Alternative Medicine Review 2000 (Apr); 5 (2): 152–163 ~ FULL TEXT
Davis W. Lamson, MS, ND and Matthew S. Brignall, ND
The previous lengthy review concerning the effects
of antioxidant compounds used concurrently with radiotherapy and chemotherapy
has been reduced to a reference guide. There are only three presently known
examples in which any agent classifiable as an antioxidant has been shown
to decrease effectiveness of radiation or chemotherapy in vivo. The vast
majority of both in vivo and in vitro studies have shown enhanced effectiveness
of standard cancer therapies or a neutral effect on drug action.
This guide is meant to be a companion to the previous review on effects
of antioxidant supplementation during cancer therapy.  Widespread use of antioxidant compounds makes this an area of increasing interest to oncologists as well as other physicians; hence, the attempt to reduce the findings of a lengthy report to a manageable guide.
Reducing complicated interactions to a single sentence can be an oversimplification.
In many instances the effect of an antioxidant compound with a certain
therapeutic agent may be specific to a particular tumor type, or may vary
with dosage of both antioxidant and chemotherapy. This guide is best used
as a means of quickly identifying which antioxidants are likely to be indicated
or contraindicated with a particular therapeutic agent. Please refer either
to the earlier review (Altern Med Rev 1999; 4 (5); 304-329) or the original
research reports for more information on these interactions.
Many of these interactions have been studied only in vitro. While an
in vitro result is often a predictor of in vivo response, this is not always
the case. The interaction between the bioflavonoid tangeretin and tamoxifen
is a good example of the risk in placing too much emphasis on in vitro
evidence. Tangeretin was found in vitro to act synergistically with tamoxifen;
but in vivo tangeretin completely reversed the inhibitory action of the
drug on experimental mammary tumors.  The
authors wish to emphasize that combinations not studied in vivo risk potential
adverse reactions and should be monitored closely or avoided altogether.
Similarly, it must be assumed that any antioxidant found to reduce in vivo
toxicity of cancer therapy on healthy tissue has the potential to decrease
effectiveness of the chemotherapy unless this was specifically studied.
The studies reporting reduced toxicity to healthy tissue of a therapeutic
agent with unknown effects on treatment outcomes are only reported if the
reduction was noted in human studies. The following tables summarize the
effect of various antioxidants when combined with specific chemotherapeutic
agents or radiation. Refer to Tables 1-7.
There are only three presently known examples in which an agent classifiable
as an antioxidant has been shown to decrease effectiveness of radiation
or chemotherapy in vivo. The vast majority of both in vivo and in vitro
studies have shown enhanced effectiveness of standard cancer therapies
or a neutral effect on drug action. The authors wish to thank Richard Russell
and the Smiling Dog Foundation for financial support of this project and
Bastyr University for its administration.