MY Husband Has One Kidney Only. Recently Creatin Was Higher

MY husband has one kidney only. Recently creatin was higher than 3 and his cancer doctor recommended he see his kidney specialist. He saw him and he said he did not see anything to be concerned about but to stop taking his benzaparil. He did not offer any alternative bp drug nor did he ask him to see his prescribing physician. I say this is wrong...do you agree. He has CML and is on Sprycel. Can this cause kidney concerns?