Prescribers remain cautious about substituting generic drugs for narrow therapeutic index (NTI) medications like warfarin and levothyroxine due to risks of instability. While the FDA affirms generic safety, real-world data shows prescribers prioritize patient stability, leading to state-level restrictions and ongoing debate over substitution practices.
NTI drugs like levothyroxine and phenytoin require strict consistency to avoid life-threatening side effects. Yet many insurers still force patients through prior authorization to get the brand-name version they need - even when generics aren't safe substitutes.
Therapeutic Drug Monitoring (TDM) is critical for patients taking generic narrow therapeutic index (NTI) drugs, where small changes in blood levels can cause serious harm. Learn when and why TDM saves lives.