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Lonsurf: Side effects

Lonsurf is usually used as a third-line chemotherapy drug, after a patient has had tumor growth on FOLFOX and FOLFIRI or FOLFOXIRI. Studies have shown that Lonsurf may be more effective when given with Avastin. So sometimes it can be difficult to tell which side effects come from which medications!

Lonsurf can come along with a bunch of unpleasant side effects. If you’re on a Lonsurf regimen, here are some side effects you might experience:

Whew, sounds like a lot, right? Remember that you likely won’t experience all of these side effects — because everyone’s bodies are different. 

If you ever feel like you can’t manage your side effects and symptoms, don’t be afraid to speak with your doctor about pre-meds or complimentary meds to manage them. You can also ask for a referral to the palliative care specialist or team at your cancer center. It’s important to note that palliative care is not the same as hospice care. Palliative care helps patients manage symptoms, and it can be extremely helpful for many people.

Remember that it’s important to check in with your healthcare team before starting any supplements, complementary therapies or fasting regimens. These treatments might not be appropriate for everyone — and some may even interfere with chemotherapy.

Let’s get into some side effects you might experience…

Want to learn more about Lonsurf?

Click here to go to the Lonsurf website. There are lots of patient resources, including information about the drug, a brochure for carepartners, a starter kit, and other helpful resources.

Nausea or vomiting

This is an extremely common chemotherapy side effect. Nausea usually lasts for a few days to a week after treatment.

Here are some tips: 
  • Take pre-meds. Your oncologist will likely prescribe anti-nausea medications like dexamethasone, Compazine, Zofran, Ativan, and Akynzeo. Even if you don’t feel sick, take your medications as prescribed. It’s much easier to prevent nausea than it is to treat it once it has started
  • Stay well hydrated. Drinking plenty of water and receiving fluids post-treatment can help with nausea
  • Eat a small amount of bland food, like rice or bread
  • Choose foods that sound appealing to you. If you’re craving Cheetos, follow your gut. Avoid foods with strong smells
  • Try ginger tea, candies or gummies
  • Try acupuncture or acupressure
  • Look into deep breathing or muscle relaxation techniques


Lonsurf can cause loose bowels. You may experience this at any point during your treatment, even up to 10 days post-treatment.

Here are some tips:
  • Make sure to stay hydrated. Drink plenty of water and consider drinks with electrolytes
  • You may be given atropine as a pre-med to help prevent diarrhea
  • You can also take over the counter medications such as Immodium or Lomitil at home to help manage symptoms

Stomach cramps

Some patients report experiencing stomach cramps with Lonsurf.

Here are some tips:
  • Ask your oncologist about medications such as Atropine, Lotomil (which contains Atropine and can be taken at home), or Bentyl
  • Try a heating pad on the stomach
  • Take a warm bath

Hair thinning or loss

When you first learned about starting chemotherapy, you might have been worried about losing your beautiful hair! However, colorectal cancer patients undergoing chemo often experience hair thinning, not complete hair loss.

Here are some tips:
  • Purchase a cold cap. Reducing the temperature of your scalp can prevent chemotherapy drugs from attacking your hair follicles
  • Get a good quality wig. You might not need it, but it can help you feel more confident. Many insurance companies will help cover the cost of a medical wig. There are several organizations that work specifically with cancer patients. They can often help advise how to get the cost of the wig covered by your insurance and some companies can even make custom wigs from your own hair! If you are interested, here are some organizations to check out: Wigs and WishesCompassionate CreationsChemo DivaCaring and Comfort
  • Use a good quality shampoo and conditioner. Join COLONTOWN, where you will find some good brand recommendations!
  • Be gentle on your hair! Use a wide-toothed comb, and if you get tangles, don’t pull too hard. Protect your hair while you are sleeping

Want to learn more about coping with hair loss?

Check out this link from the National Cancer Institute.

Loss of appetite

Chemotherapy can change the way your body perceives tastes and smells, causing aversions to things you usually don’t mind! These changes are temporary, and will likely go away after chemo has finished or if you have a chemo break.

Here are some tips:
  • Avoid spicy foods, and foods with strong tastes and smells
  • Try eating 5 to 6 small meals or snacks throughout the day
  • Stay well hydrated. Drinking plenty of water and receiving fluids after your treatment can help with nausea
  • Choose foods that sound appealing to you. If you’re craving Cheetos, follow your gut
  • If this is a persistent problem, speak to your team. They may be able to prescribe medication to help stimulate your appetite


Feeling tired is one of the most common side effects for people going through chemotherapy. It’s important to remember that your body is going through a lot.

