Switching to generic NTI drugs requires clear, specific communication to ensure patient safety. Learn what to say, what to monitor, and how to build trust when substituting critical medications like warfarin, levothyroxine, and phenytoin.
Prescriber Attitudes Toward NTI Drugs and Substitution: What Doctors Really Think
9 January, 2026
Prescribers remain cautious about substituting generic drugs for narrow therapeutic index (NTI) medications due to risks of therapeutic failure or toxicity. Despite FDA assurances, many doctors prefer brand-name NTI drugs for stability, especially with warfarin, levothyroxine, and tacrolimus. State laws, communication gaps, and real-world errors fuel ongoing debate.