[Therapeutic drug monitoring of primidone and phenobarbital].

Primidone is a minor first-generation antiepileptic drug, little currently prescribed for this indication, but except marketing authorization, remains a first-line treatment of essential tremor. Although it is metabolized in phenyl-ethyl-malondamide and phenobarbital, active metabolites that contribute also to its action, primidone is not a prodrug and is active by itself. The rate of conversion of primidone to phenobarbital is highly variable according to the subject. Generally accepted therapeutic range for primidone is between 5 and 10 mg/L (23-46 mmol/L). The therapeutic drug monitoring (TDM) of primidone must be accompanied by the determination of phenobarbital concentrations. The level of proof of the interest of the TDM primidone was estimated to be "probably useless". Phenobarbital, a very ancient anticonvulsant, is much less used today, for the benefit of other more recent compounds. It remains prescribed in neonatology and is one of the compounds used in status epilepticus. It is a molecule with a long half-life, metabolized in p-hydroxy-phenobarbital. It is a potent inducer of CYP3A4. Several side effects, especially drowsiness, are concentration-dependent. Generally accepted therapeutic range for phenobarbital is between 10 and 40 mg/L (43 - 172 mmol/L), without considering the type of crise. The level of proof of the interest of TDM of phenobarbital was evaluated as "recommended".