Lomustine (generic name; also called CCNU; brand name CeeNU) is a prescription chemotherapy drug for dogs. It’s a nitrosourea alkylating agent—plainly, it damages cancer-cell DNA. Rx-only.
Commonly prescribed for: mast cell tumors, certain lymphomas (often relapsed/refractory), and histiocytic sarcoma in dogs. Your veterinarian can discuss why it was chosen for your dog and the monitoring plan.
Key safety note for reception triage: chemotherapy with lomustine can lower white blood cells and can affect the liver. If an owner reports fever, unusual bruising/bleeding, or yellow gums/eyes, advise immediate veterinary evaluation; if after hours, direct them to an emergency hospital.
Front desk script: Lomustine—also called CCNU or CeeNU—is a prescription chemotherapy used in dogs, commonly for mast cell tumors, some lymphomas, and histiocytic sarcoma. It’s a chemo drug that works by damaging cancer-cell DNA. Your veterinarian can explain how it fits your dog’s plan and what monitoring is needed. If you notice fever, unusual bruising or bleeding, or yellow gums/eyes, please contact us right away or go to the emergency clinic after hours.
Lomustine (CCNU) is an oral chemotherapy used in dogs for certain cancers. Owners most often ask: “How will my dog feel after a dose?” Mild stomach upset (less appetite, vomiting, diarrhea) can happen and usually lasts a few days; your veterinarian can provide anti-nausea plans and monitoring instructions. “What warning signs should I watch for?” Call right away for fever, severe tiredness, bruising/bleeding, trouble breathing, or yellow gums/eyes—these can signal low blood counts or liver problems and need urgent care. “How do I handle the capsules and my dog’s waste?” Wear disposable gloves, do not open or crush capsules, and keep medication away from children, pregnant/nursing people, and immunocompromised individuals. Handle urine/feces/vomit with gloves for 2–3 days after a dose, double-bag waste, and wash hands afterward; ask your veterinarian for clinic-specific safety instructions.
Other common questions: “What if I miss or my dog spits out a dose?” Do not give an extra dose—call the veterinary team for exact next steps. “Will my dog lose hair?” Some dogs can have hair coat/whisker changes; many do not. “Why are blood tests needed?” Lomustine can lower white cells and platelets and can affect the liver; your veterinarian will schedule blood and liver checks before and after doses and adjust the plan as needed.
Front desk script: Lomustine is a chemo capsule for certain cancers. Some dogs get mild tummy upset for a few days—please call us if vomiting, diarrhea, or not eating lasts or worsens. If you see fever, severe lethargy, bruising/bleeding, trouble breathing, or yellow gums/eyes, go to the nearest emergency vet now and let us know. Please wear gloves to handle the capsule and your dog’s urine or stool for the next 2–3 days, and don’t open or crush the capsule. If a dose is missed or spit out, don’t re-dose—call us so the veterinarian can advise you.
What owners most often report in the first few days after a lomustine dose are “tummy” issues and low energy: reduced appetite, nausea, vomiting, or soft stool/diarrhea. These mild signs typically start within 1–3 days after the dose and last a day or two. Less commonly, owners may notice mouth sores or some coat thinning. Your veterinarian can discuss what’s expected for your dog based on their specific plan. ([avim.us](https://www.avim.us/chemotherapy-in-small-animals))
More serious but uncommon reactions can occur later. Around days 7–10 after a dose (and sometimes again near day 21), white blood cells and/or platelets may be low; owners might report fever, extreme tiredness, not wanting to get up, bruising, or nose/gum bleeding. Call the clinic the same day if your dog vomits or has diarrhea more than three times in a day, if there is blood in stool or vomit, or if appetite remains poor for more than 48 hours. Treat any rectal temperature over 103°F, collapse, trouble breathing, or severe lethargy as an emergency and seek immediate care. Your veterinarian will advise you on the timing of post‑treatment blood checks and what to watch for at home. ([cliniciansbrief.com](https://www.cliniciansbrief.com/article/commonly-used-chemotherapy-drugs-part-1))
Lomustine can also cause delayed, cumulative liver injury over weeks to months of therapy. Owners may describe new vomiting, poor appetite, increased thirst/urination, a swollen belly, or yellow eyes/gums—these warrant a same‑day call; yellowing, collapse, or breathing trouble are emergencies. Your veterinarian can discuss the clinic’s plan for ongoing liver monitoring. ([pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/14765735/?utm_source=openai))
Front desk script: Some mild stomach upset or lower energy in the first 1–3 days after lomustine can be expected. Please call us the same day if your dog vomits or has diarrhea more than three times in a day, if you see blood in stool or vomit, or if your dog won’t eat for more than 48 hours. If you can take a temperature and it’s over 103°F, or if you see collapse, trouble breathing, bruising/bleeding, or yellow eyes or gums, go to the nearest emergency clinic now and call us on the way. About a week after each dose (and sometimes again around day 21), infection risk can be higher—any fever or extreme lethargy at those times is urgent. Your veterinarian can go over the exact monitoring schedule and what is normal for your dog.
