When is it not advisable to switch from patented/brand name drug to generic drugs?

Most patients on patented medicines can use the cheaper generic version when available.

However, when patients are on medicines with a narrow therapeutic or safety index that requires close monitoring and dose titration , (e.g. anti-rejection medicines such as Neoral, Prograf, Rapamune used after transplant or anticoagulants such as warfarin ) are usually kept on the same brand. Some other drugs with narrow therapeutic index include Digoxin and Valproic Acid