Bezlotoxumab is an intravenous human monoclonal antibody against Clostridioides difficile toxin B used as a one-time adjunct to standard antibiotics to reduce recurrent CDI in high‑risk adults.
Bezlotoxumab is a fully human IgG1 monoclonal antibody that binds C. difficile toxin B but not toxin A.
It is indicated as a single IV dose, given during standard-of-care CDI antibiotics, to prevent recurrence in adults at increased risk (age ≥65, immunocompromised, severe CDI, or prior rCDI).
Bezlotoxumab binds specific epitopes in the TcdB CROP domain, blocking the toxin’s carbohydrate-binding pockets and preventing attachment to colonic epithelial cells.
Given intravenously, the antibody reaches the inflamed colonic mucosa, crosses into the lumen, neutralizes toxin B locally, and thereby reduces toxin-mediated inflammation without affecting the organism or microbiota directly.
Recommended dose: 10 mg/kg IV once, infused over about 60 minutes, during a standard course of CDI antibiotics (e.g., vancomycin, fidaxomicin).
Bezlotoxumab has a terminal half‑life of roughly 19 days, so no repeat dosing is typically required in a given treatment course.
## Efficacy data (MODIFY I/II)
In the phase 3 MODIFY I and II trials this agent added to SOC antibiotics reduced 12‑week recurrent CDI vs placebo: 17% vs 28% in MODIFY I and 16% vs 26% in MODIFY II.
The pooled sustained cure at 12 weeks) was 64% with bezlotoxumab vs 54% with placebo, with greater absolute benefit in predefined high‑risk subgroups (older age, prior rCDI, immunocompromise, severe CDI).
Common adverse reactions include nausea, pyrexia, and headache; infusion‑related reactions (nausea, dizziness, dyspnea, hypertension, fatigue) occurred in about 10% vs 8% with placebo, generally mild.
Serious adverse events overall were similar to placebo, but heart failure events were numerically higher with bezlotoxumab (≈2.3% vs 1.0%), so caution is advised in patients with a history of congestive heart failure.