Lomustine is an oral chemotherapy given as a capsule. It must be swallowed whole—do not split, crush, or open the capsule. Give with a small meal or treat to help reduce stomach upset and help it go down, and wear disposable gloves when handling the medication or cleaning up urine, stool, or vomit for the next few days. Pregnant or nursing people and children should not handle this drug or contaminated waste. Follow your veterinarian’s label directions if they differ. ([vcahospitals.com](https://vcahospitals.com/foster/know-your-pet/lomustine))
Pilling tips: offer a few plain treats first, then the capsule hidden in a small soft “meatball,” pill pocket, or a dab of canned food, and immediately follow with the rest of the meal to encourage a quick swallow. Avoid crumbly foods that encourage chewing, and give the dose in an easy-to-clean area. If a capsule is dropped, breaks, or spills, put on gloves, avoid skin contact, and call the clinic for cleanup instructions—do not try to manipulate the contents. ([avim.us](https://www.avim.us/chemotherapy-in-small-animals))
Troubleshooting: if the dog vomits after the dose or refuses the capsule, call the veterinarian before giving any more medication. Seek urgent care if vomiting is persistent, there is blood in vomit or stool, your dog is very weak, or the temperature is 103°F (39.4°C) or higher. If pilling remains difficult, your veterinarian can discuss compounding options (for example, chewables or custom‑strength capsules) and whether they are appropriate; note that some compounded lomustine products have shown variable potency, so the oncology team will guide the safest choice. ([cvm.msu.edu](https://cvm.msu.edu/hospital/services/oncology/care-at-home))
Front desk script: “Lomustine is a chemo capsule that should be swallowed whole. Give it with a small meal or soft treat, and please use gloves—don’t open or crush the capsule. If your dog vomits after the dose or you can’t get the capsule down, please call us before giving any more; if vomiting continues, there’s blood, your dog seems very weak, or the temperature is 103°F or higher, go to urgent care. If pilling is a struggle, our veterinarian can discuss safer compounding options for your dog.”
Lomustine (CCNU) is an oral chemotherapy for dogs that requires laboratory monitoring before each dose. The veterinarian typically reviews a complete blood count about one week after a dose and again before the next dose, plus liver/kidney tests before the next scheduled dose; this is because lomustine can suppress white blood cells on a delay and has a known risk for cumulative liver injury. Because of these safety checks, refills are not automatic and must be approved by a veterinarian for each cycle. Your veterinarian can advise if a re-exam is needed based on how recently the pet was seen and the most recent lab results.
When taking a refill call, collect: pet name/owner, weight changes, date of last dose, number of capsules left, any side effects since the last dose (especially fever, bruising/bleeding, yellow gums/eyes, vomiting/diarrhea, severe lethargy), current medications/supplements, and the pharmacy preference (in-house vs. outside/compounding). Standard turnaround is 1–2 business days for doctor review; compounding or online pharmacy fulfillment may add several days for processing and shipping. For outside pharmacies, confirm exact drug name (lomustine), capsule strength, and that the pharmacy can handle hazardous drugs; send prescriptions directly to the pharmacy rather than handing them to clients when possible.
Escalate immediately if the caller reports red-flag signs such as fever, bruising/bleeding, yellowing of the eyes or gums, or severe lethargy—these can be urgent chemo-related problems. Do not give dosing advice or tell the client to skip/give a dose; route to the veterinarian for guidance and same-day triage if concerning signs are present.
Front desk script: Thanks for calling about a lomustine refill. Because this is chemotherapy, our doctor must review your pet’s most recent bloodwork before approving each dose. Can I confirm your dog’s last dose date, how many capsules you have left, any new meds, and whether you’ve seen fever, bruising/bleeding, yellow gums/eyes, vomiting/diarrhea, or unusual tiredness? If any of those are happening now, we want to get your dog seen today or direct you to emergency care. Refill review usually takes 1–2 business days; if you prefer an outside or compounding pharmacy, shipping can add a few days.
