Generic name
Treosulfan: adverse event reports filed with FDA
2,107 reports list it as a suspect or interacting product, 2004–2026. Also reported as Treosulfan Injection.
- 2,107
- reports as suspect product
- 0% of all reports · about 94 a year
- 336
- reports, 12 months to June 2026
- 273 in the 12 months before
- 98.7%
- marked serious by the reporter
- 57.4% across all reports
- 21.6%
- record death among outcomes, as reported
- 455 reports · not verified by FDA
2,107 adverse event reports received by FDA list treosulfan, a generic name as a suspect or interacting product, from January 2004 to June 2026. A further 542 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, 336 reports listed it, up 23% from 273 in 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 94 reports a year and 0% of the 20,646,523 reports in the database. How many people take it is not in the data, so a count is not a rate of occurrence.
Reporters most often recorded off label use (24.8%), cytomegalovirus infection reactivation (11.3%) and cytomegalovirus infection (11.1%). A report can list several reactions, so shares add to more than 100%; 558 different terms appear across these reports. Off label use is recorded in 24.8% of these reports, against 4.1% of all reports in the database.
98.7% of the reports are marked serious by the reporter; 21.6% record death among the outcomes and 16.8% record hospitalisation, as reported. 56.8% of the reports came from other health professionals, and the largest patient age group is 2 to 11 (27.1%). 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 Treosulfan reports recording the termall reports in the database
- Off label useused for a purpose or in a way not on the label24.8%523
- Cytomegalovirus infection reactivation11.3%238
- Cytomegalovirus infection11.1%234
- Mucosal inflammation10.9%229
- Adenovirus infection9.7%205
- Acute graft versus host disease in skin8.1%170
- Product use in unapproved indicationused for a purpose not on the label7.7%163
- Drug ineffectivethe medicine did not work as expected6.8%144
- Graft versus host disease in skin6.2%130
- Acute graft versus host disease5.6%118
- Human herpesvirus 6 infection5.5%116
- Multiple organ dysfunction syndromeseveral organs failing4.9%104
- Graft versus host disease in gastrointestinal tract4.7%98
- Neutropenialow neutrophils, a type of white blood cell4.4%93
- Pyrexiafever4.2%89
- Cytomegalovirus viraemia3.7%79
- Febrile neutropeniafever with low white blood cells3.7%78
- Sepsisa severe body-wide response to infection3.7%78
- Venoocclusive liver disease3.4%72
- Acute graft versus host disease in intestine3.4%71
- Thrombocytopenialow platelets3.2%68
- Product use issuea problem in how the product was used3%64
- Acute kidney injurysudden loss of kidney function3%63
- BK virus infection2.9%61
- Staphylococcal infection2.7%56
- Diarrhoealoose or frequent stools2.6%54
- Intentional product use issuedeliberate use not as intended2.5%53
Top 30 of 558 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 share of all reports in the database; 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 20,646,523 reports. 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. 1.6% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Bone marrow conditioning regimen | 684 | 32.5% |
| Allogenic stem cell transplantation | 418 | 19.8% |
| Prophylaxis against transplant rejection | 167 | 7.9% |
| Stem cell transplant | 83 | 3.9% |
| Immunosuppressant drug therapy | 62 | 2.9% |
| Acute myeloid leukaemia | 51 | 2.4% |
The indication field is filled in by the reporter and is often blank; shares are of all 2,107 reports.
Drugs most often listed in the same reports
| Drug (any role in the report) | Reports | Share of Treosulfan reports |
|---|---|---|
| Fludarabine | 1,383 | 65.6% |
| Thiotepa | 1,151 | 54.6% |
| Mycophenolate mofetil | 795 | 37.7% |
| Cyclosporine | 718 | 34.1% |
| Cyclophosphamide | 609 | 28.9% |
| Rituximab | 533 | 25.3% |
| Tacrolimus | 457 | 21.7% |
| Methotrexate | 453 | 21.5% |
| Alemtuzumab | 418 | 19.8% |
| Fludarabine phosphate | 406 | 19.3% |
Other products listed in reports where Treosulfan 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 | Treosulfan | All reports |
|---|---|---|
| Reports as suspect product | 2,107 | 20,646,523 |
| Share of that pool | — | 0% |
| Reports, latest 12 months | 336 | 1,332,454 |
| Marked serious | 98.7% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 216 | 91 |
| Hospitalisation recorded, per 1,000 reports | 168 | 213 |
| Consumer-filed share | 1.4% | 45.8% |
| Top term, share of reports | Off label use 24.8% | 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."
Questions about Treosulfan reports
How many adverse event reports has FDA received for Treosulfan?
2,107 reports list Treosulfan as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 336 of them arrived in the latest 12 months. Another 542 list it only as a concomitant medication.
What reactions are recorded in Treosulfan reports?
off label use (24.8%), cytomegalovirus infection reactivation (11.3%), cytomegalovirus infection (11.1%), mucosal inflammation (10.9%) and adenovirus infection (9.7%). 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 Treosulfan was responsible.
How serious are the reports?
98.7% are marked serious by the reporter. Among the outcomes recorded, 21.6% of reports include death and 16.8% 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?
other health professional (56.8%), physician (38.6%) and not given (1.6%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Treosulfan rising?
336 reports in the 12 months to June 2026, up 23% from 273 in 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 Treosulfan 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 Treosulfan?
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 Treosulfan as a suspect or interacting product; reports listing it only as a concomitant medication (542) 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.