Lomustine (CCNU)

Lomustine, also known as CCNU (1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea) and sold under brand names including Gleostine and CeeNU, is a potent chemotherapy medication belonging to the nitrosourea subclass of alkylating agents. This oral chemotherapy drug has become an important option in feline oncology, particularly valued for its effectiveness against lymphoma and its ability to cross the blood-brain barrier to treat tumors affecting the central nervous system. Lomustine represents one of the few oral chemotherapy agents that can be administered at home, offering convenience for pet owners while maintaining significant anticancer activity.

The mechanism of action of lomustine involves the formation of DNA cross-links and DNA-protein cross-links that disrupt genetic replication and transcription. After oral administration, lomustine is rapidly absorbed from the gastrointestinal tract and metabolized in the liver to active compounds that bind to DNA strands. This binding prevents cancer cells from successfully dividing and replicating, ultimately leading to cell death. Unlike some chemotherapy agents that target only specific phases of cell division, lomustine affects cells throughout the cell cycle, contributing to its broad effectiveness against various tumor types.

Lomustine is highly lipid-soluble, a property that allows it to cross cell membranes easily and penetrate the blood-brain barrier into the central nervous system. This characteristic makes lomustine particularly valuable for treating tumors affecting the brain and spinal cord, where many other chemotherapy drugs cannot reach adequate concentrations. In cats, this property proves useful for certain presentations of lymphoma and for managing tumors with potential central nervous system involvement. The drug achieves therapeutic levels in cerebrospinal fluid, enabling treatment of malignancies that would otherwise be inaccessible to systemic chemotherapy.

Veterinary oncologists utilize lomustine both as a first-line treatment option and as a rescue agent for cats with resistant or relapsed cancers. The medication is administered orally, typically every three to six weeks depending on the protocol, with careful monitoring of blood counts and organ function between treatments. While lomustine offers significant benefits in cancer treatment, it requires close veterinary supervision due to potential serious side effects including bone marrow suppression. Pet owners considering lomustine therapy for their cats should work closely with a veterinary oncologist to understand the expected benefits, risks, and monitoring requirements associated with this important anticancer medication.

Lomustine serves as both a first-line treatment and a rescue agent for feline lymphoma, the most common cancer affecting cats. Studies have demonstrated particular effectiveness for gastrointestinal lymphoma, with response rates of approximately 50% in treatment-naive cats with intermediate to large cell gastrointestinal lymphoma. The medication has shown valuable activity against both alimentary and non-alimentary forms of lymphoma, making it a versatile option in feline oncology. Veterinary oncologists may choose lomustine as initial therapy or reserve it for cats that have failed to respond to or relapsed after standard CHOP or COP protocols.

As a rescue agent for resistant feline lymphoma, lomustine has demonstrated acceptable efficacy and safety. Cats with lymphoma that progresses during or relapses after first-line chemotherapy often have limited treatment options, and lomustine provides a viable alternative in these challenging situations. Studies evaluating lomustine rescue therapy have shown response rates ranging from 26% to 54%, with some cats achieving durable remissions. The medication may be used alone or in combination with other agents as part of multidrug rescue protocols.

Mast cell tumors represent another important indication for lomustine in cats. While surgical removal remains the preferred treatment for localized mast cell tumors, cats with disseminated or non-resectable disease may benefit from chemotherapy. Studies have reported overall response rates of approximately 50% in cats with mast cell tumors treated with lomustine. The medication may help control tumor growth and improve quality of life in cats with aggressive mast cell disease, though prolonged survival specifically attributable to chemotherapy has not been definitively established.

The ability of lomustine to penetrate the blood-brain barrier makes it valuable for treating tumors affecting the central nervous system in cats. Brain tumors, though relatively uncommon in cats, may respond to lomustine when surgery is not feasible. The drug can also be considered for lymphoma with known or suspected central nervous system involvement. This property distinguishes lomustine from many other chemotherapy agents and provides a treatment option for cancers in locations that would otherwise be difficult to reach with systemic therapy.

Veterinary oncologists may select lomustine over alternative chemotherapy agents based on several factors including the specific cancer type, previous treatments received, owner preference for oral administration, and individual patient characteristics. The convenience of oral dosing administered at relatively long intervals (typically every 3-6 weeks) appeals to many cat owners, as it reduces the frequency of veterinary visits and associated stress for the patient. However, the decision to use lomustine requires careful consideration of its toxicity profile and the commitment to appropriate monitoring throughout treatment.

