What the label lists and what reports show
Fidaxomicin side effects
Fidaxomicin's FDA label: “The most common adverse reactions in adults (incidence ≥2%) are nausea, vomiting, abdominal pain, gastrointestinal hemorrhage, anemia, and neutropenia.” FAERS holds 2,385 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is clostridium difficile infection (480 reports).
- Generic listed
Check it at the source: the fidaxomicin FDA label on DailyMed (effective October 16, 2024, Merck Sharp & Dohme LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of DIFICID?DIFICID can cause serious side effects, including: Allergic reaction. If you get a severe allergic reaction while taking DIFICID, including problems breathing or shortness of breath, rash, itching or hives, or swelling of the mouth, throat, or face, stop taking DIFICID and get emergency medical help right away. […]
Source: FDA drug label, NDA201699 (Cubist Pharms Llc), as published by Merck Sharp & Dohme LLC, effective October 16, 2024 (SPL set dd966338-c820-4270-b704-09ef75fa3ceb), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions in adults (incidence ≥2%) are nausea, vomiting, abdominal pain, gastrointestinal hemorrhage, anemia, and neutropenia.
Table 3: Selected Adverse Reactions with an Incidence of ≥5% Reported in DIFICID-Treated Pediatric Patients in the Controlled Trial
| System Organ Class Adverse Reaction | DIFICID (N=98) n (%) | Vancomycin (N=44) n (%) |
|---|---|---|
| Abdominal pain Includes abdominal pain, abdominal pain lower, and abdominal pain upper | 8 (8.2) | 9 (20.5) |
| Vomiting | 7 (7.1) | 6 (13.6) |
| Diarrhea | 7 (7.1) | 5 (11.4) |
| Constipation | 5 (5.1) | 1 (2.3) |
| Pyrexia | 13 (13.3) | 10 (22.7) |
| Aminotransferases increased Includes alanine aminotransferase increased, aspartate… | 5 (5.1) | 1 (2.3) |
| Rash Includes rash, rash follicular, rash maculo-papular, and exfoliative rash | 5 (5.1) | 1 (2.3) |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe most common adverse reactions in adults (incidence ≥2%) are nausea, vomiting, abdominal pain, gastrointestinal hemorrhage, anemia, and neutropenia. ( 6 ) The most common adverse reactions in pediatric patients (incidence ≥5%) treated with DIFICID are pyrexia, abdominal pain, vomiting, diarrhea, constipation, increased aminotransferases, and rash. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Merck Sharp & Dohme LLC at 1-877-888-4231 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Adults The safety of DIFICID 200 mg tablets taken twice a day for 10 days was evaluated in 564 adult patients with CDAD in two active-controlled trials with 86.7% of patients receiving a full course of treatment. Thirty-three adult patients receiving DIFICID (5.9%) withdrew from trials as a result of adverse reactions (AR). The types of AR resulting in withdrawal from the study varied considerably. Vomiting was the primary adverse reaction leading to discontinuation of dosing; this occurred at an incidence of 0.5% in both the DIFICID and vancomycin patients in Phase 3 trials. …
Source: FDA drug label, NDA201699 (Cubist Pharms Llc), as published by Merck Sharp & Dohme LLC, effective October 16, 2024 (SPL set dd966338-c820-4270-b704-09ef75fa3ceb), via openFDA; the full label on DailyMed
What do FAERS reports show?
2,385 reports list fidaxomicin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 257 are coded as a death and 747 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 17 reactions below, 8 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Fidaxomicin: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions