Cerebrospinal fluid and plasma glutamine elevation by anticonvulsant drugs: a potential diagnostic and therapeutic trap.

Administration of phenobarbitone or primidone can produce an elevation of glutamine and ornithine concentrations, together with a reduction of urea concentrations, in the fasting plasma and CSF of some infants, and in the CSF of some older epileptic patients. These two anticonvulsant drugs may interfere with the metabolic conversion of ammonia to urea, possibly by enzyme inhibition at the step of carbomoyl phosphate synthesis. The elevation of glutamine in plasma and CSF can mimic values found in some hyperammonemias. Recognition of this drug reaction can prevent erroneous diagnoses of genetically-determined urea cycle disorders and subsequent inappropriate therapy.