Rapid gas-chromatographic measurement of anticonvulsant drugs in serum.

We describe a rapid method for precisely measuring concentrations of anticonvulsant drugs in serum. The simple procedure, adaptable to the clinical laboratory, can be used for the routine simultaneous measurement in sera of phenobarbital, primidone, dephenylhydantoin, and (or) ethosuximide. The extraction procedure requires no solvent evaporation and gives a good yield for primidone and quantitative extraction for the other drugs. The relatively small amount of "early phenobarbital" formed during on-column methylation permits a precise analysis of phenobarbital based on a single peak. Results can be made available directly, without manual measurements or calculations.