How would you manage methotrexate therapy in an active rheumatoid arthritis patient undergoing treatment for latent TB with rifampin?  

There are no easy answers as both rifampin and INH combined with methotrexate are associated with enhanced hepatotoxicity. Monotherapy regimens, while generally well tolerated can cause hepatotoxicity leading to dose modification/interruption in about 5-10%.  All approved regimens can be tried...