Page 354 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

332 PART III Therapeutic Modalities for the Cancer Patient

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to be effective against malignant melanoma, ascitic hepatoma, and These include, but are not limited to, St. John’s wort, kava-
Lewis lung carcinoma. Other research on mice has demonstrated kava, ginseng, garlic, milk thistle (silybin), evening primrose oil,
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green tea, Echinacea, vitamin E, beta-carotene, and quercetin
the ability of a mixture of botanical extracts made from fermented
VetBooks.ir soybeans, grape seed, green tea, and more to enhance the effective- supplements.
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ness of chemotherapy while limiting adverse effects.
Some plant mixtures both induce and inhibit drug-metabo-
Botanical products frequently encountered in veterinary inte- lizing enzymes because of the complexity of their biochemically
grative oncology include Asian mushrooms (immune-enhancing), active constituents. Many plant-based substances act as anti-
curcumin from the spice turmeric, Boswellia from the frankin- oxidants. The antioxidant activity of some phytotherapeutics such
cense tree (antitumor and antiinflammatory), and bloodroot as green tea is potent enough that clinicians should consider the
(escharotic), though the latter has fallen out of favor in recent risk of abrogating the benefits of chemotherapy if the two are
years because of its potential for causing injury and pain, as coadministered.
described in the text that follows. Veterinarians who decide to Another concern involves the potential for immune system
introduce botanical agents into a patient’s care should do so with stimulation by plant products that promote lymphocyte prolifera-
the same degree of caution and critical evaluation as one would tion. Although immune-enhancing herbs may help a patient fight
employ with any chemotherapy drug. The tendency to overlook some immunogenic cancers, adding these products (e.g., burdock
the potential for intrinsic toxicity or risk of herb–drug interactions root, astragalus, medicinal mushrooms, Echinacea) could prove
could lead to unforeseen problems such as a heightened bleeding counterproductive for conditions such as lymphoma.
risk or alterations in serum concentrations of prescribed drugs. Finally, several botanical ingredients can increase the risk of
Furthermore, little research exists on veterinary botanical prod- hemorrhage through inhibition of platelet activity and aggrega-
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ucts and their pharmacokinetics and pharmacodynamics remain tion. This could negatively affect patients with hemangiosar-
mostly a mystery, as do safe and effective dosing levels. coma, those undergoing biopsies or surgery, and individuals
receiving concurrent anticoagulant or antiplatelet medications.
Supplement Questions and Quality Control Issues Cancer patients may already have thrombocytopenia from che-
In contrast to the more tightly regulated pharmaceutical indus- motherapy or bone marrow infiltration (myelopthisis) that could
try, products comprising dietary supplements and herbal prod- compromise their capacity to clot.
ucts raise far-reaching concerns about manufacturing quality, A study of a standardized extract of Maitake mushroom in
purity, and reliability. Contamination with microbes, heavy met- dogs with lymphoma reported no objective value, although two
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als, and dirt from manufacturing, combined with undisclosed dogs did develop hyphema and one developed petechiae. These
adulteration with pharmaceuticals complicate the picture and agents can inhibit platelet function; whether the bleeding noted
can obscure the actual risk or benefit from the listed ingredi- in this study related to the Maitake mushroom or the lymphoma
ents. Chinese mixtures raise even more red flags, ranging from was unclear.
US Food and Drug Administration (FDA) import bans on the The “4 G’s” mnemonic (i.e., ginkgo, ginseng, ginger, and gar-
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importation of veterinary Chinese herbal products to the poten- lic) helps one remember which herbs most notably inhibit coagu-
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tial inclusion of endangered plant and animal species. Plant sub- lation. Many Chinese herbal formulations contain one or more
stitution, misidentification, and proprietary (secret) ingredients of these ingredients. That said, proprietary mixtures that fail to
leave additional gaps in health care providers’ trust in Chinese disclose the amounts of their ingredients to keep the mixture a
remedies. “trade secret” make it impossible for practitioners to ascertain the
level of risk that that supplement poses.
Risk of Treatment Interactions For more information on specific plant compounds and
Scrutinizing a patient’s entire integrative oncology treatment plan their interaction risk, the reader is referred to Memorial Sloan-
should help diminish the client’s reliance on redundant, superflu- Kettering Cancer Center’s website or their free app entitled “About
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ous, and/or counterproductive concurrent approaches. In particu- Herbs.”
lar, the risk/benefit ratio of adding or omitting a botanical product
should take into account the potential for herb-drug interactions. Additional Issues with Chinese Herbs
Pharmacologic interplay between medications and supplements Recommending traditional Chinese herbal medicine (TCHM)
could change circulating drug concentrations and render a che- based on rigorously derived discoveries in botanical research
motherapy, analgesic, or anesthetic compound ineffective or toxic. allows practitioners to discard untestable, abstract mecha-
Herbs that have anticancer effects but contain phytoestrogens nisms of action such as claiming that they “resolve stagnation,
such as Angelica sinensis may adversely affect patients with hor- invigorate Qi, and remove phlegm/damp accumulation.”
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mone-sensitive cancer. 42 Computerized databases may assist oncologists by enabling
Herb-drug interactions in oncology occur through a num- determination of relevant, potential interactions between anti-
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ber of pharmacodynamic and pharmacokinetic pathways, and cancer drugs and Chinese herbs. Even oncologists in China
much more remains to be learned about specific herbs, drugs, and are encouraging their colleagues to maintain a watchful eye for
clinical significance through research in veterinary target species. surprise sequelae. For example, one paper warned: “[P]rofes-
Often ignored among herbalists and oncologists alike, herb-drug sional complacency about TCM [Traditional Chinese Medi-
interactions pose a clinically relevant problem in oncology, due to cine] use is becoming less acceptable as the knowledge base of
the narrow therapeutic index of most cytotoxic drugs. In fact, TCM-induced toxicities and interactions expands. Being rich
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induction of drug-metabolizing enzymes and transporters may sources of bioactive xenobiotics, TCMs are frequent causes of
lower plasma levels of anticancer drugs and result in subsequent puzzling complications, including hepatotoxicity, nephrotoxic-
treatment failure. Inhibition of these detoxification pathways ity, and hematologic disorders.” 54
could also contribute to enhanced chemotherapy drug toxicity. Some TCHMs are chemosensitizing or radiosensitizing and
Several popular herbal products have been identified as likely to thus may cause conventional treatment to have more robust activ-
contribute to herb-drug interactions under certain conditions. ity, whereas others directly antagonize medication through one or
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