Can all drugs benefit from TDM? Not really. For TDM to be effective and useful, one or more of the following should apply:

• The effective concentration and toxic concentrations must be well-defined.
• The pharmacokinetics of the drug are known to be variable.
• The drug is given chronically.
• There is the potential for drug-to-drug interactions.
• The drug exhibits high protein binding.
• The toxicity will mimic the indication for the drug; toxicity may not be visible during an exam but will only be revealed with TDM.
• The patient is pregnant, very young, or elderly.
• Compliance or history with the drug is poor.