Mechlorethamine
Mechlorethamine hydrochloride
Also known as: Mustargen · Caryolysine · Onco-Cloramin · Nitrogen mustard · Mustine · HN2 · Chlormethine hydrochloride · Chlorethazine hydrochloride · NSC-762 · WR-147650
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This dose is based on body surface area (mg/m²). Convert body weight to body surface area before dosing.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Lymphoma rescue (MOPP protocol) | 3 mg/m2 IV | IV | given on days 0 and 7 (or days 0 and 14) of a 28 day protocol | 28 day cycles | 🌎 NA |
- Lymphoma rescue (MOPP protocol): Given as part of a protocol that includes vincristine (or vinblastine), procarbazine, and prednisone (or prednisolone).
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Lymphoma rescue (MOPP protocol) | 3 mg/m2 IV | IV | given on days 0 and 7 (or days 0 and 14) of a 28 day protocol | 28 day cycles | 🌎 NA |
- Lymphoma rescue (MOPP protocol): Given as part of a protocol that includes vincristine (or vinblastine), procarbazine, and prednisone (or prednisolone).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Mechlorethamine (also known as nitrogen mustard) is a highly potent, cell-cycle nonspecific antineoplastic agent. It is historically significant as the first nitrogen mustard alkylating agent used in chemotherapy.
In veterinary medicine, it is primarily utilized as an adjunctive treatment for lymphoreticular neoplasms, most notably as the "M" in the MOPP rescue protocol (Mechlorethamine, Oncovin [vincristine], Procarbazine, Prednisone) for relapsing canine and feline lymphoma.
Clinical Pearl: Mechlorethamine is a severe vesicant. Extreme care must be taken during intravenous administration to avoid extravasation, which can lead to devastating tissue necrosis and sloughing. Due to significant price increases and availability issues, some veterinary oncologists substitute dactinomycin or lomustine (CCNU) in rescue protocols.
It can also be administered intracavitarily to treat malignant pleural and peritoneal effusions, where it acts as a sclerosing agent to cause adherence of serosal surfaces.
Mechanism of action
Mechlorethamine is a bifunctional alkylating agent.
- Mechanism: It undergoes intramolecular cyclization to form a highly reactive aziridinium ion. This ion reacts with nucleophilic sites on DNA (primarily the N7 position of guanine).
- Pathway: Alkylation → Cross-linking of DNA strands (interstrand and intrastrand) → Inhibition of DNA replication and RNA transcription → Cell death (apoptosis).
- It is cell cycle-phase nonspecific, meaning it can kill cells in any phase of the cell cycle, though it is most toxic to rapidly dividing cells.
- When given intracavitarily, it induces a strong inflammatory response on serous membranes, leading to sclerosis and obliteration of the cavity space.
Safety & warnings
Contraindications
- Known infection
- Prior anaphylactic reaction to mechlorethamine
- Pregnancy (Category D teratogen)
- Anemia (relative)
- Bone marrow depression (relative)
- Tumor cell infiltration into bone marrow (relative)
- Patients who have received previous extensive chemotherapy or radiotherapy (relative)
Adverse effects
- Bone marrow depression (leukopenia, thrombocytopenia)
- Vomiting
- Nausea
- Ototoxicity (with high doses or regional perfusion)
- Alopecia
- Hyperuricemia
- Hepatotoxicity
- Peripheral neuropathy
- GI ulcers
- Severe tissue sloughing (if extravasated)
Precautions
Extravasation Risk: Mechlorethamine is a potent vesicant. Extravasation will cause severe tissue necrosis and sloughing. Ensure a perfectly placed, clean IV catheter before administration.
Hazardous Drug: This is a highly toxic antineoplastic agent. Strict hazardous drug handling protocols (gloves, gowns, biologic safety cabinet, closed-system transfer devices) must be utilized to protect veterinary personnel.
Teratogenicity: It is a known teratogen and can suppress gonadal function. Pregnant women should absolutely avoid handling this drug or the patient's waste.
Hyperuricemia: May raise serum uric acid levels; allopurinol may be required in susceptible patients.
Drug interactions
May increase the risk of severe infection.
Additive bone marrow depression; use with extreme caution.
Increased risk of vaccine-induced infection or decreased vaccine efficacy; use with caution or avoid.
Monitoring
- CBC with platelets (at least every 1-2 weeks until stable; then every 3 months)
- Liver function tests (initially before starting treatment and then every 3-4 months)
- Injection site for any signs of extravasation (redness, swelling, pain)
Pharmacokinetics
Absorption
Must be given IV for systemic use due to severe tissue irritation. Incompletely absorbed after intracavitary administration.
Distribution
Rapidly distributed but highly reactive.
Metabolism
Rapidly (within minutes) inactivated after injection.
Elimination
Rapidly degraded in the body.
Overdose
Because of the extreme toxic potential of this agent, overdoses must be strictly avoided. Dosages must be calculated carefully (usually based on Body Surface Area in m2). Overdose will likely result in profound, potentially fatal myelosuppression and severe gastrointestinal toxicity.
Available products
Formulations
- Powder for injection
Human-labeled
- Mechlorethamine Powder for Injection: 10 mg; Mustargen® (Lundbeck)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store the unconstituted powder at room temperature. Mechlorethamine is highly unstable in neutral or alkaline aqueous solutions and rapidly degrades. It must be administered immediately after preparation. Unused portions of reconstituted drug can be neutralized by adding equal volumes of 5% sodium thiosulfate and 5% sodium bicarbonate, allowed to stand for 45 minutes, and then discarded appropriately.
Client information
Important Safety Warning: Mechlorethamine is a potent chemotherapy drug. Pregnant women, nursing mothers, and children should not handle this medication or clean up the pet's waste (urine, feces, vomit) for at least 48-72 hours after treatment.
- Monitor the Injection Site: This drug can cause severe tissue damage if it leaks out of the vein. Check the IV site daily. If you notice any redness, swelling, pain, or licking at the site, contact your veterinarian immediately.
- Gastrointestinal Upset: Nausea and vomiting are common. Your veterinarian may prescribe anti-nausea medications to help keep your pet comfortable.
- Infection Risk: This drug lowers white blood cell counts, making your pet more susceptible to infections. Keep them away from sick animals and monitor for signs of illness, such as lethargy or fever.
- Nursing Pets: If a nursing mother is receiving this drug, puppies or kittens must be switched to a milk replacer.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.