Primidone pharmacokinetics

Pharmacokinetics Primidone is readily absorbed from the Gl tract. Phenobarbital appears in plasma after several days of continuous therapy. Therapeutic plasma concentrations are 5 to 12 mcg/mL for primidone and 15 to 40 mcg/mL for phenobarbital. PEMA and phenobarbital have longer half-lives (10 to 18 hours and... 

Sherwin, A. L., Ethosuximide Chnical use, m Antiepileptic Drugs, 4th ed.. Levy, R. H., Mattson, R. H., and Meldrum, B. S., Eds., Raven Press, New York, 1994. Battino, D., Estienne, M., and Avanzini, G., Chnical pharmacokinetics of antiepileptic drugs in paediatric patients. Part 1 Phenobarbital, primidone, valproic acid, ethosuximide and mesuximide, Clin. Pharmacokinet., 29 257-286, 1995. 

Nau, H. et al.. Placental transfer and pharmacokinetics of primidone and its metabolites, phenobarbital, PEMA and hydroxyphenobarbital in neonates and infants of epileptic mothers, Eur. J. Clin. Pharmacol, 18 18 2, 1980. 

Similarly, in another study, which compared the pharmacokinetics of a single dose of ethosuximide in 10 epileptic patients taking phenobarbital, phenytoin and/or carbamazepine with 12 healthy controls, the epileptic group had markedly shorter (about halved) ethosuximide half-lives. Conversely, another report stated that ethosuximide levels tended to rise [amount not stated] when methylphenobarbital was used (the opposite effect to that which would be expected), but did not appear to be affected by phenobarbital or primidone. Phenobarbital levels (from primidone) do not appear to be affected by ethosuximide. ... 

There is some evidence that the enzyme-inducing antiepileptics (carbamazepine, phenobarbital, phenytoin and primidone) may modestly reduce levetiracetam levels, but this is not thought to be clinically relevant. Levetiracetam does not usually alter the levels of these antiepileptics. However, some studies have found modestly raised phenytoin levels, and cases of possible carbamazepine toxicity have also been reported. There appears to be no pharmacokinetic interaction between levetiracetam and gabapentin, lamotrigine, or valproate. 

Topiramate appears not to alter the pharmacokinetics of phenobarbital or primidone. Phenobarbital reduces topiramate levels. 

Phenobarbital is a recognised potent liver eiKyme inducer that increases the metabolism of corticosteroids, thereby reducing their effects. Pharmacokinetic studies have shown that phenobarbital reduces the half-lives of these corticosteroids and increases their clearances by 40 to 209%. Primidone interacts in a similar way because it is metabolised in the body to phenobarbital. ... 

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