Can Rituximab Cause Diarrhea? A Comprehensive Guide

October 12, 2025 •

4 min read

Studies have shown that in some patient populations, such as those with granulomatosis with polyangiitis (GPA), diarrhea can affect around 17% of individuals treated with rituximab. As a recognized but potentially concerning side effect, it is important for patients and caregivers to understand if can rituximab cause diarrhea, what the underlying causes might be, and when to seek medical attention.

Quick Summary

Diarrhea is a known side effect of rituximab treatment. The severity can vary, and in some cases, it may signal a more serious underlying condition such as tumor lysis syndrome or colitis.

Key Points

Yes, rituximab can cause diarrhea: Diarrhea is a recognized and relatively common side effect of rituximab treatment.
Incidence varies by condition: Studies have shown varying rates of diarrhea, with some indicating it occurs in 10-17% of patients, depending on the treated condition.
Diarrhea can be a sign of colitis: In some cases, rituximab can cause colitis (inflammation of the colon), which can manifest as delayed-onset diarrhea and abdominal pain.
Watch for signs of Tumor Lysis Syndrome: Diarrhea, nausea, and vomiting can be symptoms of Tumor Lysis Syndrome (TLS), a serious condition that can occur within 12-24 hours of an infusion.
Risk may be higher with chemotherapy: When rituximab is combined with other chemotherapy agents, the risk of serious gastrointestinal complications, including bowel obstruction or perforation, may increase.
Mild diarrhea can be managed with supportive care: For uncomplicated cases, treatment involves proper hydration, dietary changes, and, with a doctor's approval, antimotility agents.
Serious symptoms require immediate medical attention: Any severe or persistent diarrhea, along with other symptoms like fever, blood in stool, or intense abdominal pain, should be reported to a healthcare provider promptly.

Understanding Rituximab: Mechanism and Purpose

Rituximab is a monoclonal antibody that targets the CD20 antigen found on the surface of B-cells. It is widely used to treat various conditions, including certain types of non-Hodgkin's lymphoma, chronic lymphocytic leukemia, rheumatoid arthritis, and other autoimmune diseases. The medication works by binding to B-cells and initiating their destruction, which helps reduce the number of abnormal B-cells in cancer or suppresses the immune response in autoimmune disorders. While highly effective, this targeted approach can also lead to a range of side effects, including gastrointestinal issues like diarrhea.

Can rituximab cause diarrhea? The answer is yes.

Diarrhea is a reported adverse event associated with rituximab use. The incidence can vary depending on the patient population and the condition being treated, but it is considered a common side effect. In clinical trials for GPA and microscopic polyangiitis (MPA), diarrhea was observed in 17% of rituximab-treated patients. In other studies, the rate has been reported as 10%. While often mild, it can sometimes be a symptom of a more serious underlying complication.

Potential Causes of Rituximab-Induced Diarrhea

The mechanisms behind rituximab-associated diarrhea are not fully understood, but there are several potential causes ranging from mild gastrointestinal upset to more severe conditions.

Rituximab-Associated Colitis

One potential cause is rituximab-associated colitis (RC), a form of inflammation in the colon. A retrospective study of cancer patients found that 4% developed RC following rituximab treatment. The median time to onset was 181 days, suggesting it is a delayed side effect rather than an immediate infusion reaction. While typically mild and manageable with supportive care, RC can, in rare instances, lead to severe complications like colonic perforation.

Tumor Lysis Syndrome (TLS)

Diarrhea can also be an early sign of a rare but life-threatening complication called tumor lysis syndrome (TLS). TLS occurs when large numbers of cancer cells are rapidly broken down and their contents are released into the bloodstream. This can lead to a dangerous imbalance of electrolytes and can happen within 12 to 24 hours of an infusion. Patients receiving rituximab for non-Hodgkin's lymphoma are particularly at risk for this complication. Other symptoms of TLS include nausea, vomiting, muscle cramps, and fatigue.

Concomitant Therapies

The risk and severity of diarrhea may also be influenced by other medications taken with rituximab. When used with chemotherapy drugs, the risk of serious stomach and bowel problems, including obstruction or tears in the bowel, is increased. Always inform your healthcare provider about all medications you are taking to help assess your overall risk.

