Development and validation of a method for the determination of Topiramate by high-performance liquid chromatography coupled to a charged aerosol detector (HPLC-CAD)

Background
Topiramate (TPR) is a broad-spectrum antiepileptic indicated for the management of epilepsy in children and adults. In the absence of a formulation adapted to the paediatric population, our company would like to formulate an oral suspension of TPR at 6mg/mL. As this active substance lacks a chromophore group, the use of conventional UV-visible spectrophotometry detection methods is not feasible.

Objectives
To develop a stability-indicating HPLC-CAD assay for quality control of TPR oral suspensions. The method should enable efficient separation of TPR from its major impurities (A and E), as described in the European Pharmacopoeia, which are also its main degradation products.

Materials and method
The assay was developed in four stages: literature review; selection of stationary and mobile phases; adjustment of the equipment; evaluation of matrix effects. The chromatographic system consisted of a Thermofisher Scientific^® Vanquish HPLC chain coupled to a charged aerosol detector (CAD, VF-D20A). The TPR dosage method was validated in accordance with the ICH Q2 guidelines. Validation was conducted over three days, using three ranges of five points (0.05 – 0.15 mg/ml) and three control levels (0.08, 0.1, and 0.12 mg/ml) prepared separately by three different operators.

Results
Separation was carried out on an Agilent^® Zorbax Eclipse XDB-C18 column (4.6 x 250 mm, 5 µm) thermostated at 30°C and pressurized to 170 bar. The mobile phase was a 50/50 water/methanol mixture. Samples were eluted isocratically at a flow rate of 1ml/min and an injection volume of 20 µl. The detector evaporation temperature (CAD) was maintained at 35°C. TPR retention time was 8.3 min. The calibration curve showed linearity between 0.05 and 0.15 mg/ml, with a correlation coefficient R² = 0.99. The coefficients of variation for repeatability and intermediate precision were 0.73% and 4.0% respectively. The accuracy profile showed a mean recovery of 101.13% (CI95% = [100.15 ; 102.12 %]). No interference with impurities A and E, nor any matrix effect with the excipients, was observed.

Discussion/Conclusion
The validated HPLC-CAD TPR assay is accurate, faithful and repeatable. Its use will contribute to the study of the physicochemical stability of TPR oral suspensions formulated to determine their shelf life and storage conditions.

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