Chemotherapy overdoses (ODs) are severe complications that can occur following the use of
antineoplastics. However, little is known about
chemotherapy ODs in veterinary medicine. The goals of this retrospective study were to report the occurrence, type, and cause of known
chemotherapy ODs in companion animal medicine. The American College of Veterinary Internal Medicine oncology and internal medicine listservs were solicited for
chemotherapy OD cases in dogs and cats. An OD was defined as administration of a
chemotherapy dose 10% higher than intended, or at a shorter interval than planned. Twelve non-
anthracycline ODs in 11 dogs, and 3 cat ODs, were collected. Overdoses in dogs included
carboplatin,
cyclophosphamide, L-
asparaginase,
lomustine,
mustargen,
vincristine, and
vinorelbine. The cat ODs included
doxorubicin and
vincristine. In dogs, the median OD was 2.1x (range: 1.2-10x) the intended dose. All dogs survived the OD and developed a variety of gastrointestinal and hematologic toxicities of varying grades. Both cats with a 2.4x
vincristine OD died despite supportive care. The cat who received a 2x OD of
doxorubicin survived the event, experiencing Veterinary Cooperative Oncology Group-common terminology criteria for adverse events (VCOG) grade I
thrombocytopenia and
anemia, and VCOG grade II
neutropenia.
Chemotherapy ODs appear to be rare in veterinary medicine and are typically 2-3xs the intended dose. Clinical effects include VCOG grade I and II gastrointestinal distress and VCOG grade III and IV hematologic effects. With appropriate supportive care, most patients will survive the event. Life-threatening events are more common in cats following
vincristine ODs.