Cyclophosphamide (Cytoxan) Cyclophosphamide (CY) is administered intravenously at a dosage of 50 mg/kg on each of four successive days (use adjusted ideal body weight if patient's actual body weight is greater than 100% ideal body weight). The major dose limiting side effect at high doses is cardiac necrosis. Hemorrhagic cystitis can occur and is mediated by the acrolein metabolite. This can be prevented by co-administration of MESNA or bladder irrigation. Other notable side effects include nausea, vomiting, alopecia, myelosuppression and SIADH. Refer to institutional manuals for more information about administration, toxicity and complications.