Risk of Thrombosis in PNH Controlled on Ravulizumab
Patients with PNH controlled on ravulizumab maintain a significantly reduced but not eliminated risk of thrombosis, with an incidence of approximately 1.5 per 100 patient-years, compared to the 40-67% mortality from thrombotic events in untreated PNH. 1, 2
Baseline Thrombotic Risk in PNH
PNH carries an inherently high thrombotic burden. Untreated PNH patients face thrombotic events in up to 40% of cases, with thrombosis accounting for 40-67% of deaths 3, 2. The disease is particularly associated with unusual site venous thrombosis, including splanchnic vessels (Budd-Chiari syndrome in 9-19% of tested patients), portal veins, and cerebral veins 4, 5.
Impact of Ravulizumab on Thrombotic Risk
Ravulizumab, a long-acting C5 inhibitor, provides immediate, complete, and sustained complement inhibition over 8-week dosing intervals 1. The drug achieves:
- Complete C5 inhibition (free C5 <0.5 mcg/mL) by the end of the first infusion, sustained throughout treatment 1
- Reduced breakthrough hemolysis compared to eculizumab (4.0% vs 10.7% in complement inhibitor-naïve patients; 0% vs 5.1% in eculizumab-stabilized patients) 6
- Sustained terminal complement blockade that eliminates thrombotic events associated with suboptimal C5 inhibition 6
Residual Thrombotic Risk on Treatment
Despite effective complement inhibition, thrombotic events still occur in ravulizumab-treated patients at approximately 1.5 per 100 patient-years 2. Key risk factors for thrombosis during treatment include:
High-Risk Features:
- Prior thrombotic history: Patients with pre-treatment thrombosis have significantly higher rates of recurrent events during treatment (p=0.014) 2
- Elevated LDH levels: 61.5% of patients experiencing thrombotic events had LDH >1.5× upper limit of normal within the week before onset, indicating inadequate intravascular hemolysis control 2
- Concurrent infections: Associated with increased thrombotic events 2
- Extended dosing intervals: Longer intervals between doses correlate with higher thrombotic risk 2
- PNH clone size >60%: Historically associated with greater thrombotic risk 4
Common Thrombotic Sites on Treatment:
Most frequent events remain deep vein thrombosis and cerebral infarction (14.8% each) 2
Anticoagulation Strategy
Concurrent anticoagulation with ravulizumab is clinically useful and should be strongly considered, particularly in patients with prior thrombotic history 2. The evidence shows:
- 71.8% of thrombotic events occurred during anticoagulant off-periods versus 28.2% during on-periods 2
- Warfarin and low-molecular-weight heparin are established options; direct oral anticoagulants may be considered in selected cases 3
- Anticoagulation should be used in combination with C5 inhibitors, not as monotherapy 3
Monitoring and Prevention
Essential Monitoring Parameters:
- LDH levels: Rising LDH suggests inadequate complement control and increased thrombotic risk 2
- Infection surveillance: Prompt treatment of infections to minimize thrombotic triggers 2
- Dosing adherence: Ensure 8-week intervals are maintained; avoid extended intervals 2
- Free C5 levels: Should remain <0.5 mcg/mL for optimal protection 1
Specific Prophylaxis Recommendations:
For patients with prior thrombotic history, indefinite anticoagulation concurrent with ravulizumab is warranted given the significantly elevated recurrence risk 2. For patients without prior thrombosis, individualized assessment should weigh:
- PNH clone size
- LDH control
- Presence of additional prothrombotic risk factors (hormonal therapy, myeloproliferative features, JAK2V617F mutation) 7, 5
Critical Pitfalls
Do not discontinue anticoagulation solely because complement inhibition is achieved—the residual thrombotic risk persists, particularly in high-risk patients 2. Rising LDH during treatment signals inadequate disease control and warrants immediate evaluation for breakthrough hemolysis and consideration of dose adjustment or alternative complement inhibitors 2. Infections require aggressive management as they independently increase thrombotic risk even with adequate complement blockade 2.