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Phenobarbital is a barbiturate and primidone is a deoxybarbiturate effective in the treatment of generalized tonic-clonic and partial seizures (Table 13-1).1,2,3, and 4 Phenobarbital is available as a separate agent, but is also an active metabolite produced via hepatic metabolism during primidone treatment. Because of this, and because they share a similar antiseizure spectrum, these two drugs are considered together in this chapter. The probable mechanism of action for phenobarbital is elevation of seizure threshold by interacting with γ-aminobutyric acidA (GABAA) postsynaptic receptors which potentates synaptic inhibition.5,6 While the exact mechanism of action is not known for the antiepileptic effect of primidone, a portion of its antiseizure activity is due to its active metabolites phenobarbital and phenylethylmalonamide (PEMA).6,7
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