Setting standards of practice in therapeutic drug monitoring and clinical toxicology: a North American view

Standards for therapeutic drug monitoring (TDM) must address the factors required for a valid TDM result. These are that the test be ordered with an appropriate indication, samples be obtained at the appropriate time, analysis be precise and accurate, and the result be interpreted and used correctly. General indications for ordering drug concentrations are to assess patient compliance, lack of response, adverse effects, initial or new baseline concentration after steady state has been achieved, and drug interactions. In establishing standards for clinical toxicology testing, the following points need to be considered: relatively few drugs will be involved in the majority of overdoses in a given location, the majority of drug overdoses and poisonings are treated symptomatically and supportively, and there are a relatively small number of drugs the testing of which may provide useful information in the emergency setting. An effective toxicology screen can be designed by first developing a list of candidate drugs that have antidotes, require specific treatment, are frequently encountered, or have a delayed onset of toxicity. Once such a list is in hand, it can be further evaluated to determine whether qualitative or quantitative testing is most appropriate and if rapid, convenient methods of analysis are available.