Here is the interaction caution about this drug as relayed in Health notes (6-10):
Cyclophosphamide requires activation by the liver through a process called oxidation. In theory, antioxidant nutrients (vitamin A, vitamin E, beta-carotene and others) might interfere with the activation of cyclophosphamide.
There is no published research linking antioxidant vitamins to reduced cyclophosphamide effectiveness in cancer treatment.
Don’t count on the new media or popular health publications to keep you fully informed about new medical findings. An article published in the December 25, 1996, issue of the Journal of the American Medical
Association (JAMA) showed that 200 mcg of supplemental selenium a day reduced overall cancer mortality by 50% in humans compared to a placebo group not receiving supplemental selenium. This 9-year study, published in the American Medical Association’s scientific journal (JAMA), demonstrated that a low-cost mineral supplement could cut the risk of dying from cancer in half.
(preliminary report by Subhuti Dharmananda, Ph.D., Director, Institute for Traditional Medicine, Portland, Oregon)
For more than 30 years now, Chinese herbs and materials derived from the herbs, such as long chain polysaccharides, have been used as adjunct therapies for cancer patients.
This modern application was first developed clinically in China and Japan during the 1970s and was relayed to the rest of the world in 1983 through an international conference in Beijing which was followed up by press reports in English and other languages (see: Physiological responses to immunologically active polysaccharides).
Even under the best conditions patients want to do everything possible to protect themselves from radiotherapy side effects. Many patients who undergo cancer treatments take vitamins and supplements. Until recently, oncologists seldom asked patients about this.