FPGEE 2026 Practice Exam for NABP – The Complete All-in-One Guide to Exam Success!

Narrow Therapeutic Index (NTI) drugs are medications that have a small margin between their therapeutic and toxic doses. This means that even a slight change in dosage or blood concentration can lead to ineffective treatment or toxicity.

Amoxicillin is an antibiotic that is generally considered to have a wide therapeutic index. This is because there is a significant difference between the effective dose and the dose that may lead to undesirable side effects or toxicity. The dosage of amoxicillin can be adjusted without significant risk of adverse effects as long as the prescribed regimen is followed appropriately.

In contrast, warfarin sodium, levothyroxine, and lithium are all classified as NTI drugs. Warfarin requires careful monitoring of INR levels to ensure the dose remains within the therapeutic range due to the risk of bleeding if levels are too high. Levothyroxine dosing must be carefully managed to avoid both hypothyroid and hyperthyroid states, and lithium requires regular serum monitoring to prevent toxicity.

Thus, amoxicillin is the only drug in the provided list that does not fit the criteria for a Narrow Therapeutic Index Drug.