Here are some tips:
  • Listen to your body. Take naps and rest when you need to
  • Try some light exercises. Going for a walk can help raise your energy levels
  • Notice patterns in your chemo cycle. Do your best to plan activities that require a lot of energy on the days you normally feel best
  • Ask friends and family to help with things like cooking, childcare, shopping and housework. Gift certificates for cleaning services or food delivery can be great gifts to ask for


Lonsurf can be particularly hard on blood counts and platelets, so fever may be a common side effect.

Here are some tips:
  • Make sure to drink plenty of fluids and stay well hydrated
  • Get plenty of rest
  • Monitor your temperature on a regular basis, and keep an eye out for signs of infection
  • Call your doctor if you have signs of infection, or a high fever that does not improve with Tylenol or Advil

Low white blood cell counts

White blood cells (WBC) are used to fight off infections. Low white blood cell counts can increase your risk of infection, and make you feel short of breath.

Your healthcare team will monitor your WBC counts to make sure they don’t get too low. If they are, your treatment might be delayed by a week or two, to give your body a chance to recover. Treatment delays should be avoided whenever possible, but they are common.

Talk to your team about any concerns you have, but know that an occasional chemo delay should not affect your long-term prognosis or the overall effectiveness of your treatment.

Here are some tips:
  • Protect yourself from infection. Wash your hands regularly, and avoid contact with people who have contagious illnesses
  • Eat a well-balanced diet, with plenty of healthy proteins. Wash your produce well, and cook food thoroughly to avoid bacterial infections. Avoid uncooked, unpasteurized and undercooked foods
  • Try light to moderate exercise
  • Your doctor may prescribe injections like filgrastim (Neupogen), fligrastim biosimilar (Zarxio), pegfilgrastim (Neulasta), and pegfilgrastim biosimilar (Udenyca) can boost white blood cell counts and help you avoid treatment delays. However, these injections can cause bone pain. Try taking Claritin to help.

Low red blood cell counts

Chemotherapy will likely decrease your red blood cell (RBC) counts. This can cause fatigue and shortness of breath. Your healthcare team will monitor your RBC levels to make sure they don’t go too low. Many patients diagnosed with colorectal cancer may already have anemia due to iron deficiency from tumors in the gastrointestinal tract bleeding. Chemo can worsen preexisting anemia. 

Here are some tips:
  • Get your ferritin levels tested to assess the level of iron stores in your blood — especially if you suspect iron-deficiency anemia. If you have low ferritin levels, your oncologist may recommend iron supplements
  • If there are other reasons for blood loss such as heavy periods, make sure to address this!
  • If your ferritin levels are normal, but your RBC counts are very low, your oncologist might recommend a blood transfusion
  • Injections, such as Procrit, can help boost RBC counts

Low platelets

Chemotherapy drugs can cause your platelet levels to drop. Platelets help your blood clot — so low levels can cause bruising, nosebleeds and sensitive gums.

Here are some tips:
  • Sometimes, low platelet counts can be caused by problems with the spleen. In this case, the problem may be resolved by a minimally invasive procedure called splenic embolization. This is not appropriate for everyone, so please speak to your healthcare team if you have any questions
  • Your doctor may prescribe injections, such as  romiplostim (Nplate) and eltrombopag (Promacta) which can help boost platelet counts
  • Some patients are given platelet infusions

When should I contact my care team?

It’s a good idea to keep a journal or notes about your side effects, so you can discuss them with your oncologist at your next appointment. This can help you advocate for changes to your pre-meds and home meds as necessary. Be sure to discuss possible side effects with your oncologist, so you know what’s normal and what might be concerning. Before your first chemo treatment, you should have been given a 24-hour phone number to call in case of severe symptoms.

Some of these symptoms include:

  • Persistent high fever
  • Chest pain or chest discomfort
  • Unexplained bruising or bleeding that won’t stop
  • Shortness of breath
  • Unusual or intense pain
  • Signs of an allergic reaction, such as severe itching, swollen tongue, or difficulty swallowing
  • Persistent diarrhea or vomiting

Want to learn more about side effects and how to manage them?

Join one of our COLONTOWN Facebook groups:

  • In the Long Haulers Hollow group, we discuss all things related to Lonsurf chemo
  • Corner Cupboard is a place to discuss treatment side effects and management
  • If you’re suffering from late or long-lasting side effects related to treatment, check out The Late Show
  • Palliative Pathways can teach you how your palliative care team can help you
  • In Healthy Habits Highway, you can learn about how diet and exercise can help improve quality of life during treatment
  • Join Live Wire to learn about icing strategies and ways to cope with neuropathy
  • Cognitive Way is here to help people struggling with chemo brain

Want to join? Fill out the registration form here.

COLONTOWN University has so much more to offer, from DocTalk videos with CRC experts to easy-to-understand biomarker test breakdowns. We’re here for you! See our list of Learning Centers here.

Last updated: February 26, 2023

Chemotherapy And Targeted Therapies