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Use of Anti-oxidants with Chemotherapy in Pets

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Last Modified: December 10, 2006

Dear OncoLink "Ask The Experts,"

Would you please comment on the administration of antioxidants (vitamins A, C, E) as supplementation to doxorubicin chemotherapy for canine mammary gland tumors, namely the ranges of allowed doses and routes of administration?

Karin Sorenmo, VMD, Director of the Medical Oncology division at The Ryan Veterinary Hospital of the University of Pennsylvania, responds:

The use of anti-oxidants concurrently with chemotherapy is quite controversial, and may in fact be contraindicated since some of them may actually interfere with the effectiveness of chemotherapy.

Many patients being treated for cancer use dietary supplements, particularly antioxidants, in the hopes of reducing the toxicity of chemotherapy and radiotherapy. Furthermore, some researchers have claimed that antioxidants also increase the effectiveness of cytotoxic therapy, and have explicitly recommended their use. However, mechanistic considerations suggest that antioxidants might actually reduce the effects of conventional cytotoxic therapies, which are thought to possibly fight cancer cells by oxidation. Preclinical data are currently inconclusive, and a limited number of clinical studies have not found any benefit. Clinicians should advise their patients against the use of antioxidant dietary supplements during chemotherapy or radiotherapy. Such caution should be seen as the standard approach for any unproven agent that may be harmful.

Based on this, I would not recommend any specific dose of antioxidants, since they are not proven to help, and may in fact decrease the efficacy of treatment.