Narrow therapeutic index drugs

A narrow therapeutic index means the dose that works sits close to the dose that harms, so small changes in dose or blood level matter. The FDA has not published one official list.

A drug appears here only when its own label states a narrow therapeutic index or range, or directs dosing by measured blood levels. Each entry links the label section that says so.

Drugs whose label says so (9)

  • CarbamazepineAntiepileptics (anticonvulsants)

    The label gives a usual adult therapeutic level of 4 to 12 mcg/mL and directs measuring plasma levels to see whether they are in the therapeutic range when response is unsatisfactory or interacting drugs are added or stopped.

    Sources: [1][2][3][4]

  • DigoxinCardiac glycosides

    The label states that digoxin has a narrow therapeutic index. Serum levels below 0.5 ng/mL are linked to reduced efficacy and levels above 2 ng/mL to toxicity.

    Sources: [1][2]

  • GentamicinAminoglycosides

    The label directs measuring peak and trough serum gentamicin concentrations to keep doses effective and avoid toxic levels, adjusting to avoid prolonged peaks above 12 mcg/mL and troughs above 2 mcg/mL.

    Sources: [1][2]

  • LevothyroxineThyroid hormones

    The label states that levothyroxine has a narrow therapeutic index, so doses are titrated against TSH.

    Sources: [1]

  • LithiumMood stabilizers

    The label sets a target serum lithium range of 0.8 to 1.2 mEq/L and warns that toxic levels (1.5 mEq/L and up) sit close to it.

    Sources: [1][2][3]

  • PhenytoinAntiepileptics (anticonvulsants)

    The label sets a target total serum level of 10 to 20 mcg/mL and warns that levels sustained above that range cause toxicity.

    Sources: [1][2]

  • Valproic acidAntiepileptics (anticonvulsants)

    The label directs checking plasma levels against the accepted target range of 50 to 100 mcg/mL when response is unsatisfactory, and thrombocytopenia rises at higher levels.

    Sources: [1][2]

  • VancomycinGlycopeptide antibiotics

    The label directs measuring trough serum vancomycin levels to guide IV dosing, especially when kidney function is changing.

    Sources: [1][2]

  • WarfarinVitamin K antagonists

    The label states that warfarin has a narrow therapeutic range, so dosing is guided by INR.

    Sources: [1]

More study lists