Summary
Forty-four dogs with histologically confirmed malignant tumors were used in a prospective study to determine the toxicity of the chemotherapeutic agent mitoxantrone, when administered at dosages higher than what has been previously reported for use in dogs. After each dose was administered, dogs were evaluated for signs of toxicosis for 3 weeks or until the dog developed progressive disease, died, or was euthanatized. Forty dogs had been refractory to 1 or more treatment modalities (surgery, n = 26; chemotherapy other than mitoxantrone, n = 17; radiation, n = 2) prior to entering this study. Ten dogs were given mitoxantrone at a dosage of 5.5 mg/m2 of body surface, IV, every 3 weeks (39 total doses); 11 were given mitoxantrone at a dosage of 6.0 mg/m2, IV, every 3 weeks (26 total doses); and 23 were given mitoxantrone at a dosage of 6.5 mg/m2, IV, every 3 weeks (70 total doses).
The most common signs of toxicosis were vomiting, anorexia, diarrhea, lethargy, and sepsis secondary to myelosuppression. Two dogs, both of which received the highest dosage, died of complications attributable to mitoxantrone administration. The prevalence of toxicoses was not associated with age, breed, sex, tumor type, number of doses, or dosage. Dogs did develop myelosuppression 7 days after they were given mitoxantrone. Median neutrophil count for dogs that received mitoxantrone at a dosage of 6.5 mg/m2 was 2,800 cells/μl (range, 300 to 4,600 cells/μl); median neutrophil count for dogs that received mitoxantrone at a dosage of 6.0 mg/m2 was 3,800 cells/μl (range, 600 to 10,400 cells/μl); and median neutrophil count for dogs that received mitoxantrone at a dosage of 5.5 mg/m2 was 4,500 cells/μl (range, 1,700 to 16,100 cells/μl).
