Medicare Part D Will Not Longer Cover Macrobid 50 Mg/

Medicare Part D will not longer cover macrobid 50 mg/ twice daily, saying my husband is too old and has been receiving it too long. he has a fistual between bowel and bladder and must take this daily, throughout the year. What drug or combination of drugs can be substituted for it .( When he has gotten a UTI after taking 50 mg once /day he had to be hospitalized and given IV Levoquin )