The dosing of lomustine in cats requires careful calculation and strict adherence to veterinary instructions, as this medication has a narrow therapeutic window between effective and toxic doses. Standard dosing in feline patients typically falls in the range of 50-60 mg/m² body surface area, administered orally every four to six weeks. Phase I studies established that cats can tolerate these doses with manageable toxicity when appropriate monitoring is performed. However, individual protocols may vary based on the specific cancer being treated, the cat's overall health, and whether lomustine is used alone or in combination with other agents.

Administration of lomustine should occur with food to decrease the risk of gastrointestinal upset and nausea. The capsules should be swallowed whole without crushing, breaking, or opening, as this protects both the medication's integrity and the handler from drug exposure. Pet owners must wear gloves when handling lomustine capsules and should wash hands thoroughly afterward even with glove use. The exact dose prescribed will depend on the cat's body surface area, calculated from body weight using standard veterinary formulas.

Treatment intervals for lomustine are typically longer than many other chemotherapy agents, commonly ranging from three to six weeks between doses. A six-week dosing interval is often recommended based on phase I studies showing that neutropenia (the primary dose-limiting toxicity) can occur from 7-28 days after treatment and may require up to 14 additional days to resolve. This extended interval allows bone marrow recovery before subsequent treatment. Some protocols, particularly those combining lomustine with other agents, may use modified intervals.

Missing a lomustine dose requires prompt communication with the veterinary oncologist rather than independent action by the pet owner. Because this medication is administered at long intervals as part of carefully designed protocols, the appropriate response to a missed dose depends on specific circumstances. Pet owners should never attempt to make up a missed dose by giving extra medication, as this significantly increases toxicity risk. The veterinary team will provide guidance on rescheduling based on the treatment plan and the cat's condition.

Treatment duration with lomustine varies depending on the cancer type, treatment response, and individual patient factors. Some cats receive a defined number of cycles, while others continue treatment as long as they remain in remission with acceptable quality of life. The decision to continue, modify, or discontinue therapy involves ongoing assessment of treatment response, side effect management, and the cat's overall wellbeing. Regular monitoring appointments are essential throughout the treatment course to ensure safety and optimize outcomes.

Dose modifications may become necessary based on monitoring results or observed toxicities. Cats experiencing significant bone marrow suppression or other serious side effects may require dose reductions, extended treatment intervals, or discontinuation of therapy. Veterinary oncologists follow established guidelines for managing toxicities while attempting to maintain anticancer effectiveness. Pet owners should understand that dose adjustments reflect appropriate medical management rather than treatment failure.

Lomustine is generally well tolerated by cats when administered according to appropriate protocols with proper monitoring, though pet owners should understand the potential side effects associated with this chemotherapy medication. The goal of veterinary cancer treatment is to maintain quality of life while fighting disease, and most cats experience minimal to moderate side effects that can be managed effectively. However, some serious toxicities can occur, making regular monitoring and prompt reporting of symptoms essential.

Bone marrow suppression represents the most significant and dose-limiting toxicity of lomustine in cats. This manifests primarily as neutropenia (decreased white blood cells), thrombocytopenia (decreased platelets), and less commonly as anemia (decreased red blood cells). Neutropenia typically reaches its lowest point (nadir) 7 to 21 days after treatment but can occur up to 28 days later, and recovery may take an additional one to two weeks. During periods of neutropenia, cats face increased susceptibility to infections, and signs such as fever, lethargy, or loss of appetite require immediate veterinary attention. Hematologic monitoring is essential to detect these changes before they become dangerous.

Gastrointestinal side effects including nausea, vomiting, diarrhea, and decreased appetite can occur with lomustine treatment, though these effects are generally uncommon in cats at standard doses. Administering lomustine with food helps minimize gastrointestinal upset. When gastrointestinal symptoms do occur, they are usually mild and self-limiting. Persistent vomiting, severe diarrhea, or prolonged appetite loss warrant veterinary consultation, as supportive medications can often provide relief.

Hepatotoxicity (liver damage) is an important concern with lomustine use in dogs, where chronic irreversible liver failure can occur with repeated dosing. Importantly, hepatotoxicity has not been documented in cats receiving lomustine, representing a significant species difference in drug response. Nevertheless, veterinary oncologists typically recommend monitoring liver enzymes before each treatment as a precaution. This monitoring follows protocols established for dogs, as the absence of reported hepatotoxicity in cats may partly reflect less intensive surveillance rather than true absence of risk.

