[Monitoring serum levels of new antiepileptics]

Therapeutic monitoring of old antiepileptic drugs has been useful in improving their use in clinical practice. The new antiepileptic drugs have been developed with the idea that monitoring their serum levels was going to be unnecessary. We review the characteristics of the new antiepileptic drugs that can be relevant to their being monitored and their possible uses.

After discussion of the evolution of the therapeutic monitoring of antiepileptic drugs in general, we take a more detailed look at the requirements needed for it to be useful, such as the indications, the procedure and a correct interpretation of the results. We point out the reasons why monitoring the new antiepileptic drugs can be worthwhile and we examine the characteristics of felbamate, gabapentin, lamotrigine, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide which may be relevant in their monitoring. These include the type of kinetics, the factors that have an influence on the relationship between dosage and serum levels, the concentration/dose ratio, data on the relationship between serum levels and effects, the factors that can influence this relationship, as well as the characteristics of sampling.

The new antiepileptic drugs present a wide interindividual and intraindividual variability which leads us to believe that some of they may be suitable candidates for therapeutic monitoring, but at present no target ranges have been clearly defined for any of them. Therefore, routine monitoring cannot be recommended, but it may be useful to establish an individual reference level that allows control over compliance and dosage readjustment in the presence of factors that alter their pharmacokinetics. Specific prospective studies are needed to establish target ranges that allow to individualize dosage in the absence of clinical criteria and to resolve doubts about the efficacy and toxicity of these drugs. Quicker and simpler assays that make monitoring easier are also needed.