Reducing the cost of phenytoin assays with in-house TDx reagents.

The Abbott TDx is frequently used for therapeutic drug monitoring of phenytoin concentrations, but reagent costs are high. In an attempt to reduce these costs, we investigated the preparation of in-house reagents. A commercial antiserum was available at reasonable cost and the fluorescent tracer was easily prepared. We describe the preparation of these reagents and their application to the TDx system. Substantially reduced costs were obtained using the in-house reagents.