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Procarbazine for Veterinary Use
by Barbara Forney, VMD
Procarbazine is a chemotherapeutic drug that is used as a part of the MOPP (mechlorethamine, vincristine, procarbazine and prednisone) protocol to treat relapsed lymphoma in dogs and cats. There also are studies that indicate that procarbazine may be useful as a sole, long-term treatment for granulomatous menigoencephalomyelitis in dogs.
Procarbazine is an atypical alkylating agent that inhibits RNA, DNA and protein synthesis. It is used in human medicine to treat brain tumors, such as oligodendroglioma and glioblastoma, and Hodgkin's Disease. Based on information extrapolated from human research, procarbazine is well absorbed orally and equilibrates rapidly between the plasma and cerebral spinal fluid (CSF). Procarbazine is metabolized by the liver and kidney and excreted in the urine. Urinary metabolites are cytotoxic.
Dogs and Cats
Procarbazine is used as a part of the MOPP protocol for relapsed lymphoma in dogs. In one study, which looked at the MOPP protocol in a group of dogs with advanced lymphoma, the median survival with treatment was 10 months. The only prognostic indicator for poor outcome in this group was inappetance at the time of diagnosis. The majority of dogs tolerated the MOPP protocol well.
The MOPP protocol is used both as first line chemotherapy and as rescue chemotherapy in cats with lymphoma. Cats that were eating well and not "sick" at the time of diagnosis tended to respond better to chemotherapy.
Procarbazine has been studied as a sole treatment for granulomatous menigoencephalomyelitis (GME) in dogs. GME is the second most common inflammatory disease of the central nervous system of dogs. It is more commonly seen in toy breeds. Left untreated, the survival time for dogs with GME is less than one month. GME was traditionally treated with prednisone, but recent studies have looked at treatment with procarbazine or cyclosporin. The procarbazine study showed an improved survival time of 14 months.
Procarbazine Side Effects
The most common side effects are gastrointestinal (GI), including anorexia, vomiting and diarrhea. In one study, GI toxicity occurred in 28% of treated animals. Bone marrow suppression, central nervous system (CNS) depression and peripheral neuropathy are less common but significant side-effects.
- Wear gloves when handling procarbazine and avoid contact with the animal's saliva and urine due to cytotoxic metabolites.
- Weekly monitoring of peripheral blood counts, hepatic and renal function should be performed for the first month of treatment and regularly thereafter.
- Procarbazine should be avoided or used with extreme caution in animals with pre-existing bone marrow suppression.
- Procarbazine should be used with caution in animals with decreased liver or kidney function.
- Procarbazine should not be used in pregnant or lactating animals. Procarbazine has been shown to adversely affect spermatogenesis. There are studies in the human literature discussing protocols to diminish testicular toxicity.
- Procarbazine should be used only with extreme caution with other CNS depressant drugs, including barbiturates, opiates, antihistamines and tranquilizers.
- Procarbazine should not be used with tricyclic antidepressant drugs or sympathomimetics. Ingestion of alcohol may cause severe nausea and vomiting.
- Animals receiving procarbazine should not be fed foods with high tyramine content (yogurt and some cheeses) due to adverse effects on blood pressure.
Overdose with procarbazine should be treated aggressively. If recognized promptly, gut
emptying protocols should be employed. Supportive care for GI upset, bone marrow suppression and CNS depression may be warranted.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at
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