Pharmacologic class (EPC) · 2 drug pages

Pyrimidine synthesis inhibitor: adverse event reports filed with FDA

41,974 reports list a drug in this class as a suspect or interacting product, 2011–2026.

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.

41,974
reports across the class: 0.2% of all reports; 495
reports, 12 months to June 2026: 719 in the 12 months before; 43.7%
marked serious by the reporter: 57.4% across all reports; 2
drugs with a page: brand and generic names counted separately

Pyrimidine synthesis inhibitor is a pharmacologic class (an FDA Established Pharmacologic Class) with 2 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 41,974 adverse event reports received by FDA, 0.2% of the database, from November 2011 to June 2026.

495 reports arrived in the 12 months to June 2026, down 31% from 719 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 43.7% of the class's reports are marked serious, 1.6% record death among the outcomes and 13.8% record hospitalisation, as reported.

Across the class the reactions recorded most often are alopecia (14.2%), multiple sclerosis relapse (11.9%) and diarrhoea (10.9%). 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
AubagioTeriflunomide	brand	36,990	161	40.4%	Alopecia
Teriflunomide	generic	4,984	334	68.4%	Alopecia

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

Alopeciahair loss14.2%5,976
Multiple sclerosis relapsea flare of multiple sclerosis11.9%4,981
Diarrhoealoose or frequent stools10.9%4,596
Fatiguetiredness10.7%4,485
Hypoaesthesianumbness7.3%3,049
Falla fall7.2%3,004
Headachehead pain6.8%2,843
Paraesthesiatingling or pins and needles6.4%2,707
Nauseafeeling sick6.2%2,618
Drug ineffectivethe medicine did not work as expected6%2,535
Gait disturbancedifficulty walking5.2%2,197
Painpain, site not specified5.1%2,128
Multiple sclerosis4.9%2,056
Condition aggravatedthe condition being treated got worse4.4%1,855
Depressionlow mood4%1,669
Balance disorderproblems with balance3.9%1,630
Astheniaweakness or lack of energy3.8%1,584
Pain in extremitypain in an arm or leg3.7%1,552
Memory impairmentmemory problems3.7%1,534
Dizzinesslight-headedness or unsteadiness3.6%1,531
Product dose omission issuea dose was missed3.4%1,415
Muscular weaknessmuscle weakness2.7%1,146
Malaisegeneral feeling of being unwell2.7%1,128
Rashskin rash2.7%1,115
Drug dose omissiona dose was missed2.6%1,108

Solid bar: share of all class reports. Hollow bar: the median share across the 2 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death1.6%656

Life-threatening0.7%309

Hospitalisation (initial or prolonged)13.8%5,811

Disability2.9%1,224

Congenital anomaly0.1%34

Other serious34.9%14,664

Not serious56.3%23,623

Patient age

Under 20.1%23

2 to 110%8

12 to 170%18

18 to 4415.9%6,661

45 to 6439.1%16,408

65 to 747.5%3,155

75 and over1.1%473

Age not given36.3%15,228

Who reported

Physician28.8%12,083

Pharmacist4.5%1,872

Other health professional7.5%3,131

Lawyer0%11

Consumer or non-health professional57.3%24,044

Not given2%833

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 Pyrimidine synthesis inhibitor reports

Which drugs are in the Pyrimidine synthesis inhibitor class on this site?

Aubagio and Teriflunomide. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

41,974 reports through June 2026, 495 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?

alopecia (14.2%), multiple sclerosis relapse (11.9%), diarrhoea (10.9%), fatigue (10.7%) and hypoaesthesia (7.3%).

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.