Rare side effects reported with lomustine include nephrotoxicity (kidney damage), pulmonary toxicity (lung scarring), and delayed bone marrow recovery that becomes cumulative with repeated treatments. Neurological effects are uncommon but possible. Some cats may experience prolonged myelosuppression that requires extending the interval between treatments or discontinuing therapy. Pet owners should monitor their cats for any unusual symptoms and report concerns to their veterinary oncologist promptly. Early detection of side effects enables intervention before they become severe, helping maintain quality of life throughout treatment.

Lomustine should not be administered to cats with known hypersensitivity or previous severe reactions to the medication or related nitrosourea compounds. While allergic reactions to lomustine are uncommon, any cat that has experienced anaphylaxis or other serious hypersensitivity during previous treatment should not receive the drug again. Pet owners should inform the veterinary oncologist of any previous adverse reactions to medications, as this information is essential for safe treatment planning.

Significant bone marrow suppression represents a major contraindication to lomustine administration. Cats with pre-existing neutropenia, thrombocytopenia, or anemia should not receive lomustine until blood counts recover to acceptable levels. The veterinary oncologist will establish specific thresholds for treatment based on individual patient factors and the risks of delaying therapy. Cats whose blood counts fail to recover adequately between scheduled treatments may require protocol modifications or alternative treatment approaches.

Pre-existing liver or kidney disease requires careful evaluation before initiating lomustine therapy. Cats with significant hepatic dysfunction may experience altered drug metabolism, though the clinical implications are not fully characterized. Renal impairment may affect drug clearance and potentially increase toxicity risk. Dose modifications may be necessary for cats with compromised organ function, and some patients may be poor candidates for lomustine therapy. Pre-treatment blood chemistry panels help identify cats requiring special consideration.

Pregnancy and lactation represent absolute contraindications to lomustine use. The drug is teratogenic and embryotoxic, causing fetal abnormalities and death. Nursing queens should not receive lomustine, as the drug or its metabolites may be excreted in milk and harm nursing kittens. Cats intended for breeding should not receive lomustine treatment. Owners of intact cats should discuss reproductive implications with their veterinarian before initiating therapy.

Active serious infections generally preclude lomustine administration until the infection is controlled, as the drug's immunosuppressive effects can worsen infectious conditions and prevent recovery. Cats in very poor body condition or with severe debilitation may not be appropriate candidates for lomustine therapy. The decision to pursue chemotherapy should consider whether the potential benefits outweigh the risks for each individual patient. Complete disclosure of the cat's medical history enables the veterinary oncologist to identify contraindications and design the safest possible treatment approach.

Pet owners must inform the veterinary oncologist of all medications, supplements, and over-the-counter products their cat receives before initiating lomustine therapy. Because lomustine is metabolized in the liver and excreted by the kidneys, drugs affecting these organ systems may interact with lomustine in clinically significant ways. Complete medication disclosure allows the oncology team to anticipate potential interactions and adjust treatment plans accordingly.

Concurrent use of other myelosuppressive drugs with lomustine significantly increases the risk of dangerous bone marrow suppression. This category includes other chemotherapy agents, as well as medications like chloramphenicol that can suppress blood cell production. While combination chemotherapy protocols may intentionally use multiple myelosuppressive agents, these regimens are designed with awareness of cumulative toxicity and incorporate appropriate monitoring and dose adjustments. Adding additional bone marrow-suppressing drugs outside the planned protocol can result in severe neutropenia, anemia, or thrombocytopenia.

Immunosuppressive medications combined with lomustine increase infection risk due to compounded effects on immune function. Corticosteroids like prednisolone are frequently used alongside lomustine in cancer treatment protocols, and these combinations can be managed safely with appropriate monitoring. However, other immunosuppressive drugs used for conditions such as inflammatory bowel disease or immune-mediated diseases may pose greater risks when combined with chemotherapy. The oncology team will evaluate the overall immunosuppressive burden when designing treatment approaches.

Vaccination considerations apply to cats receiving lomustine therapy. Live virus vaccines should be avoided during treatment and for a period afterward, as the immunosuppressed state may allow vaccine viruses to cause disease. Killed vaccines may be administered if essential but may produce suboptimal immune responses. The veterinary team will advise on appropriate vaccination timing based on the treatment schedule and the cat's immune status. Non-essential vaccines should generally be postponed until chemotherapy is complete.

