Usefulness and limitations of monitoring serum levels of antiepileptic drugs

Abstract

Until the early 1990s six major compounds (carbamazepine, ethosuximide, phenobarbital, phenytoin, primidone, and valproic acid) were available for the treatment of epilepsy. However, these drugs have pharmacokinetic limitations, teratogenic potential, and a negative effect on cognitive functions that impairs the quality of patients' lives and limits the use of these drugs in some patients. In addition, 20–30% of patients are refractory to these drugs.The development of ten new antiepileptic drugs (vigabatrin, felbamate, gabapentin, lamotrigine, topiramate, tiagabine, oxcarbazepine, levetiracetam, zonisamide, and pregabalin) has expanded treatment options. The newer drugs may be better tolerated, have fewer drug interactions, and seem to affect cognitive functions to a lesser extent than old drugs. Guidelines on the use of new antiepileptic drugs have been developed in the USA and in the UK. Both guidelines offer a clear picture of the efficacy, safety, and tolerability of the new antiepileptic drugs and agree on their use as add-on treatment in patients who do not respond to conventional drugs. The guidelines differ in the type and strength of recommendations. Whereas the US guidelines recommend treatment in newly diagnosed epilepsy with a standard drug or a new drug depending on the individual patient's characteristics, the UK guidelines recommend that a new antiepileptic drug should be considered only if there is no benefit from an old antiepileptic drug, an old drug is contraindicated, there is a previous negative experience with the same drug, or the patient is a woman of childbearing potential.The limited amount of information on the new antiepileptic drugs may explain the discrepancies among the two guidelines and between these and other recommendations. Comparative, pragmatic, long-term and open trials should be done to show long-term efficacy and comparative features of the new antiepileptic drugs, and to better assess the effect on quality-of-life, cost-effectiveness, tolerability, and teratogenic potential. In addition, the conflicts should be resolved between the needs of the regulatory bodies and those of the treating physicians. Finally, there is a need for trial designs to be standardised.