Letermovir adverse event reports that FDA received
- Name type
- Generic name
What a report is
A report is not proof that the drug was the cause of the event.
FDA says:
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.
Source: openFDA, Drug Adverse Event Overview, section "Responsible use of the data". The site read the page on . The data have the reports that FDA received through .
FDA also says:
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 has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
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.
Source: openFDA, Response of the drug event API (meta.disclaimer). The site read the page on .
Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.
Drug reports received through . Device reports have a separate cutoff, 30 Sep 2026. Why a report count is not a rate.
Reports on file
From May 2018 to June 2026, FDA received 565 adverse event reports that name Letermovir. In these reports the drug is a suspect or interacting product.
In the same period, 899 further reports name it only as a concomitant medicine. The counts on this page do not include these reports.
FDA received 110 reports in the 12 months to June 2026 and 111 in the 12 months before. FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.
Of the 1,332,454 drug reports that FDA received in the 12 months to June 2026, 110 (under 0.1%) name Letermovir. Reports from consumers or other non-health professionals were 7.6% of the reports that name Letermovir and 45.8% of all drug reports.
The number of people who use the product is not in the data. A count is not a rate. A count of reports is not a count of events or of patients, because one event can have more than one report.
There are many instances of duplicative reports and some reports do not contain all the necessary information.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
Suspect product
FDA records each drug in a report as suspect, concomitant or interacting. This page counts the reports in which Letermovir is suspect or interacting. FDA says:
Any number of the drugs may be marked as suspect if thought to be responsible for one or more of the reactions, but that information is not validated.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
Data version
openFDA FAERS release of 29 Oct 2026. Reports received through 30 Jun 2026.
Since the last update
FDA says:
Many factors can influence whether or not an event will be reported, such as the time a product has been marketed and publicity about an event.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The information in these reports cannot be used to estimate the incidence (occurrence rates) of the events reported.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
The latest update of the FDA data, recorded on , changed no count of this page.
- In April to June 2026, FDA received 21 reports that name Letermovir.
- In January to March 2026, FDA received 21.
- In April to June 2025, FDA received 53.
April to June 2026 is the latest closed quarter in the data. A closed quarter is a quarter for which the FDA files have most of the reports.
Reaction lookup
These are the reaction terms that the reports record, with the number of reports for each term. Type a term or a plain word to find its count.
What this list leaves out
The table lists the 62 reaction terms that 5 or more reports record. A term with fewer than 5 reports is not in the table.
The site keeps reaction terms for 558 of the 565 reports (98.8%).
The reports of the other years are not in the counts.
So a count in the table can be lower than the count of FDA.
The table shows the first 50 of 62 terms.
| Reaction term (MedDRA) and plain meaning | Reports | Share of the 565 reports |
|---|---|---|
| Off label useused for a purpose or in a way not on the label | 126 | 22.3% |
| Drug interactionan interaction between medicines | 100 | 17.7% |
| Drug ineffectivethe medicine did not work as expected | 58 | 10.3% |
| Cytomegalovirus infection reactivation | 49 | 8.7% |
| Product use in unapproved indicationused for a purpose not on the label | 43 | 7.6% |
| Neutropenialow neutrophils, a type of white blood cell | 40 | 7.1% |
| Pathogen resistance | 39 | 6.9% |
| Cytomegalovirus viraemia | 38 | 6.7% |
| Drug resistance | 37 | 6.5% |
| Acute kidney injurysudden loss of kidney function | 34 | 6% |
| Cytomegalovirus infection | 34 | 6% |
| Drug level increaseda raised blood level of the medicine | 31 | 5.5% |
| Septic shockshock arising from infection | 31 | 5.5% |
| Post transplant lymphoproliferative disorder | 30 | 5.3% |
| Thrombotic microangiopathy | 21 | 3.7% |
| Leukopenialow white blood cells | 20 | 3.5% |
| Acute graft versus host disease in skin | 18 | 3.2% |
| Cytomegalovirus test positive | 17 | 3% |
| Treatment failurethe treatment did not work | 17 | 3% |
| Diarrhoealoose or frequent stools | 16 | 2.8% |
| Hepatic failureliver failure | 16 | 2.8% |
| Immunosuppressant drug level increased | 16 | 2.8% |
| Covid-19COVID-19 infection | 15 | 2.7% |
| Cytomegalovirus colitis | 13 | 2.3% |
| Pancytopenialow counts of all blood cells | 13 | 2.3% |
| Aspergillus infection | 12 | 2.1% |
| Altered state of consciousness | 11 | 1.9% |
| Deaththe patient died; cause not stated by this term | 11 | 1.9% |
| Viral load increased | 11 | 1.9% |
| Atrial fibrillationan irregular heart rhythm | 10 | 1.8% |
| Cardiac failure acute | 9 | 1.6% |
| Lichenoid keratosis | 9 | 1.6% |
| Pyrexiafever | 9 | 1.6% |
| Brain abscess | 8 | 1.4% |
| Condition aggravatedthe condition being treated got worse | 8 | 1.4% |
| Dyspnoeashortness of breath | 8 | 1.4% |
| Epstein-Barr virus infection reactivation | 8 | 1.4% |
| Guillain-Barre syndromea nerve disorder causing weakness | 8 | 1.4% |
| Product administration errora mistake in giving the product | 8 | 1.4% |
| Renal failurekidney failure | 8 | 1.4% |
| Sepsisa severe body-wide response to infection | 8 | 1.4% |
| Acute graft versus host disease | 7 | 1.2% |
| Anaemialow red blood cells | 7 | 1.2% |
| Febrile neutropeniafever with low white blood cells | 7 | 1.2% |
| Hypoglycaemialow blood sugar | 7 | 1.2% |
| Incorrect dose administeredthe wrong dose was given | 7 | 1.2% |
| Lactic acidosisa build-up of lactic acid in the blood | 7 | 1.2% |
| Toxicity to various agentspoisoning or toxic effect of one or more substances | 7 | 1.2% |
| Acute myeloid leukaemia | 6 | 1.1% |
| Adverse eventan unwanted medical event, type not specified | 6 | 1.1% |
The counts add to more than 565 reports, because one report can record more than one term. FDA says:
No individual drug is connected to any individual reaction. When a report lists multiple drugs and multiple reactions, there is no way to conclude from the data therein that a given drug is responsible for a given reaction.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The CSV file has the same rows and the same limits. Its last row is a note that says so.
