Listing of Drugs with Narrow Therapeutic Index

 

A drug with a narrow therapeutic index:

(1) has a narrow range of blood concentrations where it is therapeutic

(2) above the therapeutic range it quickly becomes toxic.

 

A drug with an NTI may change from beneficial to toxic if:

(1) the person is on a relatively high dose

(2) the person has any increase in dose

(3) the person has a drop in drug elimination sufficient to cause accumulation

(3a) worsening of organ function, especially renal failure

(3b) discontinuation of a therapy associated with increased elimination

 

Common drugs associated with a narrow therapeutic index:

(1) carbamazepine

(2) cyclosporine

(3) digoxin

(4) ethosuximide

(5) levothyroxine

(6) lithium

(7) phenytoin

(8) procainamide hydrochloride

(9) theophylline

(10) warfarin (coumadin)

 

On the other hand, a low dose, decrease in dose or increase in elimination may cause the patient to have subtherapeutic drug levels.