Lomustine can cause dangerous drops in infection‑fighting white blood cells and platelets after a dose; this may appear about a week later and can be delayed for several weeks. Escalate immediately for fever, shaking or collapse, extreme lethargy, not eating, new bruising, nosebleeds, bleeding from the mouth, blood in urine, or black/tarry stools—these can signal infection or bleeding and need urgent veterinary assessment.
Lomustine can also injure the liver and the risk can build over time, even weeks to months into therapy. Urgently escalate for yellow eyes, gums, or skin; dark urine; a swollen belly; persistent vomiting or diarrhea; refusal to eat; or marked lethargy—these may indicate serious liver problems. Your veterinarian can discuss what monitoring to expect and which side effects are anticipated for your dog.
Severe allergic reactions can happen at any time: sudden hives, facial swelling, or trouble breathing are emergencies. Suspected overdose or extra doses are life‑threatening; the warning signs overlap above (weakness, fever, bleeding, vomiting or diarrhea, coughing or difficulty breathing, yellow eyes/gums). Stop the conversation and get a veterinarian or technician immediately; if after hours, direct to an emergency hospital. You may also provide poison control options for guidance during transport.
Front desk script: Because this is lomustine, those signs can be an emergency. I’m getting a veterinarian or technician on the line now—please come to the hospital or the nearest emergency clinic immediately. If you think an extra dose was given or a capsule was chewed, bring the packaging and head in now. If you need help en route or it’s after hours, you can also call Pet Poison Helpline at 855-764-7661 or ASPCA Animal Poison Control at 888-426-4435.
Key interaction flags: Lomustine can strongly lower blood cell counts and can injure the liver. Flag any added drugs that also suppress the bone marrow (other chemotherapy; some antibiotics such as chloramphenicol) or suppress the immune system (e.g., corticosteroids like prednisone, azathioprine), because infection risk can increase. Vaccines—especially live/modified‑live—should be timed by the veterinarian during chemotherapy; do not schedule without checking. Because lomustine is hepatotoxic in dogs, alert the doctor to other liver‑stress medicines or supplements (e.g., acetaminophen products; certain antifungals like ketoconazole) so they can assess safety.
Commonly co‑prescribed/supportive meds you may hear: anti‑nausea drugs (maropitant, ondansetron), antibiotics around expected low white‑cell periods (e.g., amoxicillin‑clavulanate; sometimes trimethoprim‑sulfa per oncologist direction), corticosteroids in some cancer protocols, and liver‑support supplements (e.g., SAMe/silybin products). These can be appropriate but still require charting and veterinarian review for timing and monitoring. Your veterinarian can discuss which combinations are intended and what lab checks are needed.
OTC human products owners often mention: pain/fever reducers (ibuprofen, naproxen, aspirin, acetaminophen) and multi‑symptom cold/flu meds that contain acetaminophen. These can cause GI bleeding, affect platelets, or stress the liver—important concerns when a dog is on lomustine—so document and escalate to the veterinarian before any use. If an owner reports bruising, bleeding, black/tarry stool, fever, severe lethargy, or yellow gums/eyes, advise immediate emergency evaluation and notify the medical team right away.
Front desk script: Thanks for telling me about the other medication. Because lomustine can lower blood counts and affect the liver, our doctor needs to review anything else your dog is getting before we proceed. I’ll add this to the chart and have the veterinarian advise you on what’s safe to use together. If you notice bruising, bleeding, a fever, or yellow gums/eyes, please head to the nearest emergency hospital now and call us on the way.
Store lomustine capsules at room temperature (about 68–77°F/20–25°C) in the original, tightly closed, labeled container. Keep dry, protect from light, and keep out of reach of children and other pets; do not place in pill organizers. Avoid heat and humidity (bathrooms, cars) and do not expose to temperatures above ~104°F. For compounded products, follow the compounding pharmacy’s label. A specific “after opening” shelf life is not published; use until the labeled expiration date if stored properly, or ask the dispensing pharmacy.
