What the label lists and what reports show
Bezlotoxumab side effects
Bezlotoxumab's FDA label: “The most common adverse reactions (reported in ≥4% of adult patients) included nausea, pyrexia, and headache.” FAERS holds 349 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 (128 reports).
- No generic listed
Check it at the source: the bezlotoxumab FDA label on DailyMed (effective November 12, 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 ZINPLAVA?ZINPLAVA may cause serious side effects, including: Heart failure. Heart failure may happen in people who receive ZINPLAVA and can be serious. People with a history of congestive heart failure (CHF) who received ZINPLAVA had a higher rate of heart failure and death than those who did not receive ZINPLAVA. Common side effects of ZINPLAVA: The most common side effects that may happen on the day of or the day after receiving ZINPLAVA include: nausea headache fever feeling tired shortness of breath feeling dizzy high blood pressure The most common side effects that may happen up to four weeks after receiving ZINPLAVA include: nausea fever headache If you have any side effect that bothers you or does not go away, tell your doctor. These are not all the possible side effects of ZINPLAVA. For more information, ask your doctor or pharmacist. Call your doctor for medical advice about side effects. […]
Source: FDA drug label, Merck Sharp & Dohme LLC, effective November 12, 2024 (SPL set 8f479bfe-2bfa-4cc5-9aee-1357364480b0), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (reported in ≥4% of adult patients) included nausea, pyrexia, and headache.
From the label: adverse reactions, continuedAdult Patients: The most common adverse reactions (reported in ≥4% of adult patients) included nausea, pyrexia, and headache. ( 6.1 ) Pediatric Patients: The most common adverse reactions (reported in >10% of pediatric patients) were pyrexia and headache ( 6.1 ) 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. Clinical Trials Experience in Adults The safety of ZINPLAVA was evaluated in two placebo-controlled Phase 3 trials (Trial 1 n=390 and Trial 2 n=396). Patients received a single 10 mg/kg intravenous infusion of ZINPLAVA and concomitant standard of care (SoC) antibacterial drugs (metronidazole, vancomycin or fidaxomicin) for CDI. Adverse reactions reported within the first 4 weeks after ZINPLAVA was administered are described for the pooled Phase 3 trial population of 786 patients. The median age of patients receiving ZINPLAVA was 65 years (range 18 to 100), 50% were age 65 years or older, 56% were female, and 83% were white. …
Source: FDA drug label, Merck Sharp & Dohme LLC, effective November 12, 2024 (SPL set 8f479bfe-2bfa-4cc5-9aee-1357364480b0), via openFDA; the full label on DailyMed
What do FAERS reports show?
349 reports list bezlotoxumab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 63 are coded as a death and 109 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 20 reactions below, 3 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.
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?
- Bezlotoxumab: 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