Barbiturates reduce human cerebral glucose metabolism.

We studied the effect of barbiturates on local cerebral glucose metabolism by performing positron emission scans before and after withdrawal of phenobarbital or primidone. The postwithdrawal scan showed a significant increase (mean, 37%) in seven of eight cortical regions tested. Patients who had serial scans without a drug change showed a nonsignificant tendency for metabolic rates to go down on the second scan (mean decrease, 7%). Addition or deletion of a single drug other than barbiturate did not change metabolic rates on repeat scans. The depression in cerebral glucose metabolic rate due to phenobarbital, if confirmed, may have bearing on the adverse neuropsychological effects of the drug.