Lomustine (CCNU)

What is this medication for?

• CNS neoplasms (metabolites cross BBB), mast cell tumors, histiocytic sarcoma, lymphoma rescue

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• q3–6 week intervals mean one capsule every few weeks — the whole dose arrives at once; splitting or compounding for cats (10 mg) matters.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• stomach/intestinal (loss of appetite, vomiting, diarrhea), mouth sores (Common)

Worth a phone call to your veterinarian

• Delayed bone marrow suppression — nadirs 1–3 wk post-dose (low platelet counts prominent) (Most serious)
• Hepatotoxicity (dose-cumulative in dogs) (Documented — monitor LFTs)
• Rare: renal toxicity, pulmonary infiltrates/fibrosis, corneal de-epithelization, alopecia (Uncommon)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Anemia, marrow depression, pulmonary impairment, active infection, renal impairment, prior chemo/radiation — risk:benefit weighing

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Other myelosuppressives
  • Hepatotoxic drugs

Storage and handling

Chemo handling (gloves). Capsules; dosing intervals long — calendar discipline matters.

Good to know

• The delayed nadir is the trap: check blood at day 7 (trough) and again before the next dose (recovery) — a dog fine at discharge can be pancytopenic at day 14.
• CNS penetration via metabolites = why CCNU is a go-to for gliomas/meningiomas when chemotherapy is attempted.
• Mast cell tumors (post-toceranib era it remains a key oral option) and histiocytic sarcoma round out its niche.
• q3–6 week intervals mean one capsule every few weeks — the whole dose arrives at once; splitting or compounding for cats (10 mg) matters.