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 arryhthmias. A difficulty with these medications is that overdose produces the same symptoms that the drug is used to treat. For example, procainamide is used for arrythmyia, but an overdose of procainamide can produce an arrythmia. Thus, without TDM the physician will not know whether to give more drug or less, since both states can lead to the same presentation.
Examples of cardiac medications that are monitored by TDM include:
- N-acetylprocainamide (NAPA) -the metabolite of procainamide