Most Common Adverse Event with Caplacizumab
The most common adverse event associated with caplacizumab is bleeding, particularly mild to moderate mucocutaneous bleeding including epistaxis (nosebleeds), gingival bleeding, and gastrointestinal bleeding. 1
Bleeding Risk Profile
The bleeding complications are directly related to caplacizumab's mechanism of action—it disrupts von Willebrand factor (VWF) and platelet interaction, which is precisely how it treats iTTP but also creates a predictable bleeding risk 1.
Specific Bleeding Events by Frequency:
- Mucocutaneous bleeding occurred in 65% of patients receiving caplacizumab versus 48% in placebo groups 2
- Epistaxis (nosebleeds) - most frequently reported 1, 3
- Gingival bleeding - common 1, 3
- Gastrointestinal bleeding - moderately common 1, 3
- Heavy menstrual bleeding and vaginal hemorrhage - documented in female patients 3
Severity Considerations:
Most bleeding episodes are mild to moderately severe 1. However, severe bleeding such as intracranial hemorrhage can occur, making caplacizumab contraindicated in patients with risk of or presenting with hemorrhagic stroke 1.
Timing of Adverse Events
Bleeding events tend to occur early during therapy. Analysis of 401 reports showed 40.4% of adverse events occurred within 7 days of administration 3. Weibull modeling from FAERS data demonstrated an "early-failure pattern," indicating greater susceptibility during initial treatment cycles 4.
Other Notable Adverse Events
Beyond bleeding, real-world pharmacovigilance identified additional safety signals 3:
- Injection site reactions (pain, bruising, erythema, hemorrhage)
- Contusion
- Pruritus and rash
The overall adverse event rate in caplacizumab-treated patients was 36% (pooled estimate 0.36,95% CI 0.16-0.60), with serious adverse events at 8% 1.
Clinical Management Implications
Close monitoring is essential during the initial treatment period, particularly for:
- Hematologic parameters
- Signs of bleeding (especially mucosal sites)
- Injection site assessment
If severe bleeding occurs, it can be controlled by administering VWF concentrate 5.
The bleeding risk must be balanced against caplacizumab's remarkable mortality reduction (from historical rates to <5%) and rapid platelet recovery 1. The predictable nature of these bleeding events allows for proactive monitoring strategies rather than treatment avoidance in appropriate candidates.