Managing Diarrhea Associated with Rituximab

If you experience diarrhea while on rituximab, a healthcare provider will first evaluate the potential underlying cause, especially if it is severe or accompanied by other symptoms. The management approach depends on the severity and cause.

For mild to moderate diarrhea, the following steps are generally recommended:

Hydration: Drinking plenty of fluids, such as water and electrolyte-containing sports drinks, is crucial to prevent dehydration.
Dietary modifications: Eating bland, easy-to-digest foods can help. The BRAT diet (bananas, rice, applesauce, toast) is often recommended.
Antimotility agents: Over-the-counter medications like loperamide (Imodium) may be used, but only after consulting a healthcare provider.

When to Contact a Healthcare Provider Immediately:

Severe or persistent diarrhea: If diarrhea does not improve or worsens.
Blood in the stool: A sign of potential colitis or gastrointestinal bleeding.
Severe abdominal pain, constipation, or vomiting: These may indicate more serious bowel issues.
Signs of infection: Such as fever and chills.
Signs of dehydration: Including dizziness, decreased urination, or unusual fatigue.

Comparison Table: Causes and Characteristics of Diarrhea with Rituximab


Feature	Mild Gastrointestinal Upset	Rituximab-Associated Colitis (RC)	Tumor Lysis Syndrome (TLS)
Timing of Onset	Can occur during or after infusion.	Delayed onset, median of 181 days.	Within 12-24 hours of first infusion.
Associated Symptoms	Nausea, vomiting, stomach upset.	Abdominal pain, blood per rectum, fever.	Nausea, vomiting, muscle cramps, fatigue.
Severity	Usually mild and self-limiting.	Typically mild, but can be severe in rare cases.	Potentially life-threatening.
Underlying Mechanism	Not fully elucidated; possible direct effect.	Inflammation of the colon, related to immune response.	Rapid breakdown of cancer cells.
Management	Supportive care (hydration, diet), possibly antimotility agents.	Supportive care, potentially immunosuppressants in severe cases.	Immediate aggressive intravenous hydration and medication.

Conclusion: Prioritizing Communication and Care

In summary, diarrhea is a known side effect of rituximab and can arise from various causes, including mild gastrointestinal upset, colitis, or more seriously, tumor lysis syndrome. While it is often manageable with simple supportive care, patients must remain vigilant for any signs of worsening symptoms or potential complications. Clear and open communication with your healthcare team is paramount. By reporting any new or concerning symptoms promptly, patients and providers can work together to ensure the safe and effective use of rituximab.

For more information on the mechanisms and use of rituximab, you can visit the National Institutes of Health (NIH) website: https://www.ncbi.nlm.nih.gov/books/NBK564374/.

Frequently Asked Questions

Yes, diarrhea is a relatively common side effect of rituximab. Clinical trial data shows that the incidence can range from approximately 10% to 17% in different patient populations and treatment contexts.

For mild diarrhea, focus on staying hydrated by drinking plenty of fluids. Consider eating bland foods like bananas, rice, applesauce, and toast. Always inform your doctor or healthcare team so they can assess the situation and rule out more serious causes.

Yes, diarrhea can be a symptom of a serious side effect. It could be an indicator of Tumor Lysis Syndrome (TLS) in cancer patients, or in rare cases, rituximab-associated colitis.

The timing can vary. Diarrhea can occur relatively soon after an infusion as a general gastrointestinal upset. However, if it is caused by rituximab-associated colitis, it may have a delayed onset, sometimes months after starting treatment.

Rituximab-associated colitis (RC) is an inflammation of the colon that has been linked to rituximab therapy. Diarrhea, sometimes accompanied by abdominal pain and blood in the stool, is a primary symptom of RC. While often mild, a colonoscopy may be needed for diagnosis in some cases.

You should contact your doctor immediately if you experience severe or persistent diarrhea, blood in your stool, severe abdominal pain, fever, or any signs of dehydration such as dizziness or decreased urination.

For mild diarrhea, a doctor might recommend an over-the-counter medication like loperamide. However, it is crucial to consult your healthcare provider first, as taking antidiarrheal medication without proper evaluation could mask a more serious condition.