STANDARDS OF LABORATORY PRACTICE - ANTIEPILEPTIC DRUG-MONITORING

Discussion and development of standards for appropriate monitoring led to the following key recommendations for ordering, sampling, and anal yzing antiepileptic drugs: Monitoring should usually be done on trough specimens after steady-state has been reached and always with an appr opriate medical indication; nonsteady-state concentrations may be indi cated in selected situations. Monitoring of free phenytoin and free va lproic acid is indicated in specific situations and should be done in serum. The metabolite of primidone, phenobarbital, should be measured concurrently with parent drug, but the active metabolite of carbamazep ine does not need to be monitored unless the patient is exhibiting an unusual toxic response that cannot be otherwise explained. Assays used for antiepileptic drug monitoring should display a long-term CV of <1 0% and preferably <5%. Subtherapeutic and supratherapeutic drug concen trations should be investigated on a regular basis as part of a qualit y assurance process.