Does Rituxan cause diarrhea? Understanding Rituximab's Gastrointestinal Effects

October 8, 2025 •

4 min read

According to clinical data, diarrhea occurred in 10-17% of patients taking Rituxan for certain conditions like GPA, MPA, or NHL, confirming that Does Rituxan cause diarrhea? is a question with a clear affirmative answer. This side effect can manifest in various ways, from common gastrointestinal upset to more serious, albeit rarer, complications.

Quick Summary

Rituxan can indeed cause diarrhea, a reported side effect that ranges from mild stomach upset to an indicator of more severe conditions. Management depends on the cause and severity. Timely communication with your healthcare provider is crucial.

Key Points

Common Side Effect: Diarrhea is a reported and relatively common side effect of Rituxan, with studies showing incidence rates as high as 17% in some patient populations.
Multiple Causes: Diarrhea can stem from mild gastrointestinal upset, infusion-related reactions, or more serious conditions such as tumor lysis syndrome, infections, or drug-induced colitis.
Serious Signs: Severe diarrhea, especially when accompanied by abdominal pain, fever, or vomiting, can be a symptom of a serious complication like tumor lysis syndrome or colitis and requires urgent medical attention.
Management Strategies: Mild cases can often be managed through increased fluid intake, dietary adjustments (like the BRAT diet), and, with a doctor's approval, OTC anti-diarrhea medications.
Professional Guidance is Key: Patients experiencing diarrhea while on Rituxan should inform their healthcare provider to determine the cause and the most appropriate course of action.
Combination Therapy: Other medications given with Rituxan, such as chemotherapy, can contribute to or worsen gastrointestinal side effects like diarrhea.

Rituxan (rituximab) is a monoclonal antibody used to treat various conditions, including non-Hodgkin's lymphoma (NHL), chronic lymphocytic leukemia (CLL), rheumatoid arthritis (RA), and certain types of vasculitis. As a targeted therapy, it works by binding to a specific protein called CD20 on the surface of B-cells, leading to their depletion. While effective in treating these diseases, this mechanism can also lead to a range of side effects, including gastrointestinal issues like diarrhea.

Is diarrhea a common side effect of Rituxan?

Yes, diarrhea is a known and reported side effect of Rituxan. Clinical trial data indicate that a notable percentage of patients experience this adverse effect. It is often included in the list of mild to moderate side effects associated with the drug.

Incidence varies by indication: For instance, in studies for certain types of vasculitis (GPA and MPA), diarrhea was listed as one of the common side effects, alongside nausea, headache, and muscle spasms.
Connection to infusion reactions: Diarrhea can also be part of a broader set of symptoms associated with infusion-related reactions, which are very common, particularly during the first infusion. These reactions can include fever, chills, nausea, and headaches, in addition to gastrointestinal distress.

What causes diarrhea when taking Rituxan?

Diarrhea associated with Rituxan is not always caused by a single mechanism. The underlying reason can range from simple gastrointestinal upset to more serious conditions that require immediate medical attention. It is crucial for patients and their healthcare providers to differentiate between these potential causes.

Common gastrointestinal upset: The body's reaction to a new medication, especially one administered intravenously, can simply cause temporary stomach upset and loose stools. This is often mild and resolves on its own or with supportive care.
Tumor lysis syndrome (TLS): For cancer patients, particularly those with a large tumor burden, Rituxan's rapid destruction of cancer cells can release high levels of cellular contents into the bloodstream. This can lead to serious metabolic complications and can manifest with severe nausea, vomiting, and diarrhea. TLS typically occurs within 12 to 24 hours after an infusion.
Rituximab-associated colitis: In rare cases, Rituxan has been associated with the development of drug-induced colitis, an inflammation of the colon. Studies have noted that a small percentage of patients who received Rituxan and later underwent a colonoscopy were diagnosed with colitis. Symptoms can include persistent diarrhea, abdominal pain, and sometimes weight loss.
Infections: Because Rituxan depletes B-cells and can affect the immune system, it increases the risk of serious infections. These infections, both bacterial and viral, can cause diarrhea and other gastrointestinal symptoms.
Combination therapies: Diarrhea and other gastrointestinal problems can also be exacerbated or caused by other medications given alongside Rituxan, such as chemotherapy drugs.

