I respectfully disagree, and there is data to support this.
A number of drugs are excreted in significant concentrations in urine after intravenous administration. Cyclophosphamide is one of them. In fact, there is enough unchanged CY in the urine of a patient receiving high dose CY for transplant in 24 hours to treat a breast cancer patient. I think that's significant. And other drugs are excreted in even higher concentrations.
I suggest taking a look here for some eye-opening data on excretion.