physician33.3%2,918

Pharmacist9.9%870

Other health professional32%2,808

Lawyer0%4

Consumer or non-health professional20.3%1,775

Not given4.4%389

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 Antimetabolite reports

Which drugs are in the Antimetabolite class on this site?

Hydroxyurea, Hydrea and Thioguanine. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

8,764 reports through June 2026, 431 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?

febrile neutropenia (8.1%), off label use (7%), pyrexia (5.1%), anaemia (4.8%) and drug ineffective (4.7%).

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.