Inotropics (drugs used to increase the pumping ability of the heart) and antiarrhythmics may need TDM. The cardiac glycoside inotropics digoxin and digitoxin have narrow therapeutic windows. Overdose can cause vomiting, diarrhea, confusion, visual disturbances, and cardiac arrhythmias. An interesting conundrum regarding these medications is that an overdose will produce the same symptoms that the drug is used to treat. For example, procainamide is used for arrhythmyia, but an overdose of procainamide can produce an arrhythmia. Thus, without TDM the physician will not know whether to give more drug or less drug, since both states can lead to the same presentation.
Examples of cardiac medications that are monitored by TDM include:
- Digoxin
- Digitoxin
- Procainamide
- N-acetylprocainamide (NAPA) -the metabolite of procainamide
- Quinidine
