Comparison of topiramate concentrations in plasma and serum by fluorescence polarization immunoassay

Topiramate has been recently licensed as an antiepileptic drug. A fluoresce nce polarization immunoassay (FPIA), the Innofluor, has been developed to d etermine topiramate in heparinized plasma. Since therapeutic drug monitorin g laboratories may not have control over collection of the samples submitte d to them, it is important for analytical methods to be robust and able to cope with any specimen. The effect of different anticoagulants on the topir amate FPLA assay was investigated by collecting blood from 50 patients with epilepsy being maintained on a range of topiramate doses as part of their therapy. After venesection the blood was divided among lour tubes: plain, h eparinized, EDTA, and fluoride/oxalate. Erythrocytes were separated by cent rifugation and supernatant fluid frozen to await duplicate assay by FPIA. R esults were compared by means of Altman and Bland difference plots which in dicated that there was no significant difference between values obtained wi th heparinized plasma and the other fluids. It was concluded that the Innof luor assay is robust and gives similar results when blood samples are colle cted into any of the specified anticoagulants.