The therapeutic effects of systemic
dexamethasone,
methylprednisolone, predniso- lone and
prednisone are decreased by
phenobarbital. Other barbiturates (including primidone) probably interact similarly, although direct evidence is lacking. The
dexamethasone adrenal suppression test may be expected to be unreliable in those taking
phenobarbital.
Prednisone and
prednisolone appear to be less affected and therefore may be preferred. Monitor concurrent use to ensure corticosteroid
efficacy.