Direct serum injection high-performance liquid chromatographic method for the simultaneous determination of phenobarbital, carbamazepine and phenytoin.

A method is described for the simultaneous measurement of serum levels of three antiepileptic drugs, phenobarbital, phenytoin and carbamazepine, by direct injection high-performance liquid chromatography on a 25-cm Pinkerton internal surface reversed-phase (ISRP) column. Several commonly available compounds were tested and found not to co-chromatograph with the three drugs of interest or the internal standard, 5-(p-methylphenyl)-5-phenylhydantoin. Results obtained on patients' samples with this method compared well with those from enzyme-multiplied immunoassay technique (EMIT).