Drug interactions affecting liver enzyme activity may alter lomustine metabolism, though specific interactions have not been extensively studied in cats. Medications known to induce or inhibit hepatic enzymes could theoretically affect lomustine processing and efficacy. Herbal supplements and alternative therapies should also be disclosed, as some natural products have significant effects on liver enzymes and drug metabolism. Pet owners should not add any medications or supplements to their cat's regimen during chemotherapy without veterinary approval, as even seemingly benign products could interact with cancer treatment.

Lomustine is classified as a hazardous drug requiring careful handling by pet owners and veterinary staff to prevent accidental exposure. Pet owners should always wear disposable gloves when handling lomustine capsules and should never open, crush, or break the capsules. If accidental skin contact with capsule contents occurs, the area should be washed immediately and thoroughly with soap and water. Pregnant women, nursing mothers, individuals trying to conceive, and immunocompromised persons should not handle lomustine or come into contact with treated cats' body fluids.

For several days following lomustine administration, the cat's body fluids including urine, feces, vomit, and saliva may contain the drug or its metabolites. Pet owners should wear gloves when cleaning litter boxes and handling accidents during this period. Waste should be sealed in plastic bags before disposal. In multi-cat households, treated cats should ideally use separate litter boxes. Soiled bedding should be laundered separately. If the cat vomits after receiving lomustine, cleanup should be performed wearing gloves with appropriate disposal of contaminated materials.

Regular and consistent monitoring is absolutely essential throughout lomustine treatment. Complete blood counts should be performed one week after dosing and immediately before each subsequent scheduled dose to evaluate bone marrow recovery. Liver and kidney function tests should be conducted before starting treatment and before each dose. Some veterinary oncologists recommend more frequent monitoring during initial treatment cycles. This monitoring schedule allows early detection of toxicities and guides decisions about treatment timing, dosing, and continuation.

Pet owners must recognize warning signs requiring immediate veterinary attention. These include fever (which may indicate infection during neutropenia), persistent vomiting or diarrhea, significant appetite loss or weight loss, lethargy or weakness, bleeding or bruising, pale gums, difficulty breathing, and any other concerning changes. Cats receiving chemotherapy have reduced ability to fight infections, making prompt treatment of illness essential. Pet owners should have emergency veterinary contact information readily available throughout the treatment period.

Special considerations apply to geriatric cats, which represent a significant proportion of feline cancer patients. Older cats may have reduced organ function affecting drug clearance and may be more susceptible to side effects. Pre-treatment evaluation should assess cardiac, hepatic, and renal function. Cats with pre-existing health conditions require careful risk-benefit analysis before initiating lomustine therapy. The veterinary oncologist will consider all individual factors when determining whether lomustine is appropriate and how to optimize safety throughout treatment.

Lomustine capsules should be stored at room temperature between 68°F and 77°F (20°C and 25°C) in a tightly sealed container protected from light and moisture. The medication should be kept in its original pharmacy container whenever possible, as this packaging is designed to maintain drug stability and prevent light exposure. Storage locations should be secure, keeping the medication away from children, pets, and anyone not responsible for administration. Avoid storing lomustine near heat sources, in direct sunlight, or in humid areas such as bathrooms.

Compounded formulations of lomustine may have different storage requirements than commercial capsules. Compounding pharmacies provide specific storage instructions for their preparations, which may include refrigeration and limited stability periods. Pet owners should follow these instructions precisely and verify expiration or beyond-use dates before each use. Compounded medications that have exceeded their labeled stability period should not be administered and require proper disposal.

Safe handling of lomustine requires consistent protective measures due to the drug's classification as a hazardous substance. Always wear disposable gloves when handling capsules, and discard gloves after single use. Never touch capsules with bare hands. If a capsule is dropped, pick it up using gloves and inspect it for damage before returning it to the container or disposing of it if compromised. Do not crush, break, or open capsules, as this releases powdered drug that poses inhalation and contact hazards. Wash hands thoroughly after removing gloves and after any potential drug contact.

Proper disposal of unused or expired lomustine requires special consideration to protect the environment and prevent accidental exposure. Chemotherapy drugs should never be flushed down toilets or drains or placed in regular household garbage. Drug take-back programs offered by veterinary clinics, human pharmacies, or community organizations provide the safest disposal option for hazardous medications. The veterinary clinic dispensing the medication may accept unused portions for proper disposal. If no take-back option is available, contact local hazardous waste facilities for guidance on safe disposal methods in your area.