Comparison of Rituxan-Associated Diarrhea Causes


Feature	Common Gastrointestinal Upset	Tumor Lysis Syndrome (TLS)	Rituximab-Associated Colitis
Onset	Often during or shortly after the infusion.	Within 12-24 hours of the first infusion.	Can occur months after Rituxan treatment has started or even ended.
Severity	Typically mild and temporary.	Can be severe, with potential for fatal outcomes if not treated.	Varies from mild to severe, and in rare cases, can lead to intestinal perforation.
Associated Symptoms	Nausea, vomiting, headache, fever.	Nausea, vomiting, lack of energy, and electrolyte abnormalities.	Abdominal pain, weight loss, and possibly bloody stools.
Primary Cause	A common reaction to the medication itself.	Rapid breakdown of cancer cells.	Depletion of B-cells leading to immune dysregulation in the gut.

Managing diarrhea related to Rituxan treatment

Your healthcare provider is the best resource for managing side effects, but there are some general strategies that can help with mild diarrhea.

Dietary and hydration management

Stay hydrated: Drink plenty of fluids like water, broth, and sports drinks to replace lost electrolytes and prevent dehydration.
Follow the BRAT diet: The BRAT diet (bananas, rice, applesauce, and toast) consists of bland foods that can help bind your stool.
Avoid trigger foods: Steer clear of greasy, spicy, or high-fiber foods that can irritate the digestive system and worsen symptoms.
Limit alcohol: Alcohol can aggravate gastrointestinal side effects and should be limited or avoided.
Eat small, frequent meals: Large meals can overwhelm the digestive system. Eating smaller amounts throughout the day can be easier to tolerate.

Medical management

Over-the-counter (OTC) medications: Your doctor may recommend an OTC anti-diarrhea medicine like loperamide (Imodium). Crucially, do not take any new medication without first consulting your doctor to ensure it is safe to combine with your Rituxan treatment.
Prescription medications: For more persistent or severe cases, or if colitis is diagnosed, your doctor may prescribe other medications, such as corticosteroids, to manage the inflammation.

When to contact your doctor

While some diarrhea can be managed at home, certain symptoms warrant immediate medical attention. You should contact your healthcare provider right away if you experience:

Frequent or severe diarrhea that does not improve.
Diarrhea accompanied by severe abdominal pain or cramping.
Vomiting that prevents you from keeping fluids down.
Signs of dehydration, such as dizziness, reduced urination, or extreme thirst.
Fever or signs of a new infection.
Bloody stools.

Conclusion

In summary, the answer to the question, Does Rituxan cause diarrhea? is a definite yes. Diarrhea is a recognized side effect that can range from a temporary, mild annoyance to a sign of a serious medical condition like tumor lysis syndrome or colitis. While mild cases can often be managed with supportive care, hydration, and dietary adjustments, it is vital to communicate any persistent or severe symptoms to your healthcare team. Prompt evaluation and appropriate treatment are essential to ensure patient safety and well-being during Rituxan therapy. Remember that Rituxan can cause various side effects, and close collaboration with your doctor will lead to the best possible outcomes.

For more detailed information on drug interactions and side effects, you can visit the U.S. National Library of Medicine's MedlinePlus drug information page for Rituximab.

Frequently Asked Questions

Clinical trial data indicates that diarrhea is a relatively common side effect of Rituxan. For patients with conditions like non-Hodgkin's lymphoma (NHL), granulomatosis with polyangiitis (GPA), and microscopic polyangiitis (MPA), studies have reported incidence rates of diarrhea ranging from 10% to 17%.

Diarrhea and other gastrointestinal side effects can occur during or shortly after the Rituxan infusion, sometimes as part of an infusion-related reaction. However, in some rare cases of drug-induced colitis, diarrhea can appear months after treatment has started.

While often mild, diarrhea can be a sign of a serious side effect. In cancer patients, it can indicate tumor lysis syndrome (TLS), a rapid breakdown of cancer cells. Persistent or bloody diarrhea may also point towards a serious infection or drug-induced colitis.

Tumor lysis syndrome (TLS) is a serious, potentially fatal condition that can occur when Rituxan rapidly kills cancer cells, causing them to release their contents into the blood. This can lead to metabolic imbalances, with diarrhea being one of the key symptoms, often along with nausea and vomiting.

While not always preventable, premedication with an antihistamine and acetaminophen before each Rituxan infusion can help lessen the risk of certain side effects, including some components of infusion reactions that cause gastrointestinal distress. Discussing preventative measures with your doctor is the best approach.

For mild diarrhea, following a bland diet, like the BRAT diet (bananas, rice, applesauce, and toast), and avoiding fatty, spicy, or high-fiber foods can help. It is also crucial to stay well-hydrated by drinking plenty of water and electrolyte-rich fluids.

You should contact your healthcare provider immediately if you experience persistent or severe diarrhea, especially if accompanied by fever, severe abdominal pain, bloody stools, or signs of dehydration (e.g., decreased urination, dizziness).