Performance characteristics of a new levetiracetam immunoassay and method comparison with a high-performance liquid...

Although levetiracetam is recognized for ease of dosing and being well tolerated, therapeutic drug monitoring is potentially useful in certain clinical situations. High-performance liquid chromatography has been commonly used for measuring levetiracetam. Recently, a homogeneous immunoassay for levetiracetam measurement in serum and plasma was introduced by ARK Diagnostics, Inc. The goal of this work was to validate this assay on a random access instrument.

This immunoassay was established on the Siemens ADVIA 1200 automated chemistry analyzer. The intraday precision was assessed by 10 replicates of two levels of quality control materials in a batch, whereas interday precision was estimated by assaying the same materials one set per day for 20 days. Linearity was evaluated by serially diluting the highest calibrator and a high patient specimen run in triplicate, whereas the lower limit of quantification was confirmed by 10 measurements of a low-level specimen diluted from a calibrator and another from a diluted patient specimen. This method was compared with a commercial high-performance liquid chromatography method (Chromsystems) using 63 specimens from patients who were on levetiracetam therapy.

The assay cycle was 10 minutes with a theoretical throughput of 800 per hour. The intra- (n = 10) and interday (n = 20) coefficients of variation were 8.1% or less for the two levels tested. The manufacturer-claimed analytical measurable range (2.0-100.0 μg/mL) was confirmed by serial dilution and lower limit of quantification experiments. Among the 63 patient samples studies, four showed levetiracetam levels below 2.0 μg/mL by both methods. Deming regression using the remaining 59 paired patient results by ARK immunoassay and the high-performance liquid chromatography method showed a correlation coefficient of 0.9962, a linear regression slope of 0.98, and an intercept of 0.61 with a mean bias of 0.04%.

The ARK immunoassay is suitable for clinical use of monitoring levetiracetam levels in serum/plasma on an automated chemistry analyzer (Siemens ADVIA 1200).