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[Rational combination therapy in epilepsy. II. Clinical and pharmacological aspects].

INTRODUCTION
From an analysis of the studies published to date, the criteria used to select the antiepileptic drugs that can be associated for the treatment of a particular situation or patient need to be optimised because combination therapy offers a low level of evidence. It is also acknowledged that it is advisable to begin treatment with monotherapy (although 30% of patients do not respond and in such cases combination therapy is usually employed), but the possibility of starting with bitherapy in epilepsies that are usually resistant to treatment has also been suggested.


DEVELOPMENT
This paper consists of three parts. This second part reviews the foundations underlying the rational association of antiepileptic drugs.


CONCLUSIONS
For the association of antiepileptic drugs to result in increased effectiveness without raising the level of toxicity, the theoretical bases of rational combination therapy take into account the mechanism of action, the spectrum, the safety, and the pharmacodynamic and pharmacokinetic interactions of each antiepileptic drug; the number of times the drug is taken is another factor to be taken into consideration. Although it is still early to associate two antiepileptic drugs on the basis of their mechanism of action, these theoretical foundations suggest a sodium channel inhibitor should be associated with a GABAergic agent or an antiepileptic with multiple mechanisms and that we should avoid the association between antiepileptic drugs with additional (sedative and neurological) toxicity or that are likely to interact. Evaluation of the effectiveness, safety, interactions and number of doses suggests the following order, from more to less suitable for combination therapy: levetiracetam/pregabalin > gabapentin > lamotrigine > oxcarbazepine/topiramate/zonisamide > tiagabine > valproic acid > carbamazepine > phenytoin > phenobarbital/primidone > benzodiazepines.