Pharmacologic class (EPC) · 6 drug pages

Dihydrofolate reductase inhibitor antibacterial: adverse event reports filed with FDA

41,847 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.

41,847
reports across the class: 0.2% of all reports; 3,516
reports, 12 months to June 2026: 4,493 in the 12 months before; 89.3%
marked serious by the reporter: 57.4% across all reports; 6
drugs with a page: brand and generic names counted separately

Dihydrofolate reductase inhibitor antibacterial is a pharmacologic class (an FDA Established Pharmacologic Class) with 6 drug pages on this site. Together those drugs are listed as a suspect or interacting product in 41,847 adverse event reports received by FDA, 0.2% of the database, from January 2004 to June 2026.

3,516 reports arrived in the 12 months to June 2026, down 22% from 4,493 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. 89.3% of the class's reports are marked serious, 14.3% record death among the outcomes and 53% record hospitalisation, as reported.

Across the class the reactions recorded most often are rash (12%), drug ineffective (12%) and pyrexia (11.8%). 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
BactrimSulfamethoxazole and trimethoprim	brand	16,598	1,135	85.3%	Drug hypersensitivity
Sulfamethoxazole, trimethoprim	generic	9,960	1,571	96.7%	Drug ineffective
Sulfamethoxazole and trimethoprim	generic	9,070	402	87.6%	Rash
Trimethoprim	generic	4,093	229	94.8%	Headache
Bactrim DSSulfamethoxazole and trimethoprim	brand	1,550	59	78.1%	Drug hypersensitivity
SulfatrimSulfamethoxazole and trimethoprim	brand	576	120	98.1%	Dyspnoea

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

Rashskin rash12%5,042
Drug ineffectivethe medicine did not work as expected12%5,012
Pyrexiafever11.8%4,934
Drug hypersensitivityan allergic-type reaction to a medicine10.5%4,389
Pruritusitching9.2%3,866
Dyspnoeashortness of breath8.8%3,683
Fatiguetiredness8.6%3,587
Off label useused for a purpose or in a way not on the label8.5%3,575
Painpain, site not specified8.5%3,557
Hypersensitivityan allergic-type reaction8.1%3,408
Nauseafeeling sick7.5%3,132
Infectionan infection, type not specified7.2%3,002
Joint swellinga swollen joint7.1%2,975
Arthralgiajoint pain7%2,949
Confusional stateconfusion6.9%2,908
Vomitingbeing sick6.9%2,899
Peripheral swellingswelling of the arms or legs6.7%2,784
Headachehead pain6.6%2,775
Diarrhoealoose or frequent stools6.6%2,757
Sinusitissinus infection6.5%2,732
Swellingswelling6.4%2,689
Folliculitis6.4%2,658
Impaired healingslow healing6.3%2,654
Stomatitissore mouth6.3%2,640
Lower respiratory tract infectiona chest infection6.2%2,597

Solid bar: share of all class reports. Hollow bar: the median share across the 6 member drugs, the reference used on each member's page. One report can record several terms.

Outcomes, patients and reporters

Outcomes recorded

Death14.3%5,971

Life-threatening14.2%5,930

Hospitalisation (initial or prolonged)53%22,160

Disability9.4%3,951

Congenital anomaly2.8%1,163

Other serious57.7%24,163

Not serious10.7%4,462

Patient age

Under 20.8%338

2 to 112.3%973

12 to 171.9%810

18 to 4420.4%8,527

45 to 6422.9%9,582

65 to 7415.5%6,476

75 and over13.1%5,476

Age not given23.1%9,665

Who reported

Physician33.6%14,058

Pharmacist11.1%4,647

Other health professional38.2%15,997

Lawyer0.1%43

Consumer or non-health professional14.3%5,977

Not given2.7%1,125

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 Dihydrofolate reductase inhibitor antibacterial reports

Which drugs are in the Dihydrofolate reductase inhibitor antibacterial class on this site?

Bactrim, Sulfamethoxazole, trimethoprim, Sulfamethoxazole and trimethoprim, Trimethoprim, Bactrim DS and Sulfatrim. Class membership comes from the pharmacologic class (EPC) on the drug's FDA label.

How many reports does the class have?

41,847 reports through June 2026, 3,516 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?

rash (12%), drug ineffective (12%), pyrexia (11.8%), drug hypersensitivity (10.5%) and pruritus (9.2%).

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.