Diarrhea During Cancer Treatment

Diarrhea in cancer care is graded on a formal scale, the CTCAE, version 5. The grade is not medical jargon for its own sake. It decides whether treatment continues, is delayed, or is stopped, and whether you get admitted.

The scale counts stools above your own baseline, not stools in total. That distinction matters if you normally go twice a day or once every two days.

• Grade 1: fewer than 4 extra stools a day over baseline, or a mild rise in ostomy output.
• Grade 2: 4 to 6 extra stools a day, or a moderate rise in ostomy output. Everyday tasks like shopping and cooking get harder.
• Grade 3: 7 or more extra stools a day, hospital admission needed, or a severe rise in ostomy output. Self-care such as bathing and dressing is limited.
• Grade 4: life-threatening, needing urgent intervention.

So the useful thing to track is a tally, not an impression. Write down the time of each stool and whether it was loose or watery. A count of "about 8 today, up from my usual 1" gets a very different response than "quite a lot."

The most common trigger is the treatment itself, but different treatments cause it in different ways.

Fluoropyrimidines and irinotecan. Regimens containing 5-FU, capecitabine, or irinotecan cause diarrhea in as many as 50 to 80 percent of people. This is direct damage to the gut lining.

Immune checkpoint inhibitors. Here the immune system is attacking the bowel lining, and it can escalate to colitis. Rates depend on the drug class. Any-grade diarrhea occurs in 16 to 37 percent of people on a single PD-1 or PD-L1 drug, 32 to 49 percent on a single anti-CTLA-4 drug, and 17 to 44 percent on a dual checkpoint regimen.

Radiation to the abdomen or pelvis. The bowel sits in the treatment field and the lining thins.

Bone marrow transplant. Graft-versus-host disease of the gut is one cause, and it needs its own treatment.

Surgery on the gut. Removing bowel changes transit time and bile handling permanently.

Infection. Clostridioides difficile is a common cause of pseudomembranous colitis, especially after antibiotics. This one is important, because the treatment for infection is close to the opposite of the treatment for ordinary chemotherapy diarrhea.

Other causes get missed: tube feeding, laxatives that were not adjusted, magnesium supplements, and stool leaking around a blockage. That last one looks like diarrhea and is actually constipation.

Loperamide is an opioid that acts on the gut without much effect on the brain. Two dosing patterns appear in cancer guidance, and they are not the same.

General cancer-related diarrhea. Start with 4 mg, then 2 mg after each unformed stool, up to roughly 12 mg per day.

Irinotecan late diarrhea. The irinotecan label uses a higher regimen: 4 mg at the first loose stool, then 2 mg every 2 hours until you have gone 12 hours with none, and 4 mg every 4 hours overnight. That exceeds the usual daily maximum on purpose, and the label warns not to run it beyond 48 consecutive hours because of the risk of paralytic ileus, a stalled bowel.

Do not assume the higher schedule applies to you. Ask which one your team wants, and get it in writing.

One honest limitation: loperamide is often not enough for grade 3 or 4 diarrhea. If you are past 7 extra stools a day, more loperamide is unlikely to be the answer, and calling is.

Bulk-forming agents such as psyllium are widely used, but there is little evidence they help here, and the large volume needed often causes bloating.

Adsorbents such as kaolin, clay, and activated charcoal have been used extensively without data to support them. Worse, they can block the absorption of the anti-diarrheal drugs that do work.

Bismuth subsalicylate (Pepto-Bismol) is off the table if you cannot take aspirin, and large doses can cause salicylate toxicity.

Octreotide, a hormone-blocking injection, and corticosteroids have specific roles chosen by your team. They are not self-care items.

Replace what you are losing. Diarrhea sheds sodium and potassium as well as water, so plain water alone is not enough. Oral rehydration solutions, broth, and diluted sports drinks all help.

Cut lactose, high-fat food, caffeine, alcohol, and sugar alcohols such as sorbitol while symptoms are active. Small, frequent meals are easier than three large ones.

Protect the skin. Rinse with warm water rather than wiping, pat dry, and use a barrier cream.

If your diarrhea began during or shortly after an immune checkpoint inhibitor, say so on the phone. Immune colitis is usually treated with corticosteroids, and anti-diarrheal drugs alone can mask a worsening picture.

If you have had antibiotics recently, ask whether a stool test for C. difficile should be sent before anything is prescribed to slow the gut.

• 7 or more stools a day above your normal, or grade 3 by your team's counting
• Any fever at 100.4 F (38 C) or higher alongside diarrhea
• Blood in the stool, black tarry stool, or mucus with severe cramping
• Not passing urine for 8 hours, or feeling faint when standing
• Vomiting so that you cannot keep fluids down for more than 12 hours
• Belly pain that is severe, constant, or with a swollen rigid abdomen
• More than 24 hours of loperamide with no improvement

Immunotherapy Colitis: What to Ask, Mucositis During Cancer Treatment, Nutrition During Treatment, and Fever During Chemo.

• https://www.cancer.gov/about-cancer/treatment/side-effects/constipation/GI-complications-hp-pdq
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e518dfc6-7e93-4fee-a66c-51e1ab71c056
• https://www.cancer.gov/about-cancer/treatment/side-effects/diarrhea