Interactions between Antiepileptic Drugs
(AED)
-
May enhance toxicity without corresponding increase in antiepileptic
effects
-
Often complex and are highly variable and unpredictable
-
Plasma monitoring from blood tests is advisable with polytherapy
Carbamazepine
- often lowers plasma concentration of
clobazam, clonazepam, lamotrigine,
tiagabine, topiramate, valproate and phenytoin ( but may also raise
phenytoin concentration)
- sometime lowers
plasma concentration of ethosuximide and primidone ( but
tendency for corresponding increase in phenobarbital level due to increase
conversion of primidone to phenobarbital)
Phenytoin
- often lowers plasma concentration of
clonazepam, carbamazepine,
lamotrigine, tiagabine, topiramate and valproate.
- often raises plasma concentration of
phenobarbital
- sometime lowers
plasma concentration of ethosuximide and primidone ( but
tendency for corresponding increase in phenobarbital level due to increase
conversion of primidone to phenobarbital)
Valproate
- often raises the plasma concentration of an active metabolite of
carbamazepine, and of lamotrigine, primidone, phenobarbital and phenytoin
(which may also lower).
- sometime raises
plasma concentration of ethosuximide and primidone ( and
tendency for significant increase in phenobarbital level due to increase
conversion of primidone to phenobarbital)
Ethosuximide
- sometime raises the plasma concentration of
phenytoin
Lamotrigine
- sometimes raises the plasma concentration of an active metabolite of
carbamazepine
Phenobarbital or Primidone
- often lowers plasma concentration of
clonazepam, carbamazepine,
lamotrigine, tiagabine, valproate and phenytoin ( but may also raise
phenytoin concentration)
- sometimes lowers
plasma concentration of ethosuximide
Topiramate
- sometimes raises the plasma concentration of
phenytoin
Vigabatrin
- often lowers plasma concentration of
phenytoin
- sometime lowers plasma
concentration of primidone and phenobarbital.
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Reference : British
National Formulary 39 Edition Mar 2000