Mitoxantrone For Dogs

What Is Mitoxantrone for Dogs?

Mitoxantrone is a synthetic antineoplastic (anti-cancer drug) in the anthracenedione class of drugs. It is for intravenous (injection into the vein) use only. Veterinarians usually use mitoxantrone for dogs with lymphoma and bladder cancer.

It is similar in action to an older chemotherapeutic, doxorubicin (Adriamycin). Although mitoxantrone is considered less harmful to the heart than doxorubicin, it is still potentially harmful.

Brand Names

Novantrone^®

How Mitoxantrone for Dogs Works

Mitoxantrone inhibits an enzyme (topoisomerase) that plays a role in opening DNA for repair and alters bonding between DNA resulting in what is called intercalation. These two actions damage cancer cells and prevent them from replicating.

Common Uses of Mitoxantrone for Dogs

Mitoxantrone is often used for bladder tumors (transitional cell carcinomas) and lymphoma.

Bladder Cancer

Treatment of transitional cell carcinoma centers on chemotherapy with mitoxantrone, vinblastine, or carboplatin combined with piroxicam.³ In fact, a 2015 study found that at least 60% of dogs treated with piroxicam combined with either mitoxantrone or carboplatin achieved at least partial response to therapy.¹

Mitoxantrone use has also been studied both before and after radiation therapy for bladder cancer. In a retrospective study, overall survival was similar; however, it was noted that white blood cell toxicity was more severe in dogs treated with mitoxantrone.⁴ As such, radiation and mitoxantrone may not be the first-choice option for bladder cancer.

Lymphoma

There are many different protocols for the treatment of lymphoma. Mitoxantrone can be combined with cyclophosphamide, vincristine, and prednisone into a protocol commonly referred to as CMOP.

Two studies found that CMOP protocol provided a mean survival time that was not statistically different and caused fewer side effects than another commonly used protocol, CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone).^7,15 This means that the CMOP protocol may be another treatment choice for canine multicentric intermediate- to large-cell lymphoma.¹⁵ This may be particularly true for dogs who are at high risk of developing side effects from the doxorubicin in CHOP.

Mitoxantrone is often used as part of a rescue protocol for lymphoma. Rescue protocols are used when a dog has either come out of remission or is not responding to the first treatment chosen. For example, 14 of 15 dogs who were treated with mitoxantrone and dacarbazine after failing or coming out of remission after L-asparaginase (L)-CHOP responded to this protocol.⁵ Dogs were more likely to respond to the mitoxantrone and dacarbazine if they had achieved complete remission from the L-CHOP protocol the first time around. In this study, mitoxantrone was administered at 5 mg/m2 IV over 10 min followed by dacarbazine at 600 mg/m2 IV over 5 hr, every 3 wk.

Other Cancers

Although not the primary use, mitoxantrone has been used to treat other cancers.

For example, dogs diagnosed with malignant mesothelioma have been treated with 5-Fluorouracil (5-FU) only and carboplatin only or alternated with mitoxantrone.⁹ Mean survival time was eight times longer (234 days) for dogs receiving chemotherapy versus no treatment. This was a small study and additional work is needed to identify the optimal treatment approach for malignant mesothelioma in dogs.

In another small study, the medical records from 15 dogs with anal sac adenocarcinoma treated with radiotherapy and mitoxantrone after surgical removal of the primary tumor were reviewed retrospectively.¹⁴ The authors felt survival times (median 956 days) were supportive of this type of protocol.

In another study, ninety-five dogs with various cancers found to be refractory to one or more treatment modalities were evaluated.¹⁰ Fifty-seven (57) of the dogs had undergone surgery, 37 got chemotherapy other than mitoxantrone, four had radiation, and one was treated with whole-body hyperthermia.¹⁰ Partial or complete remission was obtained in approximately a quarter of all dogs treated with mitoxantrone.

Tumors in which there was a partial or complete remission included:¹⁰

• Lymphoma
• Squamous cell carcinoma
• Fibrosarcoma
• Thyroid carcinoma
• Transitional cell carcinoma
• Mammary adenocarcinoma
• Hepatocellular carcinoma
• Renal adenocarcinoma
• Rectal carcinoma
• Chondrosarcoma
• Oral malignant melanoma
• Cutaneous malignant melanoma
• Myxosarcoma
• Mesothelioma
• Hemangiopericytoma

When to Not Use Mitoxantrone for Dogs

Cardiac (heart) toxicity may be more common in patients with prior treatment with anthracyclines, which are agents with a similar action to anthracenedione. Heart toxicity may also be more common in dogs with prior mediastinal radiotherapy, or with pre-existing cardiovascular (heart and vessel) disease. A dog treated for lymphoma developed cardiac toxicity after being treated with three different anthracycline class drugs.¹³ The heart disease was attributed to the medications.

Patients with pre-existing bone marrow suppression generally should not be given mitoxantrone. However, sometimes the benefits are considered to outweigh the risks.

Studies haven’t been done yet to see if mitoxantrone is safe for dogs with impaired liver function, so we don’t know if it could be problematic for these dogs.⁸

How to Give Mitoxantrone

Mitoxantrone is always given as an intravenous injection in the veterinary office. A common dosage is 5 mg/m2 given once a week.

Mitoxantrone is often combined with cyclophosphamide, vincristine, and prednisone into a protocol often referred to as CMOP. Initial effects of therapy can be seen in the first few weeks.

Mitoxantrone can be combined with local radiation, but bloodwork needs to be monitored for low white blood cell counts before administration.

What If I Miss a Dose?

Scheduling should be handled by your veterinarian, so if you need to miss an appointment, speak with your veterinarian.

Storage and Handling

As a chemotherapy drug, mitoxantrone is only handled or given to pets by trained veterinary professionals. The solution is stored at room temperature and must be diluted prior to use.

Mitoxantrone Side Effects

The most common signs of toxicosis are:

• Vomiting
• Diarrhea
• Anorexia
• Sepsis secondary to bone marrow suppression

In one study, overdosing of mitoxantrone was identified immediately after drug administration with patients needing hospitalization for an average of 8 days. Adverse events included:¹¹

• neutropenia (94%)
• thrombocytopenia (88%)
• anemia (63%)
• diarrhea (63%)
• anorexia (56%)
• vomiting (38%)
• lethargy (31%)
• nausea (25%)

High grade neutropenia, a specific type of low white blood cells, was incredibly common in the study (94%). The drug filgrastim (brand name Neupogen), which stimulates the growth of white blood cells, was given, but it did not help the neutropenia.

In another study the severity of neutropenia was worse in smaller dogs.¹² Overall, dogs weighing less than or equal to 15 kg were more likely to develop the more severe grade 3 or 4 neutropenia. These dogs were often hospitalized.

As previously noted, heart problems are more likely to occur for dogs who have been treated with other anthracycline drugs, have had radiation to the chest, or who already have issues with heart function.

Dosage adjustments may need to be made for dogs with impaired liver function, as mitoxantrone and its metabolites are processed mostly by the liver.²

Noticeable but not significant: Mitoxantrone may impart a blue-green color to the urine and blue coloration of the sclera (white of the eye) for approximately 24 hours after administration.⁸