MedDRA term
The person who codes a report selects the preferred term that agrees best with the description of the reporter. The words under a term are the plain meaning that this site gives.
Not the label
The FDA-approved label of a product lists its adverse reactions. See the official pages at the end of this page.
Same ingredient, other names
Reporters write a brand name or a generic name. Each name has its own page and its own count.
| Name | Name type | Reports |
|---|---|---|
| Letermovir (this page) | Generic name | 565 |
| Prevymis | Brand name | 1,063 |
Sum of the separately reported names: 1,628. A report that names two of these names is in the sum two times. The sum is not the number of reports for the ingredient.
FDA says:
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.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
Importantly, the AEMS data by themselves are not an indicator of the safety profile of the drug or biologic.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
Outcomes by year
The table gives the outcomes that the reporters gave, in the terms of FDA.
Outcomes in the reports that name Letermovir, by the year of the openFDA file that holds the report
The table continues to the right.
| Year of the openFDA file | Reports | Serious | Death | Life-threatening | Hospitalization (initial or prolonged) | Disability or Permanent Damage | Congenital Anomaly/Birth Defect | Other Serious (Important Medical Events) | Not serious |
|---|---|---|---|---|---|---|---|---|---|
| 2018 | 7 | 6 | 4 | 1 | 1 | 0 | 0 | 6 | 1 |
| 2019 | 21 | 21 | 3 | 5 | 2 | 1 | 0 | 17 | 0 |
| 2020 | 49 | 46 | 10 | 2 | 5 | 0 | 0 | 44 | 3 |
| 2021 | 75 | 74 | 14 | 4 | 35 | 0 | 0 | 65 | 1 |
| 2022 | 71 | 71 | 10 | 0 | 27 | 0 | 0 | 60 | 0 |
| 2023 | 73 | 72 | 12 | 9 | 28 | 1 | 0 | 61 | 1 |
| 2024 | 82 | 82 | 24 | 4 | 27 | 0 | 0 | 74 | 0 |
| 2025 | 143 | 104 | 13 | 8 | 25 | 0 | 0 | 88 | 39 |
| 2026 | 44 | 38 | 9 | 2 | 3 | 0 | 0 | 31 | 6 |
An outcome in a report is not proof that the drug was the cause. The reporter gives the outcome, and FDA does not verify it. FDA says:
The information in these reports has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
The six headings with the names of FDA are the outcome terms of FDA. A report can have more than one outcome. The columns Serious and Not serious are the two values of the openFDA field serious. For the value serious, openFDA gives this description:
The adverse event resulted in death, a life threatening condition, hospitalization, disability, congenital anomaly, or other serious condition
Source: openFDA, Drug adverse event fields (YAML reference). The site read the page on .
The year is the year of the openFDA file that holds the latest version of the report. It is not always the year in which FDA first received the report. The chart of the next section uses the year of first receipt. The latest year is not complete.
Reports by year and month
The column of 2026 has an outline, because the year is not complete. It has the reports that FDA received through June 2026 only.
Show the figures of the chart as a table
| Year | Reports |
|---|---|
| 2018 | 16 |
| 2019 | 33 |
| 2020 | 43 |
| 2021 | 79 |
| 2022 | 70 |
| 2023 | 69 |
| 2024 | 78 |
| 2025 | 135 |
| 2026 | 42 |
FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.
Why a count moves
A count moves for many reasons. The guide gives FDA's words about them.
