Interaction of nitrofurantoin with diphenylhydantoin.

Left-sided motor seizures in a patient with an operated brain tumor were controlled with 300 mg/d DPH. The introduction of antimicrobial therapy with nitrofurantoin caused a fall of serum DPH levels and the recurrence of seizures, at the same time serum gammaGT values were increased. These changes were reversible after nitrofurantoin treatment was terminated. Both increased DPH metabolism or impaired absorption could be responsible for this effect. The concomittant increase of gammaGT could be interpreted as indirect evidence of hepatic enzyme induction with increased metabolism of DPH. It is important to note the possibility of such interaction so that better anticonvulsant control can be achieved.