Tissue distribution of newer anticonvulsant drugs in postmortem cases

Levetiracetam, hydroxycarbazepine (the primary product of oxcarbazepine use), and topiramate were quantified using the acid/neutral drug screening procedure employed by this laboratory. Briefly, blood or tissue homogenate spiked with an internal standard (cyclopentobarbital) was buffered to pH 5 and applied to Chem Elut® columns. The columns were washed with methylene chloride, collected, and evaporated to dryness. The residue was reconstituted with 0.033 M trimethylanilinium hydroxide and injected into a gas chromatograph equipped with a DB-5 analytical column (25 m × 0.32-mm i.d.) and a nitrogen-phosphorus detector. A calibration curve using four calibrators ranging in concentration from 2 to 20 mg/L was used for quantification. Despite the limited number of cases for each drug, there were some trends suggested by the data. None of the drugs displayed significant differences in concentration between the heart blood and peripheral (subclavian) blood specimens. Only the hydroxycarbazepine quantifications in one case (case 5) showed significant differences between the two blood sites. This is consistent with other acid/neutral drugs such as acetaminophen and meprobamate. It also appears that the liver and kidney concentrations of the three drugs are on the same order of magnitude as the blood concentrations. Only the levetiracetam concentration in one case (case 3) reflected a liver or kidney concentration greater than 5 times the blood concentration.