Patients and reporters
| Age | Reports | Share | Share as a bar |
|---|---|---|---|
| Under 2 | 5 | 0.9% | |
| 2 to 11 | 26 | 4.6% | |
| 12 to 17 | 20 | 3.5% | |
| 18 to 44 | 126 | 22.3% | |
| 45 to 64 | 212 | 37.5% | |
| 65 to 74 | 48 | 8.5% | |
| 75 and over | 3 | 0.5% | |
| Age not given | 125 | 22.1% |
| Sex | Reports | Share | Share as a bar |
|---|---|---|---|
| Female | 194 | 34.3% | |
| Male | 259 | 45.8% | |
| Unknown or not given | 112 | 19.8% |
| Reporter | Reports | Share | Share as a bar |
|---|---|---|---|
| Physician | 222 | 39.3% | |
| Pharmacist | 21 | 3.7% | |
| Other health professional | 275 | 48.7% | |
| Lawyer | 0 | 0% | |
| Consumer or non-health professional | 43 | 7.6% | |
| Not given | 4 | 0.7% |
Age and sex are as the report gives them. The reporter is the primary source in the report. 24.4% of the reports give the United States as the country.
Reason for use
| Indication as recorded (MedDRA) | Reports | Share |
|---|---|---|
| Antiviral prophylaxis | 268 | 47.4% |
| Cytomegalovirus infection | 54 | 9.6% |
| Prophylaxis | 50 | 8.8% |
| Cytomegalovirus viraemia | 27 | 4.8% |
| Bone marrow transplant | 10 | 1.8% |
| Cytomegalovirus colitis | 7 | 1.2% |
The reporter fills in the indication, and the field is often empty. Each share is of all 565 reports.
Drugs in the same reports
| Drug | Reports that name the two |
|---|---|
| Acyclovir | 68 |
| Cyclophosphamide | 68 |
| Cyclosporine | 109 |
| Foscarnet | 54 |
| Ganciclovir | 88 |
| Methylprednisolone | 44 |
| Mycophenolate mofetil | 93 |
| Prednisone | 58 |
| Tacrolimus | 147 |
| Valganciclovir | 93 |
The table has the 10 drug names that these reports name most. Two names in one report says only that the report recorded the two. It says nothing about the part of a product in the event.
FDA says:
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.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
Importantly, the AEMS data by themselves are not an indicator of the safety profile of the drug or biologic.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
Pages near this one
- Prevymis same ingredient
- Letairis next in the A to Z list
- Letrozol next in the A to Z list
- Lescol next in the A to Z list
- Letrozole next in the A to Z list
- Lergigan Promethazine Hydrochloride next in the A to Z list
- Letybo next in the A to Z list
- Lergigan next in the A to Z list
- Leucovorin next in the A to Z list
- Lercanidipine hydrochloride next in the A to Z list
- Leucovorin calcium next in the A to Z list
- Lercanidipine next in the A to Z list
These links are for navigation. No count selected them.
Official pages
- DailyMed labels for LetermovirThe labels (prescribing information) that have this name, at the National Library of Medicine.
- MedWatch Online Voluntary Reporting FormThe online form of FDA for a voluntary report.
- MedWatch: The FDA Safety Information and Adverse Event Reporting ProgramThe page of the FDA program that receives reports about drugs and devices.
- FDA Adverse Event Monitoring System (AEMS) Public DashboardThe public dashboard of FDA for adverse event reports on drugs and biologics.
The site checked these addresses on . The links open in a new tab.
Cite this page
Reported Reactions. Letermovir: adverse event reports that FDA received. https://reportedreactions.com/drug/letermovir/ Source: U.S. Food and Drug Administration, openFDA Drug Adverse Event (FAERS) files, release of . Reports received through .
Where the data come from
The counts come from the openFDA Drug Adverse Event (FAERS) bulk files, release of 29 Oct 2026. The files have the reports that FDA received through 30 Jun 2026. A drug name is the name on the report. The site matches it to a brand name or a generic name of the National Drug Code Directory of 2 Nov 2026. A class is the pharmacologic class (EPC) of the FDA label.
A report is in the count when it names Letermovir as a suspect or interacting product. The 899 reports that name it only as a concomitant medicine are not in the count. The site does not publish a report narrative, a lot number, a detail of a patient or the identity of a reporter. The record of FDA is the authority. See how the site counts reports, the data sources and the corrections page.
Questions
Do these reports show that Letermovir was responsible for the reactions?
No. FDA says:
For any given report, there is no certainty that a suspected drug caused the event.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of . The site read the page on .
A reaction can relate to the condition that the drug treats, to other medicines, or to something else.
Is this the list of reactions on the label of Letermovir?
No. It is a count of what people reported to FDA: 565 reports from May 2018 to June 2026. The FDA-approved label of a product lists its adverse reactions. The official pages at the end of this page link to the labels.
Who sent these reports?
Other health professional (48.7%), physician (39.3%) and consumer or non-health professional (7.6%). These are the types of reporter for the reports that name this drug.
If a manufacturer receives an adverse event report, it is normally required to send the report to FDA.
Source: openFDA, Drug Adverse Event Overview. The site read the page on .
How does a person report an adverse event?
FDA runs MedWatch, a program that takes voluntary reports from health professionals, patients and consumers. The guide on how to report has the links.