Rituximab Does Not Cause Sinusoidal Obstruction Syndrome
Based on the highest quality guideline evidence and FDA labeling, rituximab is not recognized as a cause of sinusoidal obstruction syndrome (SOS). The 2016 EASL Clinical Practice Guidelines provide a comprehensive list of major causes of SOS, and rituximab is notably absent 1. The FDA label for rituximab does not list SOS as a known adverse effect 2.
Evidence from Guidelines
The EASL guidelines explicitly enumerate drugs associated with SOS, including:
- Chemotherapeutic agents: Actinomycin D, busulfan, carmustine, cyclophosphamide, dacarbazine, melphalan, mercaptopurine, mitomycin, oxaliplatin, cytosine arabinoside
- Antibody-drug conjugates: Gemtuzumab ozogamicin and inotuzumab ozogamicin (notably, these are CD33 and CD22-targeted agents, not CD20-targeted like rituximab)
- Immunosuppressants: Azathioprine, 6-mercaptopurine, 6-thioguanine
- Other agents: Pyrrolizidine alkaloids, urethane, terbinafine 1
Mechanism and Risk Context
SOS results from sinusoidal endothelial cell injury, leading to denudation, cell sloughing, and subsequent sinusoidal obstruction 1. The condition is most commonly associated with:
- Myeloablative conditioning regimens for hematopoietic stem cell transplantation
- Specific chemotherapeutic agents with direct endothelial toxicity
- Antibody-drug conjugates containing calicheamicin (gemtuzumab ozogamicin, inotuzumab ozogamicin) 3, 4, 5
Rituximab, as a naked monoclonal antibody targeting CD20, lacks the direct endothelial toxicity mechanism that characterizes SOS-inducing agents. The FDA label details extensive adverse effects of rituximab including infusion reactions, infections, cardiac events, tumor lysis syndrome, and renal toxicity, but makes no mention of SOS or hepatic veno-occlusive disease 2.
Recent Pharmacovigilance Data
A 2025 real-world pharmacovigilance study analyzing the FDA Adverse Event Reporting System (FAERS) from 2004-2022 identified the top 50 medications associated with SOS 6. Rituximab was not among these medications, further supporting that it is not a recognized cause of SOS. The drugs with strongest associations were tioguanine, inotuzumab ozogamicin, gemtuzumab ozogamicin, busulfan, and dactinomycin 6.
Clinical Implications
If a patient receiving rituximab develops signs suggestive of SOS (weight gain, hepatomegaly, jaundice, ascites), alternative etiologies must be investigated:
- Concomitant hepatotoxic chemotherapy agents
- Prior or concurrent antibody-drug conjugates
- Conditioning regimens for transplantation
- Other causes of hepatic dysfunction (viral hepatitis, drug-induced liver injury from other agents, hepatic vein thrombosis)
The 2021 AASLD guidance emphasizes the importance of distinguishing SOS from other vascular liver disorders through appropriate diagnostic evaluation including imaging and, when indicated, transjugular liver biopsy with hepatic venous pressure gradient measurement 7.
In summary, rituximab should not be considered a causative agent for SOS based on current guideline evidence, FDA labeling, and pharmacovigilance data.