Studies in man and animals clearly show that the barbiturates are potent liver
enzyme inducers. The most commonly used barbiturate is
phenobarbital, which is known to induce CYP3A4, amongst other isoenzymes. Most of the interaction information concerns
phenobarbital, but all barbiturates would be expected to share its inter- actions to a greater or lesser extent. Note that
primidone is metabolised to
phenobarbital, and so would therefore also be expected to share many of its interactions.