Pharmacologic class (EPC) · 19 drug pages

Nucleoside metabolic inhibitor: adverse event reports filed with FDA

313,386 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.

313,386
reports across the class: 1.5% of all reports; 22,327
reports, 12 months to June 2026: 23,447 in the 12 months before; 92.2%
marked serious by the reporter: 57.4% across all reports; 19
drugs with a page: brand and generic names counted separately

Nucleoside metabolic inhibitor is a pharmacologic class (an FDA Established Pharmacologic Class) with 19 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 313,386 adverse event reports received by FDA, 1.5% of the database, from January 2004 to June 2026.

22,327 reports arrived in the 12 months to June 2026, close to the 23,447 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 92.2% of the class's reports are marked serious, 21% record death among the outcomes and 38% record hospitalisation, as reported.

Across the class the reactions recorded most often are diarrhoea (7.6%), febrile neutropenia (6.5%) and off label use (6.3%). 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
Fluorouracil	generic	60,451	5,315	96.1%	Diarrhoea
Capecitabine	generic	51,783	3,281	83.3%	Diarrhoea
Cytarabine	generic	50,741	3,545	97.9%	Febrile neutropenia
Gemcitabine	generic	33,198	2,920	97.9%	Disease progression
XelodaCapecitabine	brand	32,279	280	73%	Diarrhoea
FludarabineFludarabine phosphate	brand	20,260	1,900	98.7%	Off label use
Azacitidine	generic	14,969	1,830	98%	Febrile neutropenia
Gemcitabine hydrochloride	generic	12,399	1,164	97.1%	Off label use
Mercaptopurine	generic	10,540	507	95.8%	Febrile neutropenia
VidazaAzacitidine	brand	9,087	358	96.9%	Death
Fludarabine phosphate	generic	8,426	419	98.5%	Off label use
Decitabine	generic	3,026	258	96.8%	Febrile neutropenia
Clofarabine	generic	2,020	77	96.5%	Febrile neutropenia
Purixan	generic	767	29	81.5%	Off label use
OnuregAzacitidine	brand	755	69	49.8%	Off label use
Pentostatin	generic	697	16	91.7%	Neutropenia
InqoviCedazuridine and decitabine	brand	677	269	81.5%	Inappropriate schedule of product administration
Nelarabine	generic	659	90	98.8%	Drug ineffective
Capecitabine 500mgCapecitabine	brand	652	0	63.3%	Death

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

Diarrhoealoose or frequent stools7.6%23,944
Febrile neutropeniafever with low white blood cells6.5%20,246
Off label useused for a purpose or in a way not on the label6.3%19,724
Neutropenialow neutrophils, a type of white blood cell5.8%18,042
Nauseafeeling sick5.8%18,021
Disease progressionthe disease advanced5.4%17,006
Deaththe patient died; cause not stated by this term5.2%16,262
Pyrexiafever4.8%15,126
Vomitingbeing sick4.5%14,131
Thrombocytopenialow platelets4.5%14,063
Drug ineffectivethe medicine did not work as expected4.1%12,904
Fatiguetiredness4%12,395
Anaemialow red blood cells3.5%11,104
Sepsisa severe body-wide response to infection2.9%9,238
Pneumonialung infection2.9%9,132
Malignant neoplasm progression2.9%8,967
Palmar-plantar erythrodysaesthesia syndrome2.6%8,219
Astheniaweakness or lack of energy2.6%8,085
Myelosuppression2.6%8,058
Neuropathy peripheralnerve damage in hands or feet2.4%7,463
Mucosal inflammation2.3%7,352
Pancytopenialow counts of all blood cells2.2%6,926
Decreased appetitereduced appetite2.1%6,657
Dyspnoeashortness of breath2.1%6,603
Abdominal painstomach or belly pain2%6,398

Solid bar: share of all class reports. Hollow bar: the median share across the 19 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death21%65,885

Life-threatening7.5%23,659

Hospitalisation (initial or prolonged)38%119,199

Disability1.4%4,442

Congenital anomaly0.1%285

Other serious55.6%174,236

Not serious7.8%24,363

Patient age

Under 20.8%2,618

2 to 113.9%12,238

12 to 172.5%7,886

18 to 449.1%28,546

45 to 6425.8%80,821

65 to 7417.8%55,895

75 and over9.5%29,672

Age not given30.5%95,710

Who reported

Physician38.4%120,248

Pharmacist5.8%18,066

Other health professional38.2%119,682

Lawyer0%123

Consumer or non-health professional11.4%35,706

Not given6.2%19,561

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 Nucleoside metabolic inhibitor reports

Which drugs are in the Nucleoside metabolic inhibitor class on this site?

Fluorouracil, Capecitabine, Cytarabine, Gemcitabine, Xeloda and Fludarabine and 13 more. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

313,386 reports through June 2026, 22,327 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?

diarrhoea (7.6%), febrile neutropenia (6.5%), off label use (6.3%), neutropenia (5.8%) and nausea (5.8%).

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.