Handling: Lomustine is a chemotherapy drug. Do not split, crush, or open capsules. Staff and owners should avoid touching capsules directly; use disposable gloves, then wash hands after handling. Pregnant or nursing people should not handle lomustine or pet waste from treated animals. If a capsule breaks or powder spills, don gloves, avoid skin contact, carefully contain the pieces and any cleanup materials in a sealed bag, clean the surface with household detergent (then disinfect if clinic protocol requires), and return the waste to the clinic/pharmacy for hazardous disposal. Do not flush or throw lomustine capsules in household trash—ask where to return unused or damaged medication.
After dosing at home, advise owners to treat urine and feces as potentially contaminated for at least the first 72 hours; wear gloves for cleanup, wash hands afterward, launder soiled items separately, and use a low‑traffic outdoor area for elimination when possible. Some oncology teams may recommend a longer window for oral chemotherapy; your veterinarian can discuss the time frame and any added precautions for this dog’s regimen. Seek immediate help if a child, another pet, or anyone accidentally swallows a capsule; if skin contact with capsule contents occurs, wash with soap and water and contact a medical professional or poison control.
Before the first lomustine dose, schedule baseline bloodwork as directed (typically a complete blood count and liver/kidney values). After each dose, book two check-ins: a lab-only visit about 1 week after dosing to look for the expected low point in white blood cells (timing can vary and may fall 1–3 weeks after treatment), and a recheck with bloodwork right before the next planned dose. The veterinarian will set the exact dates for each patient and advise if any additional tests are needed.
Because lomustine can affect the liver over time, plan liver enzyme monitoring prior to each dose and as the veterinarian requests. Some dogs can show liver changes weeks after a dose, so the care team may schedule extra bloodwork between cycles or even after treatment ends. Your veterinarian can discuss whether any imaging or advanced testing is appropriate based on results and the cancer being treated.
Escalate immediately if owners report red-flag signs: fever, extreme tiredness, not eating, vomiting or diarrhea lasting more than 24 hours, pale gums, unexpected bruising/bleeding, or yellow gums/eyes. In these situations, arrange same-day evaluation; if after hours, direct them to the nearest emergency hospital. The purpose of these monitoring visits is safety—quick blood tests help confirm it’s safe to stay on schedule and guide any changes the veterinarian may recommend.
Front desk script: For lomustine, we schedule two monitoring visits each cycle: a quick blood test about one week after the dose, and another exam with bloodwork right before the next dose. We’ll also keep checking liver values throughout treatment because this medication can affect the liver over time. If you notice fever, marked tiredness, bruising/bleeding, or yellow gums/eyes, please contact us immediately—after hours, go to the nearest emergency hospital. The veterinarian will confirm exact dates and any additional tests based on your dog’s results.
Lomustine (also called CCNU) is an oral chemotherapy used in dogs. It is a hazardous drug, so pet parents should use gloves when handling the capsules and when cleaning up urine, stool, vomit, or saliva for a few days after dosing, and wash hands after removal. Only the veterinarian can direct how and when it is given; our role is to provide safe handling reminders and help with scheduling.
What owners most ask: “What should I watch for?” Explain that mild tummy upset or tiredness can occur. Urgent signs that need a same‑day call to the care team include bruising or bleeding, fever, not eating, repeated vomiting or diarrhea, yellow eyes or gums, or trouble breathing. Because lomustine can lower white blood cells, the care team may schedule lab checks about one week after a dose and again before the next dose; exact timing is set by the veterinarian. If serious signs are reported, escalate immediately to a nurse/doctor; if collapse, severe breathing trouble, or uncontrolled bleeding is described, direct the caller to the nearest emergency hospital while keeping them on the line as you connect them.
Phrases to avoid: “It’s safe to keep giving it,” “start/stop the medication,” “double the dose if one is missed,” or “you can wait a few days.” Preferred framing: “I can’t advise on dosing or stopping chemotherapy; your veterinarian will discuss that with you. Let me connect you with a nurse right away.”
Front desk script: “Thank you for calling [Hospital Name], this is [Your Name]. I’m happy to help with your dog’s lomustine.” “The most common question is what to watch for—tiredness or mild stomach upset can happen, but bruising or bleeding, fever, not eating, repeated vomiting/diarrhea, yellow gums or eyes, or trouble breathing are urgent.” “I can’t advise on dosing or stopping chemotherapy—your veterinarian will guide that; let me get a nurse or the doctor on the line.” “If you’re calling to schedule monitoring, the team typically checks blood about a week after a dose and again before the next one; I can find the soonest appointment or confirm the plan your veterinarian set.”