Drugs › Nucleoside analog antiviral
Brand name · Trifluridine and tipiracil
Lonsurf: adverse event reports filed with FDA
10,262 reports list it as a suspect or interacting product, 2015–2026. Class: Nucleoside analog antiviral.
- 10,262
- reports as suspect product
- 0.1% of all reports · about 940 a year
- 547
- reports, 12 months to June 2026
- 548 in the 12 months before
- 78.4%
- marked serious by the reporter
- 67.2% across the class
- 40.3%
- record death among outcomes, as reported
- 4,140 reports · not verified by FDA
10,262 adverse event reports received by FDA list the brand name Lonsurf (trifluridine and tipiracil) as a suspect or interacting product, from August 2015 to June 2026. A further 402 reports list it only as a concomitant medication, and those are not counted in the figures on this page.
In the 12 months to June 2026, 547 reports listed it, close to the 548 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 940 reports a year and 0.1% of the 20,646,523 reports in the database, and 17.2% of the reports for the nucleoside analog antiviral class. How many people take it is not in the data, so a count is not a rate of occurrence.
Reporters most often recorded death (29.6%), disease progression (17.2%) and fatigue (12.9%). A report can list several reactions, so shares add to more than 100%; 713 different terms appear across these reports. Death is recorded in 29.6% of these reports, a larger share than in the median nucleoside analog antiviral drug (15.3%).
78.4% of the reports are marked serious by the reporter (67.2% across the class); 40.3% record death among the outcomes and 27.6% record hospitalisation, as reported. 46% of the reports came from consumers, and the largest patient age group is 45 to 64 (31.8%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
Reports by month, five years
Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.
By year received
2026 covers reports received through June 2026 only.
Reactions recorded in the reports
share of Lonsurf reports recording the termmedian drug in nucleoside analog antiviral
- Deaththe patient died; cause not stated by this term29.6%3,038
- Disease progressionthe disease advanced17.2%1,766
- Fatiguetiredness12.9%1,324
- Nauseafeeling sick11.2%1,149
- Diarrhoealoose or frequent stools9.4%966
- Decreased appetitereduced appetite6.3%646
- Vomitingbeing sick6%613
- Astheniaweakness or lack of energy4.7%484
- White blood cell count decreasedlow white cell count4.7%481
- Drug ineffectivethe medicine did not work as expected3.4%350
- Anaemialow red blood cells3.4%344
- Constipationconstipation3.2%327
- Dehydrationdehydration3.1%322
- Neutropenialow neutrophils, a type of white blood cell3.1%322
- Inappropriate schedule of product administrationthe product was taken at the wrong times3%312
- Weight decreasedweight loss3%312
- Abdominal painstomach or belly pain3%305
- Off label useused for a purpose or in a way not on the label2.5%255
- Malaisegeneral feeling of being unwell2.5%253
- Painpain, site not specified2.5%253
- Abdominal pain upperupper stomach pain2.4%247
- Pyrexiafever2.3%238
- Platelet count decreasedlow platelet count2.2%222
- Dyspnoeashortness of breath2%210
- Haemoglobin decreasedlow haemoglobin1.8%189
- Cytopenia1.7%175
- Alopeciahair loss1.7%173
- Dizzinesslight-headedness or unsteadiness1.7%173
- Urinary tract infectionbladder or urinary infection1.6%163
Top 30 of 713 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 2 drugs in the nucleoside analog antiviral class; it describes the reports, not the patients. 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."
Outcomes recorded
Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 59,646 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."
Patients and reporters
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 79.6% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Colon cancer | 3,975 | 38.7% |
| Rectal cancer | 1,233 | 12% |
| Colorectal cancer metastatic | 1,179 | 11.5% |
| Colorectal cancer | 375 | 3.7% |
| Colon cancer metastatic | 328 | 3.2% |
| Rectosigmoid cancer | 247 | 2.4% |
The indication field is filled in by the reporter and is often blank; shares are of all 10,262 reports.
Drugs most often listed in the same reports
| Drug (any role in the report) | Reports | Share of Lonsurf reports |
|---|---|---|
| Ondansetron | 708 | 6.9% |
| Gabapentin | 636 | 6.2% |
| Amlodipine | 565 | 5.5% |
| Lisinopril | 539 | 5.3% |
| Oxycodone | 529 | 5.2% |
| Zofran | 513 | 5% |
| Omeprazole | 437 | 4.3% |
| Bevacizumab | 405 | 3.9% |
| Avastin | 394 | 3.8% |
| Eliquis | 349 | 3.4% |
Other products listed in reports where Lonsurf is a suspect product, whatever their own role. Co-listing means the two were recorded together; it says nothing about either product's part in the event. Only the 2,500 most-reported names are counted here.
In context
| Measure | Lonsurf | Nucleoside analog antiviral | All reports |
|---|---|---|---|
| Reports as suspect product | 10,262 | 59,646 | 20,646,523 |
| Share of that pool | — | 17.2% | 0.1% |
| Reports, latest 12 months | 547 | — | 1,332,454 |
| Marked serious | 78.4% | 67.2% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 403 | 117 | 91 |
| Hospitalisation recorded, per 1,000 reports | 276 | 238 | 213 |
| Consumer-filed share | 46% | 41.8% | 45.8% |
| Top term, share of reports | Death 29.6% | median 15.3% | 4.1% |
Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. 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."
Other drugs in the nucleoside analog antiviral class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Ribavirin | generic | 49,384 | 83 | 64.9% |
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." A brand and its generic are separate rows because reporters name them separately.
Questions about Lonsurf reports
How many adverse event reports has FDA received for Lonsurf?
10,262 reports list Lonsurf as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 547 of them arrived in the latest 12 months. Another 402 list it only as a concomitant medication.
What reactions are recorded in Lonsurf reports?
death (29.6%), disease progression (17.2%), fatigue (12.9%), nausea (11.2%) and diarrhoea (9.4%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Lonsurf was responsible.
How serious are the reports?
78.4% are marked serious by the reporter. Among the outcomes recorded, 40.3% of reports include death and 27.6% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
consumer or non-health professional (46%), other health professional (22.6%) and pharmacist (16.3%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Lonsurf rising?
547 reports in the 12 months to June 2026, close to the 548 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Lonsurf was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Lonsurf?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. 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 report counts here when it lists Lonsurf as a suspect or interacting product; reports listing it only as a concomitant medication (402) are excluded. 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.