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.
Unless criteria like these exist, it doesn't make much sense to perform TDM testing. Penicillin, for example is never measured in the serum. It has a wide therapeutic window, it is not given chronically, it has minimal toxicity, etc.