In the event of accidental spillage or capsule breakage, avoid direct contact with the material. Wear gloves and use damp paper towels to carefully collect spilled material, then clean the area with soap and water. Place all contaminated materials in a sealed plastic bag for disposal as hazardous waste. If skin contact occurs, wash the area immediately with soap and water for several minutes. If eye contact occurs, rinse thoroughly with water and seek medical attention. Report any significant exposures to a healthcare provider.

Lomustine can be administered to cats of all breeds without documented breed-specific sensitivities to the medication. Unlike dogs, where certain breeds carry genetic mutations affecting drug metabolism and toxicity, cats have not been shown to have breed-related differences in lomustine response. Veterinary oncologists apply standard dosing protocols across all feline breeds, making adjustments based on body size and individual patient factors rather than breed-specific concerns.

While breed-specific drug sensitivities are not established for lomustine in cats, certain breeds may be predisposed to developing the cancers for which lomustine is commonly prescribed. Siamese and other Oriental breeds have higher rates of certain types of lymphoma, particularly intestinal lymphoma, compared to other breeds. This predisposition means these breeds may more commonly receive lomustine as part of their cancer treatment. Understanding breed-related cancer risks helps veterinarians counsel owners about disease expectations rather than indicating any need for modified lomustine protocols.

Body size variations between cat breeds influence lomustine dosing calculations. Larger breeds such as Maine Coons and Norwegian Forest Cats may require larger total doses than smaller breeds like Singapuras or Devon Rex, though the dose per unit body surface area remains consistent. Accurate weight measurement is essential for proper dosing, as both underdosing (reducing effectiveness) and overdosing (increasing toxicity) carry significant consequences with chemotherapy medications. The veterinary oncologist calculates the appropriate dose based on current body weight using established body surface area formulas.

Age-related factors often take precedence over breed considerations in lomustine therapy decisions. Geriatric cats of all breeds require careful pre-treatment evaluation of organ function, as age-related changes in kidney and liver function are common regardless of breed. Older cats may be more susceptible to side effects and may require modified monitoring schedules or dose adjustments. Conversely, younger cats generally tolerate chemotherapy well but may face different tumor types and prognoses than geriatric patients. The veterinary oncology team considers age, overall health status, and tumor characteristics as primary factors in treatment planning, with breed serving as a secondary consideration primarily relevant to cancer predispositions rather than drug response.

Within the alkylating agent class, several alternatives to lomustine exist for feline cancer treatment, each with distinct characteristics influencing drug selection. Cyclophosphamide represents the most commonly used alkylating agent in veterinary oncology and forms the backbone of standard CHOP and COP protocols for lymphoma. Unlike lomustine, cyclophosphamide is available in both oral and injectable formulations and is typically administered more frequently (every 2-3 weeks versus every 4-6 weeks for lomustine). Chlorambucil offers another oral option particularly useful for low-grade lymphoma and chronic lymphocytic leukemia, with generally milder myelosuppression than lomustine.

Other alkylating agents used in feline oncology include melphalan and mechlorethamine. Melphalan finds primary use in treating multiple myeloma in cats and may appear in rescue protocols for lymphoma. Mechlorethamine has been used in combination with vincristine, melphalan, and prednisolone (MOMP protocol) as rescue therapy for resistant feline lymphoma. Each of these agents has different toxicity profiles, dosing schedules, and administration requirements that influence selection for individual patients.

Lomustine is often used in combination with other drug classes rather than as monotherapy. Multi-agent protocols may combine lomustine with methotrexate and cytarabine for rescue treatment of feline lymphoma, achieving response rates approaching 50% in some studies. Other combinations incorporate corticosteroids, vinca alkaloids, or antimetabolites depending on the specific protocol design. These combination approaches aim to attack cancer through multiple mechanisms while managing individual drug toxicities.

Supportive care medications play important roles alongside lomustine therapy. Anti-nausea drugs such as maropitant (Cerenia) help manage gastrointestinal side effects when they occur. Appetite stimulants may be prescribed for cats experiencing prolonged inappetence. Some oncologists recommend liver support supplements such as silymarin or SAMe, following precautions developed for dogs where hepatotoxicity is more clearly established. Pet owners should never add medications or supplements to their cat's regimen without veterinary approval, as interactions with chemotherapy could reduce effectiveness or increase toxicity. The veterinary oncology team will recommend appropriate supportive care tailored to each patient's needs throughout lomustine treatment.