Decades later, as the immune system wanes slightly with age normal part of the aging process or when the immune system is suppressed by medications such as cyclophosphamide the virus becomes active again. Adrenalectomy Since Cyclophosphamide has been reported to be more toxic in adrenalectomized dogs, adjustment of the doses of both replacement steroids and Cyclophosphamide may be necessary for the adrenalectomized patient. MESNA appears to neutralize the cyclophosphamide oral toxic metabolite of cyclophosphamide acrolein that is thought to be responsible for the bladder complications. The physician should be alert for possible combined drug actions, desirable or undesirable, involving cyclophosphamide even though cyclophosphamide has been used successfully concurrently with other drugs, including other cytotoxic drugs. It is eliminated primarily in the form of metabolites, but from to 25 of the dose is excreted in urine as unchanged drug.